path: root/doc/coreutils.info

This is coreutils.info, produced by makeinfo version 4.8 from
coreutils.texi.

INFO-DIR-SECTION Basics
START-INFO-DIR-ENTRY
* Coreutils: (coreutils).       Core GNU (file, text, shell) utilities.
* Common options: (coreutils)Common options.      Common options.
* File permissions: (coreutils)File permissions.  Access modes.
* Date input formats: (coreutils)Date input formats.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION Individual utilities
START-INFO-DIR-ENTRY
* base64: (coreutils)base64 invocation.         Base64 encode/decode data.
* basename: (coreutils)basename invocation.     Strip directory and suffix.
* cat: (coreutils)cat invocation.               Concatenate and write files.
* chgrp: (coreutils)chgrp invocation.           Change file groups.
* chmod: (coreutils)chmod invocation.           Change file permissions.
* chown: (coreutils)chown invocation.           Change file owners/groups.
* chroot: (coreutils)chroot invocation.         Specify the root directory.
* cksum: (coreutils)cksum invocation.           Print POSIX CRC checksum.
* comm: (coreutils)comm invocation.             Compare sorted files by line.
* cp: (coreutils)cp invocation.                 Copy files.
* csplit: (coreutils)csplit invocation.         Split by context.
* cut: (coreutils)cut invocation.               Print selected parts of lines.
* date: (coreutils)date invocation.             Print/set system date and time.
* dd: (coreutils)dd invocation.                 Copy and convert a file.
* df: (coreutils)df invocation.                 Report file system disk usage.
* dir: (coreutils)dir invocation.               List directories briefly.
* dircolors: (coreutils)dircolors invocation.   Color setup for ls.
* dirname: (coreutils)dirname invocation.       Strip non-directory suffix.
* du: (coreutils)du invocation.                 Report on disk usage.
* echo: (coreutils)echo invocation.             Print a line of text.
* env: (coreutils)env invocation.               Modify the environment.
* expand: (coreutils)expand invocation.         Convert tabs to spaces.
* expr: (coreutils)expr invocation.             Evaluate expressions.
* factor: (coreutils)factor invocation.         Print prime factors
* false: (coreutils)false invocation.           Do nothing, unsuccessfully.
* fmt: (coreutils)fmt invocation.               Reformat paragraph text.
* fold: (coreutils)fold invocation.             Wrap long input lines.
* groups: (coreutils)groups invocation.         Print group names a user is in.
* head: (coreutils)head invocation.             Output the first part of files.
* hostid: (coreutils)hostid invocation.         Print numeric host identifier.
* hostname: (coreutils)hostname invocation.     Print or set system name.
* id: (coreutils)id invocation.                 Print user identity.
* install: (coreutils)install invocation.       Copy and change attributes.
* join: (coreutils)join invocation.             Join lines on a common field.
* kill: (coreutils)kill invocation.             Send a signal to processes.
* link: (coreutils)link invocation.             Make hard links between files.
* ln: (coreutils)ln invocation.                 Make links between files.
* logname: (coreutils)logname invocation.       Print current login name.
* ls: (coreutils)ls invocation.                 List directory contents.
* md5sum: (coreutils)md5sum invocation.         Print or check MD5 digests.
* mkdir: (coreutils)mkdir invocation.           Create directories.
* mkfifo: (coreutils)mkfifo invocation.         Create FIFOs (named pipes).
* mknod: (coreutils)mknod invocation.           Create special files.
* mv: (coreutils)mv invocation.                 Rename files.
* nice: (coreutils)nice invocation.             Modify niceness.
* nl: (coreutils)nl invocation.                 Number lines and write files.
* nohup: (coreutils)nohup invocation.           Immunize to hangups.
* od: (coreutils)od invocation.                 Dump files in octal, etc.
* paste: (coreutils)paste invocation.           Merge lines of files.
* pathchk: (coreutils)pathchk invocation.       Check file name portability.
* pr: (coreutils)pr invocation.                 Paginate or columnate files.
* printenv: (coreutils)printenv invocation.     Print environment variables.
* printf: (coreutils)printf invocation.         Format and print data.
* ptx: (coreutils)ptx invocation.               Produce permuted indexes.
* pwd: (coreutils)pwd invocation.               Print working directory.
* readlink: (coreutils)readlink invocation.     Print referent of a symlink.
* rm: (coreutils)rm invocation.                 Remove files.
* rmdir: (coreutils)rmdir invocation.           Remove empty directories.
* seq: (coreutils)seq invocation.               Print numeric sequences
* sha1sum: (coreutils)sha1sum invocation.       Print or check SHA-1 digests.
* sha2: (coreutils)sha2 utilities.              Print or check SHA-2 digests.
* shred: (coreutils)shred invocation.           Remove files more securely.
* shuf: (coreutils)shuf invocation.             Shuffling text files.
* sleep: (coreutils)sleep invocation.           Delay for a specified time.
* sort: (coreutils)sort invocation.             Sort text files.
* split: (coreutils)split invocation.           Split into fixed-size pieces.
* stat: (coreutils)stat invocation.             Report file(system) status.
* stty: (coreutils)stty invocation.             Print/change terminal settings.
* su: (coreutils)su invocation.                 Modify user and group ID.
* sum: (coreutils)sum invocation.               Print traditional checksum.
* sync: (coreutils)sync invocation.             Synchronize memory and disk.
* tac: (coreutils)tac invocation.               Reverse files.
* tail: (coreutils)tail invocation.             Output the last part of files.
* tee: (coreutils)tee invocation.               Redirect to multiple files.
* test: (coreutils)test invocation.             File/string tests.
* touch: (coreutils)touch invocation.           Change file timestamps.
* tr: (coreutils)tr invocation.                 Translate characters.
* true: (coreutils)true invocation.             Do nothing, successfully.
* tsort: (coreutils)tsort invocation.           Topological sort.
* tty: (coreutils)tty invocation.               Print terminal name.
* uname: (coreutils)uname invocation.           Print system information.
* unexpand: (coreutils)unexpand invocation.     Convert spaces to tabs.
* uniq: (coreutils)uniq invocation.             Uniquify files.
* unlink: (coreutils)unlink invocation.         Removal via unlink(2).
* users: (coreutils)users invocation.           Print current user names.
* vdir: (coreutils)vdir invocation.             List directories verbosely.
* wc: (coreutils)wc invocation.                 Line, word, and byte counts.
* who: (coreutils)who invocation.               Print who is logged in.
* whoami: (coreutils)whoami invocation.         Print effective user ID.
* yes: (coreutils)yes invocation.               Print a string indefinitely.
END-INFO-DIR-ENTRY

   This manual documents version 6.9 of the GNU core utilities,
including the standard programs for text and file manipulation.

   Copyright (C) 1994, 1995, 1996, 2000, 2001, 2002, 2003, 2004, 2005,
2006 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included
     in the section entitled "GNU Free Documentation License".


File: coreutils.info,  Node: Top,  Next: Introduction,  Up: (dir)

GNU Coreutils
*************

This manual documents version 6.9 of the GNU core utilities, including
the standard programs for text and file manipulation.

   Copyright (C) 1994, 1995, 1996, 2000, 2001, 2002, 2003, 2004, 2005,
2006 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.2 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with no Front-Cover Texts,
     and with no Back-Cover Texts.  A copy of the license is included
     in the section entitled "GNU Free Documentation License".

* Menu:

* Introduction::                       Caveats, overview, and authors.
* Common options::                     Common options.
* Output of entire files::             cat tac nl od
* Formatting file contents::           fmt pr fold
* Output of parts of files::           head tail split csplit
* Summarizing files::                  wc sum cksum md5sum sha1sum sha2
* Operating on sorted files::          sort shuf uniq comm ptx tsort
* Operating on fields within a line::  cut paste join
* Operating on characters::            tr expand unexpand
* Directory listing::                  ls dir vdir dircolors
* Basic operations::                   cp dd install mv rm shred
* Special file types::                 ln mkdir rmdir mkfifo mknod
* Changing file attributes::           chgrp chmod chown touch
* Disk usage::                         df du stat sync
* Printing text::                      echo printf yes
* Conditions::                         false true test expr
* Redirection::                        tee
* File name manipulation::             dirname basename pathchk
* Working context::                    pwd stty printenv tty
* User information::                   id logname whoami groups users who
* System context::                     date uname hostname hostid
* Modified command invocation::        chroot env nice nohup su
* Process control::                    kill
* Delaying::                           sleep
* Numeric operations::                 factor seq
* File permissions::                   Access modes.
* Date input formats::                 Specifying date strings.
* Opening the software toolbox::       The software tools philosophy.
* Copying This Manual::                License for copying this manual.
* Index::                              General index.

 --- The Detailed Node Listing ---

Common Options

* Exit status::                 Indicating program success or failure.
* Backup options::              Backup options
* Block size::                  Block size
* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources::              Sources of random data
* Target directory::            Target directory
* Trailing slashes::            Trailing slashes
* Traversing symlinks::         Traversing symlinks to directories
* Treating / specially::        Treating / specially
* Standards conformance::       Standards conformance

Output of entire files

* cat invocation::              Concatenate and write files.
* tac invocation::              Concatenate and write files in reverse.
* nl invocation::               Number lines and write files.
* od invocation::               Write files in octal or other formats.
* base64 invocation::           Transform data into printable data.

Formatting file contents

* fmt invocation::              Reformat paragraph text.
* pr invocation::               Paginate or columnate files for printing.
* fold invocation::             Wrap input lines to fit in specified width.

Output of parts of files

* head invocation::             Output the first part of files.
* tail invocation::             Output the last part of files.
* split invocation::            Split a file into fixed-size pieces.
* csplit invocation::           Split a file into context-determined pieces.

Summarizing files

* wc invocation::               Print newline, word, and byte counts.
* sum invocation::              Print checksum and block counts.
* cksum invocation::            Print CRC checksum and byte counts.
* md5sum invocation::           Print or check MD5 digests.
* sha1sum invocation::          Print or check SHA-1 digests.
* sha2 utilities::              Print or check SHA-2 digests.

Operating on sorted files

* sort invocation::             Sort text files.
* shuf invocation::             Shuffle text files.
* uniq invocation::             Uniquify files.
* comm invocation::             Compare two sorted files line by line.
* ptx invocation::              Produce a permuted index of file contents.
* tsort invocation::            Topological sort.

`ptx': Produce permuted indexes

* General options in ptx::      Options which affect general program behavior.
* Charset selection in ptx::    Underlying character set considerations.
* Input processing in ptx::     Input fields, contexts, and keyword selection.
* Output formatting in ptx::    Types of output format, and sizing the fields.
* Compatibility in ptx::        The GNU extensions to `ptx'

Operating on fields within a line

* cut invocation::              Print selected parts of lines.
* paste invocation::            Merge lines of files.
* join invocation::             Join lines on a common field.

Operating on characters

* tr invocation::               Translate, squeeze, and/or delete characters.
* expand invocation::           Convert tabs to spaces.
* unexpand invocation::         Convert spaces to tabs.

`tr': Translate, squeeze, and/or delete characters

* Character sets::              Specifying sets of characters.
* Translating::                 Changing one set of characters to another.
* Squeezing::                   Squeezing repeats and deleting.

Directory listing

* ls invocation::               List directory contents
* dir invocation::              Briefly list directory contents
* vdir invocation::             Verbosely list directory contents
* dircolors invocation::        Color setup for `ls'

`ls':  List directory contents

* Which files are listed::      Which files are listed
* What information is listed::  What information is listed
* Sorting the output::          Sorting the output
* More details about version sort::  More details about version sort
* General output formatting::   General output formatting
* Formatting the file names::   Formatting the file names

Basic operations

* cp invocation::               Copy files and directories
* dd invocation::               Convert and copy a file
* install invocation::          Copy files and set attributes
* mv invocation::               Move (rename) files
* rm invocation::               Remove files or directories
* shred invocation::            Remove files more securely

Special file types

* link invocation::             Make a hard link via the link syscall
* ln invocation::               Make links between files
* mkdir invocation::            Make directories
* mkfifo invocation::           Make FIFOs (named pipes)
* mknod invocation::            Make block or character special files
* readlink invocation::         Print the referent of a symbolic link
* rmdir invocation::            Remove empty directories
* unlink invocation::           Remove files via unlink syscall

Changing file attributes

* chown invocation::            Change file owner and group
* chgrp invocation::            Change group ownership
* chmod invocation::            Change access permissions
* touch invocation::            Change file timestamps

Disk usage

* df invocation::               Report file system disk space usage
* du invocation::               Estimate file space usage
* stat invocation::             Report file or file system status
* sync invocation::             Synchronize data on disk with memory

Printing text

* echo invocation::             Print a line of text
* printf invocation::           Format and print data
* yes invocation::              Print a string until interrupted

Conditions

* false invocation::              Do nothing, unsuccessfully
* true invocation::               Do nothing, successfully
* test invocation::               Check file types and compare values
* expr invocation::               Evaluate expressions

`test': Check file types and compare values

* File type tests::               File type tests
* Access permission tests::       Access permission tests
* File characteristic tests::     File characteristic tests
* String tests::                  String tests
* Numeric tests::                 Numeric tests

`expr': Evaluate expression

* String expressions::         + : match substr index length
* Numeric expressions::        + - * / %
* Relations for expr::         | & < <= = == != >= >
* Examples of expr::           Examples of using `expr'

Redirection

* tee invocation::               Redirect output to multiple files

File name manipulation

* basename invocation::          Strip directory and suffix from a file name
* dirname invocation::           Strip non-directory suffix from a file name
* pathchk invocation::           Check file name portability

Working context

* pwd invocation::               Print working directory
* stty invocation::              Print or change terminal characteristics
* printenv invocation::          Print all or some environment variables
* tty invocation::               Print file name of terminal on standard input

`stty': Print or change terminal characteristics

* Control::                     Control settings
* Input::                       Input settings
* Output::                      Output settings
* Local::                       Local settings
* Combination::                 Combination settings
* Characters::                  Special characters
* Special::                     Special settings

User information

* id invocation::                Print user identity
* logname invocation::           Print current login name
* whoami invocation::            Print effective user ID
* groups invocation::            Print group names a user is in
* users invocation::             Print login names of users currently logged in
* who invocation::               Print who is currently logged in

System context

* date invocation::              Print or set system date and time
* uname invocation::             Print system information
* hostname invocation::          Print or set system name
* hostid invocation::            Print numeric host identifier.

`date': Print or set system date and time

* Time conversion specifiers::   %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::   %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers:: %[%nt]
* Padding and other flags::      Pad with zeros, spaces, etc.
* Setting the time::             Changing the system clock.
* Options for date::             Instead of the current time.
* Examples of date::             Examples.

Modified command invocation

* chroot invocation::            Run a command with a different root directory
* env invocation::               Run a command in a modified environment
* nice invocation::              Run a command with modified niceness
* nohup invocation::             Run a command immune to hangups
* su invocation::                Run a command with substitute user and group ID

Process control

* kill invocation::              Sending a signal to processes.

Delaying

* sleep invocation::             Delay for a specified time

Numeric operations

* factor invocation::            Print prime factors
* seq invocation::               Print numeric sequences

File permissions

* Mode Structure::               Structure of file mode bits.
* Symbolic Modes::               Mnemonic representation of file mode bits.
* Numeric Modes::                File mode bits as octal numbers.
* Directory Setuid and Setgid::  Set-user-ID and set-group-ID on directories.

Date input formats

* General date syntax::          Common rules.
* Calendar date items::          19 Dec 1994.
* Time of day items::            9:20pm.
* Time zone items::              EST, PDT, GMT.
* Day of week items::            Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings:: 19931219, 1440.
* Seconds since the Epoch::      @1078100502.
* Specifying time zone rules::   TZ="America/New_York", TZ="UTC0".
* Authors of get_date::          Bellovin, Eggert, Salz, Berets, et al.

Opening the software toolbox

* Toolbox introduction::         Toolbox introduction
* I/O redirection::              I/O redirection
* The who command::              The `who' command
* The cut command::              The `cut' command
* The sort command::             The `sort' command
* The uniq command::             The `uniq' command
* Putting the tools together::   Putting the tools together

Copying This Manual

* GNU Free Documentation License::  License for copying this manual.


File: coreutils.info,  Node: Introduction,  Next: Common options,  Prev: Top,  Up: Top

1 Introduction
**************

This manual is a work in progress: many sections make no attempt to
explain basic concepts in a way suitable for novices.  Thus, if you are
interested, please get involved in improving this manual.  The entire
GNU community will benefit.

   The GNU utilities documented here are mostly compatible with the
POSIX standard.  Please report bugs to <bug-coreutils@gnu.org>.
Remember to include the version number, machine architecture, input
files, and any other information needed to reproduce the bug: your
input, what you expected, what you got, and why it is wrong.  Diffs are
welcome, but please include a description of the problem as well, since
this is sometimes difficult to infer.  *Note Bugs: (gcc)Bugs.

   This manual was originally derived from the Unix man pages in the
distributions, which were written by David MacKenzie and updated by Jim
Meyering.  What you are reading now is the authoritative documentation
for these utilities; the man pages are no longer being maintained.  The
original `fmt' man page was written by Ross Paterson.  Franc,ois Pinard
did the initial conversion to Texinfo format.  Karl Berry did the
indexing, some reorganization, and editing of the results.  Brian
Youmans of the Free Software Foundation office staff combined the
manuals for textutils, fileutils, and sh-utils to produce the present
omnibus manual.  Richard Stallman contributed his usual invaluable
insights to the overall process.


File: coreutils.info,  Node: Common options,  Next: Output of entire files,  Prev: Introduction,  Up: Top

2 Common options
****************

Certain options are available in all of these programs.  Rather than
writing identical descriptions for each of the programs, they are
described here.  (In fact, every GNU program accepts (or should accept)
these options.)

   Normally options and operands can appear in any order, and programs
act as if all the options appear before any operands.  For example,
`sort -r passwd -t :' acts like `sort -r -t : passwd', since `:' is an
option-argument of `-t'.  However, if the `POSIXLY_CORRECT' environment
variable is set, options must appear before operands, unless otherwise
specified for a particular command.

   A few programs can usefully have trailing operands with leading `-'.
With such a program, options must precede operands even if
`POSIXLY_CORRECT' is not set, and this fact is noted in the program
description.  For example, the `env' command's options must appear
before its operands, since in some cases the operands specify a command
that itself contains options.

   Some of these programs recognize the `--help' and `--version'
options only when one of them is the sole command line argument.

`--help'
     Print a usage message listing all available options, then exit
     successfully.

`--version'
     Print the version number, then exit successfully.

`--'
     Delimit the option list.  Later arguments, if any, are treated as
     operands even if they begin with `-'.  For example, `sort -- -r'
     reads from the file named `-r'.


   A single `-' operand is not really an option, though it looks like
one.  It stands for standard input, or for standard output if that is
clear from the context.  For example, `sort -' reads from standard
input, and is equivalent to plain `sort', and `tee -' writes an extra
copy of its input to standard output.  Unless otherwise specified, `-'
can appear as any operand that requires a file name.

* Menu:

* Exit status::                 Indicating program success or failure.
* Backup options::              -b -S, in some programs.
* Block size::                  BLOCK_SIZE and --block-size, in some programs.
* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources::              --random-source, in some programs.
* Target directory::            Specifying a target directory, in some programs.
* Trailing slashes::            --strip-trailing-slashes, in some programs.
* Traversing symlinks::         -H, -L, or -P, in some programs.
* Treating / specially::        --preserve-root and --no-preserve-root.
* Special built-in utilities::  `break', `:', `eval', ...
* Standards conformance::       Conformance to the POSIX standard.


File: coreutils.info,  Node: Exit status,  Next: Backup options,  Up: Common options

2.1 Exit status
===============

Nearly every command invocation yields an integral "exit status" that
can be used to change how other commands work.  For the vast majority
of commands, an exit status of zero indicates success.  Failure is
indicated by a nonzero value--typically `1', though it may differ on
unusual platforms as POSIX requires only that it be nonzero.

   However, some of the programs documented here do produce other exit
status values and a few associate different meanings with the values
`0' and `1'.  Here are some of the exceptions: `chroot', `env', `expr',
`nice', `nohup', `printenv', `sort', `su', `test', `tty'.


File: coreutils.info,  Node: Backup options,  Next: Block size,  Prev: Exit status,  Up: Common options

2.2 Backup options
==================

Some GNU programs (at least `cp', `install', `ln', and `mv') optionally
make backups of files before writing new versions.  These options
control the details of these backups.  The options are also briefly
mentioned in the descriptions of the particular programs.

`-b'
`--backup[=METHOD]'
     Make a backup of each file that would otherwise be overwritten or
     removed.  Without this option, the original versions are destroyed.
     Use METHOD to determine the type of backups to make.  When this
     option is used but METHOD is not specified, then the value of the
     `VERSION_CONTROL' environment variable is used.  And if
     `VERSION_CONTROL' is not set, the default backup type is
     `existing'.

     Note that the short form of this option, `-b' does not accept any
     argument.  Using `-b' is equivalent to using `--backup=existing'.

     This option corresponds to the Emacs variable `version-control';
     the values for METHOD are the same as those used in Emacs.  This
     option also accepts more descriptive names.  The valid METHODs are
     (unique abbreviations are accepted):

    `none'
    `off'
          Never make backups.

    `numbered'
    `t'
          Always make numbered backups.

    `existing'
    `nil'
          Make numbered backups of files that already have them, simple
          backups of the others.

    `simple'
    `never'
          Always make simple backups.  Please note `never' is not to be
          confused with `none'.


`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  If this option
     is not specified, the value of the `SIMPLE_BACKUP_SUFFIX'
     environment variable is used.  And if `SIMPLE_BACKUP_SUFFIX' is not
     set, the default is `~', just as in Emacs.



File: coreutils.info,  Node: Block size,  Next: Disambiguating names and IDs,  Prev: Backup options,  Up: Common options

2.3 Block size
==============

Some GNU programs (at least `df', `du', and `ls') display sizes in
"blocks".  You can adjust the block size and method of display to make
sizes easier to read.  The block size used for display is independent
of any file system block size.  Fractional block counts are rounded up
to the nearest integer.

   The default block size is chosen by examining the following
environment variables in turn; the first one that is set determines the
block size.

`DF_BLOCK_SIZE'
     This specifies the default block size for the `df' command.
     Similarly, `DU_BLOCK_SIZE' specifies the default for `du' and
     `LS_BLOCK_SIZE' for `ls'.

`BLOCK_SIZE'
     This specifies the default block size for all three commands, if
     the above command-specific environment variables are not set.

`BLOCKSIZE'
     This specifies the default block size for all values that are
     normally printed as blocks, if neither `BLOCK_SIZE' nor the above
     command-specific environment variables are set.  Unlike the other
     environment variables, `BLOCKSIZE' does not affect values that are
     normally printed as byte counts, e.g., the file sizes contained in
     `ls -l' output.

`POSIXLY_CORRECT'
     If neither `COMMAND_BLOCK_SIZE', nor `BLOCK_SIZE', nor `BLOCKSIZE'
     is set, but this variable is set, the block size defaults to 512.


   If none of the above environment variables are set, the block size
currently defaults to 1024 bytes in most contexts, but this number may
change in the future.  For `ls' file sizes, the block size defaults to
1 byte.

   A block size specification can be a positive integer specifying the
number of bytes per block, or it can be `human-readable' or `si' to
select a human-readable format.  Integers may be followed by suffixes
that are upward compatible with the SI prefixes
(http://www.bipm.fr/enus/3_SI/si-prefixes.html) for decimal multiples
and with the IEC 60027-2 prefixes for binary multiples
(http://physics.nist.gov/cuu/Units/binary.html).

   With human-readable formats, output sizes are followed by a size
letter such as `M' for megabytes.  `BLOCK_SIZE=human-readable' uses
powers of 1024; `M' stands for 1,048,576 bytes.  `BLOCK_SIZE=si' is
similar, but uses powers of 1000 and appends `B'; `MB' stands for
1,000,000 bytes.

   A block size specification preceded by `'' causes output sizes to be
displayed with thousands separators.  The `LC_NUMERIC' locale specifies
the thousands separator and grouping.  For example, in an American
English locale, `--block-size="'1kB"' would cause a size of 1234000
bytes to be displayed as `1,234'.  In the default C locale, there is no
thousands separator so a leading `'' has no effect.

   An integer block size can be followed by a suffix to specify a
multiple of that size.  A bare size letter, or one followed by `iB',
specifies a multiple using powers of 1024.  A size letter followed by
`B' specifies powers of 1000 instead.  For example, `1M' and `1MiB' are
equivalent to `1048576', whereas `1MB' is equivalent to `1000000'.

   A plain suffix without a preceding integer acts as if `1' were
prepended, except that it causes a size indication to be appended to
the output.  For example, `--block-size="kB"' displays 3000 as `3kB'.

   The following suffixes are defined.  Large sizes like `1Y' may be
rejected by your computer due to limitations of its arithmetic.

`kB'
     kilobyte: 10^3 = 1000.

`k'
`K'
`KiB'
     kibibyte: 2^10 = 1024.  `K' is special: the SI prefix is `k' and
     the IEC 60027-2 prefix is `Ki', but tradition and POSIX use `k' to
     mean `KiB'.

`MB'
     megabyte: 10^6 = 1,000,000.

`M'
`MiB'
     mebibyte: 2^20 = 1,048,576.

`GB'
     gigabyte: 10^9 = 1,000,000,000.

`G'
`GiB'
     gibibyte: 2^30 = 1,073,741,824.

`TB'
     terabyte:  10^12 = 1,000,000,000,000.

`T'
`TiB'
     tebibyte: 2^40 = 1,099,511,627,776.

`PB'
     petabyte: 10^15 = 1,000,000,000,000,000.

`P'
`PiB'
     pebibyte: 2^50 = 1,125,899,906,842,624.

`EB'
     exabyte: 10^18 = 1,000,000,000,000,000,000.

`E'
`EiB'
     exbibyte: 2^60 = 1,152,921,504,606,846,976.

`ZB'
     zettabyte: 10^21 = 1,000,000,000,000,000,000,000

`Z'
`ZiB'
     2^70 = 1,180,591,620,717,411,303,424.  (`Zi' is a GNU extension to
     IEC 60027-2.)

`YB'
     yottabyte: 10^24 = 1,000,000,000,000,000,000,000,000.

`Y'
`YiB'
     2^80 = 1,208,925,819,614,629,174,706,176.  (`Yi' is a GNU
     extension to IEC 60027-2.)

   Block size defaults can be overridden by an explicit
`--block-size=SIZE' option.  The `-k' option is equivalent to
`--block-size=1K', which is the default unless the `POSIXLY_CORRECT'
environment variable is set.  The `-h' or `--human-readable' option is
equivalent to `--block-size=human-readable'.  The `--si' option is
equivalent to `--block-size=si'.


File: coreutils.info,  Node: Disambiguating names and IDs,  Next: Random sources,  Prev: Block size,  Up: Common options

2.4 chown and chgrp: Disambiguating user names and IDs
======================================================

Since the OWNER and GROUP arguments to `chown' and `chgrp' may be
specified as names or numeric IDs, there is an apparent ambiguity.
What if a user or group _name_ is a string of digits?  (1) Should the
command interpret it as a user name or as an ID?  POSIX requires that
`chown' and `chgrp' first attempt to resolve the specified string as a
name, and only once that fails, then try to interpret it as an ID.
This is troublesome when you want to specify a numeric ID, say 42, and
it must work even in a pathological situation where `42' is a user name
that maps to some other user ID, say 1000.  Simply invoking `chown 42
F', will set `F's owner ID to 1000--not what you intended.

   GNU `chown' and `chgrp' provide a way to work around this, that at
the same time may result in a significant performance improvement by
eliminating a database look-up.  Simply precede each numeric user ID
and/or group ID with a `+', in order to force its interpretation as an
integer:

     chown +42 F
     chgrp +$numeric_group_id another-file
     chown +0:+0 /

   GNU `chown' and `chgrp' skip the name look-up process for each
`+'-prefixed string, because a string containing `+' is never a valid
user or group name.  This syntax is accepted on most common Unix
systems, but not on Solaris 10.

   ---------- Footnotes ----------

   (1) Using a number as a user name is common in some environments.


File: coreutils.info,  Node: Random sources,  Next: Target directory,  Prev: Disambiguating names and IDs,  Up: Common options

2.5 Sources of random data
==========================

The `shuf', `shred', and `sort' commands sometimes need random data to
do their work.  For example, `sort -R' must choose a hash function at
random, and it needs random data to make this selection.

   Normally these commands use the device file `/dev/urandom' as the
source of random data.  Typically, this device gathers environmental
noise from device drivers and other sources into an entropy pool, and
uses the pool to generate random bits.  If the pool is short of data,
the device reuses the internal pool to produce more bits, using a
cryptographically secure pseudorandom number generator.

   `/dev/urandom' suffices for most practical uses, but applications
requiring high-value or long-term protection of private data may
require an alternate data source like `/dev/random' or `/dev/arandom'.
The set of available sources depends on your operating system.

   To use such a source, specify the `--random-source=FILE' option,
e.g., `shuf --random-source=/dev/random'.  The contents of FILE should
be as random as possible.  An error is reported if FILE does not
contain enough bytes to randomize the input adequately.

   To reproduce the results of an earlier invocation of a command, you
can save some random data into a file and then use that file as the
random source in earlier and later invocations of the command.

   Some old-fashioned or stripped-down operating systems lack support
for `/dev/urandom'.  On these systems commands like `shuf' by default
fall back on an internal pseudorandom generator initialized by a small
amount of entropy.


File: coreutils.info,  Node: Target directory,  Next: Trailing slashes,  Prev: Random sources,  Up: Common options

2.6 Target directory
====================

The `cp', `install', `ln', and `mv' commands normally treat the last
operand specially when it is a directory or a symbolic link to a
directory.  For example, `cp source dest' is equivalent to `cp source
dest/source' if `dest' is a directory.  Sometimes this behavior is not
exactly what is wanted, so these commands support the following options
to allow more fine-grained control:

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  This can help avoid race conditions
     in programs that operate in a shared area.  For example, when the
     command `mv /tmp/source /tmp/dest' succeeds, there is no guarantee
     that `/tmp/source' was renamed to `/tmp/dest': it could have been
     renamed to `/tmp/dest/source' instead, if some other process
     created `/tmp/dest' as a directory.  However, if `mv -T
     /tmp/source /tmp/dest' succeeds, there is no question that
     `/tmp/source' was renamed to `/tmp/dest'.

     In the opposite situation, where you want the last operand to be
     treated as a directory and want a diagnostic otherwise, you can use
     the `--target-directory' (`-t') option.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Use DIRECTORY as the directory component of each destination file
     name.

     The interface for most programs is that after processing options
     and a finite (possibly zero) number of fixed-position arguments,
     the remaining argument list is either expected to be empty, or is
     a list of items (usually files) that will all be handled
     identically.  The `xargs' program is designed to work well with
     this convention.

     The commands in the `mv'-family are unusual in that they take a
     variable number of arguments with a special case at the _end_
     (namely, the target directory).  This makes it nontrivial to
     perform some operations, e.g., "move all files from here to
     ../d/", because `mv * ../d/' might exhaust the argument space, and
     `ls | xargs ...' doesn't have a clean way to specify an extra
     final argument for each invocation of the subject command.  (It
     can be done by going through a shell command, but that requires
     more human labor and brain power than it should.)

     The `--target-directory' (`-t') option allows the `cp', `install',
     `ln', and `mv' programs to be used conveniently with `xargs'.  For
     example, you can move the files from the current directory to a
     sibling directory, `d' like this:

          ls | xargs mv -t ../d --

     However, this doesn't move files whose names begin with `.'.  If
     you use the GNU `find' program, you can move those files too, with
     this command:

          find . -mindepth 1 -maxdepth 1 \
            | xargs mv -t ../d

     But both of the above approaches fail if there are no files in the
     current directory, or if any file has a name containing a blank or
     some other special characters.  The following example removes
     those limitations and requires both GNU `find' and GNU `xargs':

          find . -mindepth 1 -maxdepth 1 -print0 \
            | xargs --null --no-run-if-empty \
                mv -t ../d


The `--target-directory' (`-t') and `--no-target-directory' (`-T')
options cannot be combined.


File: coreutils.info,  Node: Trailing slashes,  Next: Traversing symlinks,  Prev: Target directory,  Up: Common options

2.7 Trailing slashes
====================

Some GNU programs (at least `cp' and `mv') allow you to remove any
trailing slashes from each SOURCE argument before operating on it.  The
`--strip-trailing-slashes' option enables this behavior.

   This is useful when a SOURCE argument may have a trailing slash and
specify a symbolic link to a directory.  This scenario is in fact rather
common because some shells can automatically append a trailing slash
when performing file name completion on such symbolic links.  Without
this option, `mv', for example, (via the system's rename function) must
interpret a trailing slash as a request to dereference the symbolic link
and so must rename the indirectly referenced _directory_ and not the
symbolic link.  Although it may seem surprising that such behavior be
the default, it is required by POSIX and is consistent with other parts
of that standard.


File: coreutils.info,  Node: Traversing symlinks,  Next: Treating / specially,  Prev: Trailing slashes,  Up: Common options

2.8 Traversing symlinks
=======================

The following options modify how `chown' and `chgrp' traverse a
hierarchy when the `--recursive' (`-R') option is also specified.  If
more than one of the following options is specified, only the final one
takes effect.  These options specify whether processing a symbolic link
to a directory entails operating on just the symbolic link or on all
files in the hierarchy rooted at that directory.

   These options are independent of `--dereference' and
`--no-dereference' (`-h'), which control whether to modify a symlink or
its referent.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.



File: coreutils.info,  Node: Treating / specially,  Next: Special built-in utilities,  Prev: Traversing symlinks,  Up: Common options

2.9 Treating / specially
========================

Certain commands can operate destructively on entire hierarchies.  For
example, if a user with appropriate privileges mistakenly runs `rm -rf
/ tmp/junk', that may remove all files on the entire system.  Since
there are so few legitimate uses for such a command, GNU `rm' normally
declines to operate on any directory that resolves to `/'.  If you
really want to try to remove all the files on your system, you can use
the `--no-preserve-root' option, but the default behavior, specified by
the `--preserve-option', is safer for most purposes.

   The commands `chgrp', `chmod' and `chown' can also operate
destructively on entire hierarchies, so they too support these options.
Although, unlike `rm', they don't actually unlink files, these
commands are arguably more dangerous when operating recursively on `/',
since they often work much more quickly, and hence damage more files
before an alert user can interrupt them.  Tradition and POSIX require
these commands to operate recursively on `/', so they default to
`--no-preserve-root', but using the `--preserve-root' option makes them
safer for most purposes.  For convenience you can specify
`--preserve-root' in an alias or in a shell function.

   Note that the `--preserve-root' option also ensures that `chgrp' and
`chown' do not modify `/' even when dereferencing a symlink pointing to
`/'.


File: coreutils.info,  Node: Special built-in utilities,  Next: Standards conformance,  Prev: Treating / specially,  Up: Common options

2.10 Special built-in utilities
===============================

Some programs like `nice' can invoke other programs; for example, the
command `nice cat file' invokes the program `cat' by executing the
command `cat file'.  However, "special built-in utilities" like `exit'
cannot be invoked this way.  For example, the command `nice exit' does
not have a well-defined behavior: it may generate an error message
instead of exiting.

   Here is a list of the special built-in utilities that are
standardized by POSIX 1003.1-2004.

     . : break continue eval exec exit export readonly return set shift
     times trap unset

   For example, because `.', `:', and `exec' are special, the commands
`nice . foo.sh', `nice :', and `nice exec pwd' do not work as you might
expect.

   Many shells extend this list.  For example, Bash has several extra
special built-in utilities like `history', and `suspend', and with Bash
the command `nice suspend' generates an error message instead of
suspending.


File: coreutils.info,  Node: Standards conformance,  Prev: Special built-in utilities,  Up: Common options

2.11 Standards conformance
==========================

In a few cases, the GNU utilities' default behavior is incompatible
with the POSIX standard.  To suppress these incompatibilities, define
the `POSIXLY_CORRECT' environment variable.  Unless you are checking
for POSIX conformance, you probably do not need to define
`POSIXLY_CORRECT'.

   Newer versions of POSIX are occasionally incompatible with older
versions.  For example, older versions of POSIX required the command
`sort +1' to sort based on the second and succeeding fields in each
input line, but starting with POSIX 1003.1-2001 the same command is
required to sort the file named `+1', and you must instead use the
command `sort -k 2' to get the field-based sort.

   The GNU utilities normally conform to the version of POSIX that is
standard for your system.  To cause them to conform to a different
version of POSIX, define the `_POSIX2_VERSION' environment variable to
a value of the form YYYYMM specifying the year and month the standard
was adopted.  Two values are currently supported for `_POSIX2_VERSION':
`199209' stands for POSIX 1003.2-1992, and `200112' stands for POSIX
1003.1-2001.  For example, if you have a newer system but are running
software that assumes an older version of POSIX and uses `sort +1' or
`tail +10', you can work around any compatibility problems by setting
`_POSIX2_VERSION=199209' in your environment.


File: coreutils.info,  Node: Output of entire files,  Next: Formatting file contents,  Prev: Common options,  Up: Top

3 Output of entire files
************************

These commands read and write entire files, possibly transforming them
in some way.

* Menu:

* cat invocation::              Concatenate and write files.
* tac invocation::              Concatenate and write files in reverse.
* nl invocation::               Number lines and write files.
* od invocation::               Write files in octal or other formats.
* base64 invocation::           Transform data into printable data.


File: coreutils.info,  Node: cat invocation,  Next: tac invocation,  Up: Output of entire files

3.1 `cat': Concatenate and write files
======================================

`cat' copies each FILE (`-' means standard input), or standard input if
none are given, to standard output.  Synopsis:

     cat [OPTION] [FILE]...

   The program accepts the following options.  Also see *Note Common
options::.

`-A'
`--show-all'
     Equivalent to `-vET'.

`-b'
`--number-nonblank'
     Number all nonblank output lines, starting with 1.

`-e'
     Equivalent to `-vE'.

`-E'
`--show-ends'
     Display a `$' after the end of each line.

`-n'
`--number'
     Number all output lines, starting with 1.

`-s'
`--squeeze-blank'
     Replace multiple adjacent blank lines with a single blank line.

`-t'
     Equivalent to `-vT'.

`-T'
`--show-tabs'
     Display TAB characters as `^I'.

`-u'
     Ignored; for POSIX compatibility.

`-v'
`--show-nonprinting'
     Display control characters except for LFD and TAB using `^'
     notation and precede characters that have the high bit set with
     `M-'.


   On systems like MS-DOS that distinguish between text and binary
files, `cat' normally reads and writes in binary mode.  However, `cat'
reads in text mode if one of the options `-bensAE' is used or if `cat'
is reading from standard input and standard input is a terminal.
Similarly, `cat' writes in text mode if one of the options `-bensAE' is
used or if standard output is a terminal.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output f's contents, then standard input, then g's contents.
     cat f - g

     # Copy standard input to standard output.
     cat


File: coreutils.info,  Node: tac invocation,  Next: nl invocation,  Prev: cat invocation,  Up: Output of entire files

3.2 `tac': Concatenate and write files in reverse
=================================================

`tac' copies each FILE (`-' means standard input), or standard input if
none are given, to standard output, reversing the records (lines by
default) in each separately.  Synopsis:

     tac [OPTION]... [FILE]...

   "Records" are separated by instances of a string (newline by
default).  By default, this separator string is attached to the end of
the record that it follows in the file.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--before'
     The separator is attached to the beginning of the record that it
     precedes in the file.

`-r'
`--regex'
     Treat the separator string as a regular expression.  Users of `tac'
     on MS-DOS/MS-Windows should note that, since `tac' reads files in
     binary mode, each line of a text file might end with a CR/LF pair
     instead of the Unix-style LF.

`-s SEPARATOR'
`--separator=SEPARATOR'
     Use SEPARATOR as the record separator, instead of newline.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: nl invocation,  Next: od invocation,  Prev: tac invocation,  Up: Output of entire files

3.3 `nl': Number lines and write files
======================================

`nl' writes each FILE (`-' means standard input), or standard input if
none are given, to standard output, with line numbers added to some or
all of the lines.  Synopsis:

     nl [OPTION]... [FILE]...

   `nl' decomposes its input into (logical) pages; by default, the line
number is reset to 1 at the top of each logical page.  `nl' treats all
of the input files as a single document; it does not reset line numbers
or logical pages between files.

   A logical page consists of three sections: header, body, and footer.
Any of the sections can be empty.  Each can be numbered in a different
style from the others.

   The beginnings of the sections of logical pages are indicated in the
input file by a line containing exactly one of these delimiter strings:

`\:\:\:'
     start of header;

`\:\:'
     start of body;

`\:'
     start of footer.

   The two characters from which these strings are made can be changed
from `\' and `:' via options (see below), but the pattern and length of
each string cannot be changed.

   A section delimiter is replaced by an empty line on output.  Any text
that comes before the first section delimiter string in the input file
is considered to be part of a body section, so `nl' treats a file that
contains no section delimiters as a single body section.

   The program accepts the following options.  Also see *Note Common
options::.

`-b STYLE'
`--body-numbering=STYLE'
     Select the numbering style for lines in the body section of each
     logical page.  When a line is not numbered, the current line number
     is not incremented, but the line number separator character is
     still prepended to the line.  The styles are:

    `a'
          number all lines,

    `t'
          number only nonempty lines (default for body),

    `n'
          do not number lines (default for header and footer),

    `pBRE'
          number only lines that contain a match for the basic regular
          expression BRE.  *Note Regular Expressions: (grep)Regular
          Expressions.

`-d CD'
`--section-delimiter=CD'
     Set the section delimiter characters to CD; default is `\:'.  If
     only C is given, the second remains `:'.  (Remember to protect `\'
     or other metacharacters from shell expansion with quotes or extra
     backslashes.)

`-f STYLE'
`--footer-numbering=STYLE'
     Analogous to `--body-numbering'.

`-h STYLE'
`--header-numbering=STYLE'
     Analogous to `--body-numbering'.

`-i NUMBER'
`--page-increment=NUMBER'
     Increment line numbers by NUMBER (default 1).

`-l NUMBER'
`--join-blank-lines=NUMBER'
     Consider NUMBER (default 1) consecutive empty lines to be one
     logical line for numbering, and only number the last one.  Where
     fewer than NUMBER consecutive empty lines occur, do not number
     them.  An empty line is one that contains no characters, not even
     spaces or tabs.

`-n FORMAT'
`--number-format=FORMAT'
     Select the line numbering format (default is `rn'):

    `ln'
          left justified, no leading zeros;

    `rn'
          right justified, no leading zeros;

    `rz'
          right justified, leading zeros.

`-p'
`--no-renumber'
     Do not reset the line number at the start of a logical page.

`-s STRING'
`--number-separator=STRING'
     Separate the line number from the text line in the output with
     STRING (default is the TAB character).

`-v NUMBER'
`--starting-line-number=NUMBER'
     Set the initial line number on each logical page to NUMBER
     (default 1).

`-w NUMBER'
`--number-width=NUMBER'
     Use NUMBER characters for line numbers (default 6).


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: od invocation,  Next: base64 invocation,  Prev: nl invocation,  Up: Output of entire files

3.4 `od': Write files in octal or other formats
===============================================

`od' writes an unambiguous representation of each FILE (`-' means
standard input), or standard input if none are given.  Synopses:

     od [OPTION]... [FILE]...
     od [-abcdfilosx]... [FILE] [[+]OFFSET[.][b]]
     od [OPTION]... --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]

   Each line of output consists of the offset in the input, followed by
groups of data from the file.  By default, `od' prints the offset in
octal, and each group of file data is a C `short int''s worth of input
printed as a single octal number.

   If OFFSET is given, it specifies how many input bytes to skip before
formatting and writing.  By default, it is interpreted as an octal
number, but the optional trailing decimal point causes it to be
interpreted as decimal.  If no decimal is specified and the offset
begins with `0x' or `0X' it is interpreted as a hexadecimal number.  If
there is a trailing `b', the number of bytes skipped will be OFFSET
multiplied by 512.

   If a command is of both the first and second forms, the second form
is assumed if the last operand begins with `+' or (if there are two
operands) a digit.  For example, in `od foo 10' and `od +10' the `10'
is an offset, whereas in `od 10' the `10' is a file name.

   The program accepts the following options.  Also see *Note Common
options::.

`-A RADIX'
`--address-radix=RADIX'
     Select the base in which file offsets are printed.  RADIX can be
     one of the following:

    `d'
          decimal;

    `o'
          octal;

    `x'
          hexadecimal;

    `n'
          none (do not print offsets).

     The default is octal.

`-j BYTES'
`--skip-bytes=BYTES'
     Skip BYTES input bytes before formatting and writing.  If BYTES
     begins with `0x' or `0X', it is interpreted in hexadecimal;
     otherwise, if it begins with `0', in octal; otherwise, in decimal.
     Appending `b' multiplies BYTES by 512, `k' by 1024, and `m' by
     1048576.

`-N BYTES'
`--read-bytes=BYTES'
     Output at most BYTES bytes of the input.  Prefixes and suffixes on
     `bytes' are interpreted as for the `-j' option.

`-S N'
`--strings[=N]'
     Instead of the normal output, output only "string constants": at
     least N consecutive ASCII graphic characters, followed by a null
     (zero) byte.

     If N is omitted with `--strings', the default is 3.

`-t TYPE'
`--format=TYPE'
     Select the format in which to output the file data.  TYPE is a
     string of one or more of the below type indicator characters.  If
     you include more than one type indicator character in a single TYPE
     string, or use this option more than once, `od' writes one copy of
     each output line using each of the data types that you specified,
     in the order that you specified.

     Adding a trailing "z" to any type specification appends a display
     of the ASCII character representation of the printable characters
     to the output line generated by the type specification.

    `a'
          named character, ignoring high-order bit

    `c'
          ASCII character or backslash escape,

    `d'
          signed decimal

    `f'
          floating point

    `o'
          octal

    `u'
          unsigned decimal

    `x'
          hexadecimal

     The type `a' outputs things like `sp' for space, `nl' for newline,
     and `nul' for a null (zero) byte.  Only the least significant
     seven bits of each byte is used; the high-order bit is ignored.
     Type `c' outputs ` ', `\n', and `\0', respectively.

     Except for types `a' and `c', you can specify the number of bytes
     to use in interpreting each number in the given data type by
     following the type indicator character with a decimal integer.
     Alternately, you can specify the size of one of the C compiler's
     built-in data types by following the type indicator character with
     one of the following characters.  For integers (`d', `o', `u',
     `x'):

    `C'
          char

    `S'
          short

    `I'
          int

    `L'
          long

     For floating point (`f'):

    F
          float

    D
          double

    L
          long double

`-v'
`--output-duplicates'
     Output consecutive lines that are identical.  By default, when two
     or more consecutive output lines would be identical, `od' outputs
     only the first line, and puts just an asterisk on the following
     line to indicate the elision.

`-w[N]'
`--width[=N]'
     Dump `n' input bytes per output line.  This must be a multiple of
     the least common multiple of the sizes associated with the
     specified output types.

     If this option is not given at all, the default is 16.  If N is
     omitted, the default is 32.


   The next several options are shorthands for format specifications.
GNU `od' accepts any combination of shorthands and format specification
options.  These options accumulate.

`-a'
     Output as named characters.  Equivalent to `-t a'.

`-b'
     Output as octal bytes.  Equivalent to `-t o1'.

`-c'
     Output as ASCII characters or backslash escapes.  Equivalent to
     `-t c'.

`-d'
     Output as unsigned decimal two-byte units.  Equivalent to `-t u2'.

`-f'
     Output as floats.  Equivalent to `-t fF'.

`-i'
     Output as decimal ints.  Equivalent to `-t dI'.

`-l'
     Output as decimal long ints.  Equivalent to `-t dL'.

`-o'
     Output as octal two-byte units.  Equivalent to `-t o2'.

`-s'
     Output as decimal two-byte units.  Equivalent to `-t d2'.

`-x'
     Output as hexadecimal two-byte units.  Equivalent to `-t x2'.

`--traditional'
     Recognize the non-option label argument that traditional `od'
     accepted.  The following syntax:

          od --traditional [FILE] [[+]OFFSET[.][b] [[+]LABEL[.][b]]]

     can be used to specify at most one file and optional arguments
     specifying an offset and a pseudo-start address, LABEL.  The LABEL
     argument is interpreted just like OFFSET, but it specifies an
     initial pseudo-address.  The pseudo-addresses are displayed in
     parentheses following any normal address.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: base64 invocation,  Prev: od invocation,  Up: Output of entire files

3.5 `base64': Transform data into printable data.
=================================================

`base64' transforms data read from a file, or standard input, into (or
from) base64 encoded form.  The base64 encoded form uses printable
ASCII characters to represent binary data, see RFC 3548
(ftp://ftp.rfc-editor.org/in-notes/rfc3548.txt).  Synopses:

     base64 [OPTION]... [FILE]
     base64 --decode [OPTION]... [FILE]

   The base64 encoding expands data to roughly 133% of the original.

   The program accepts the following options.  Also see *Note Common
options::.

`-w COLS'
`--wrap=COLS'
     During encoding, wrap lines after COLS characters.  This must be a
     positive number.

     The default is to wrap after 76 characters.  Use the value 0 to
     disable line wrapping altogether.

`-d'
`--decode'
     Change the mode of operation, from the default of encoding data, to
     decoding data.  Input is expected to be base64 encoded data, and
     the output will be the original data.

`-i'
`--ignore-garbage'
     When decoding, newlines are always accepted.  During decoding,
     ignore unrecognized bytes, to permit distorted data to be decoded.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Formatting file contents,  Next: Output of parts of files,  Prev: Output of entire files,  Up: Top

4 Formatting file contents
**************************

These commands reformat the contents of files.

* Menu:

* fmt invocation::              Reformat paragraph text.
* pr invocation::               Paginate or columnate files for printing.
* fold invocation::             Wrap input lines to fit in specified width.


File: coreutils.info,  Node: fmt invocation,  Next: pr invocation,  Up: Formatting file contents

4.1 `fmt': Reformat paragraph text
==================================

`fmt' fills and joins lines to produce output lines of (at most) a
given number of characters (75 by default).  Synopsis:

     fmt [OPTION]... [FILE]...

   `fmt' reads from the specified FILE arguments (or standard input if
none are given), and writes to standard output.

   By default, blank lines, spaces between words, and indentation are
preserved in the output; successive input lines with different
indentation are not joined; tabs are expanded on input and introduced on
output.

   `fmt' prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence.  A "sentence break" is defined as either the end of
a paragraph or a word ending in any of `.?!', followed by two spaces or
end of line, ignoring any intervening parentheses or quotes.  Like TeX,
`fmt' reads entire "paragraphs" before choosing line breaks; the
algorithm is a variant of that given by Donald E. Knuth and Michael F.
Plass in "Breaking Paragraphs Into Lines", `Software--Practice &
Experience' 11, 11 (November 1981), 1119-1184.

   The program accepts the following options.  Also see *Note Common
options::.

`-c'
`--crown-margin'
     "Crown margin" mode: preserve the indentation of the first two
     lines within a paragraph, and align the left margin of each
     subsequent line with that of the second line.

`-t'
`--tagged-paragraph'
     "Tagged paragraph" mode: like crown margin mode, except that if
     indentation of the first line of a paragraph is the same as the
     indentation of the second, the first line is treated as a one-line
     paragraph.

`-s'
`--split-only'
     Split lines only.  Do not join short lines to form longer ones.
     This prevents sample lines of code, and other such "formatted"
     text from being unduly combined.

`-u'
`--uniform-spacing'
     Uniform spacing.  Reduce spacing between words to one space, and
     spacing between sentences to two spaces.

`-WIDTH'
`-w WIDTH'
`--width=WIDTH'
     Fill output lines up to WIDTH characters (default 75).  `fmt'
     initially tries to make lines about 7% shorter than this, to give
     it room to balance line lengths.

`-p PREFIX'
`--prefix=PREFIX'
     Only lines beginning with PREFIX (possibly preceded by whitespace)
     are subject to formatting.  The prefix and any preceding
     whitespace are stripped for the formatting and then re-attached to
     each formatted output line.  One use is to format certain kinds of
     program comments, while leaving the code unchanged.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: pr invocation,  Next: fold invocation,  Prev: fmt invocation,  Up: Formatting file contents

4.2 `pr': Paginate or columnate files for printing
==================================================

`pr' writes each FILE (`-' means standard input), or standard input if
none are given, to standard output, paginating and optionally
outputting in multicolumn format; optionally merges all FILEs, printing
all in parallel, one per column.  Synopsis:

     pr [OPTION]... [FILE]...

   By default, a 5-line header is printed at each page: two blank lines;
a line with the date, the file name, and the page count; and two more
blank lines.  A footer of five blank lines is also printed.  With the
`-F' option, a 3-line header is printed: the leading two blank lines are
omitted; no footer is used.  The default PAGE_LENGTH in both cases is 66
lines.  The default number of text lines changes from 56 (without `-F')
to 63 (with `-F').  The text line of the header takes the form `DATE
STRING PAGE', with spaces inserted around STRING so that the line takes
up the full PAGE_WIDTH.  Here, DATE is the date (see the `-D' or
`--date-format' option for details), STRING is the centered header
string, and PAGE identifies the page number.  The `LC_MESSAGES' locale
category affects the spelling of PAGE; in the default C locale, it is
`Page NUMBER' where NUMBER is the decimal page number.

   Form feeds in the input cause page breaks in the output.  Multiple
form feeds produce empty pages.

   Columns are of equal width, separated by an optional string (default
is `space').  For multicolumn output, lines will always be truncated to
PAGE_WIDTH (default 72), unless you use the `-J' option.  For single
column output no line truncation occurs by default.  Use `-W' option to
truncate lines in that case.

   The following changes were made in version 1.22i and apply to later
versions of `pr':  - Brian
   * Some small LETTER OPTIONS (`-s', `-w') have been redefined for
     better POSIX compliance.  The output of some further cases has
     been adapted to other Unix systems.  These changes are not
     compatible with earlier versions of the program.

   * Some NEW CAPITAL LETTER options (`-J', `-S', `-W') have been
     introduced to turn off unexpected interferences of small letter
     options.  The `-N' option and the second argument LAST_PAGE of
     `+FIRST_PAGE' offer more flexibility.  The detailed handling of
     form feeds set in the input files requires the `-T' option.

   * Capital letter options override small letter ones.

   * Some of the option-arguments (compare `-s', `-e', `-i', `-n')
     cannot be specified as separate arguments from the preceding
     option letter (already stated in the POSIX specification).

   The program accepts the following options.  Also see *Note Common
options::.

`+FIRST_PAGE[:LAST_PAGE]'
`--pages=FIRST_PAGE[:LAST_PAGE]'
     Begin printing with page FIRST_PAGE and stop with LAST_PAGE.
     Missing `:LAST_PAGE' implies end of file.  While estimating the
     number of skipped pages each form feed in the input file results
     in a new page.  Page counting with and without `+FIRST_PAGE' is
     identical.  By default, counting starts with the first page of
     input file (not first page printed).  Line numbering may be
     altered by `-N' option.

`-COLUMN'
`--columns=COLUMN'
     With each single FILE, produce COLUMN columns of output (default
     is 1) and print columns down, unless `-a' is used.  The column
     width is automatically decreased as COLUMN increases; unless you
     use the `-W/-w' option to increase PAGE_WIDTH as well.  This
     option might well cause some lines to be truncated.  The number of
     lines in the columns on each page are balanced.  The options `-e'
     and `-i' are on for multiple text-column output.  Together with
     `-J' option column alignment and line truncation is turned off.
     Lines of full length are joined in a free field format and `-S'
     option may set field separators.  `-COLUMN' may not be used with
     `-m' option.

`-a'
`--across'
     With each single FILE, print columns across rather than down.  The
     `-COLUMN' option must be given with COLUMN greater than one.  If a
     line is too long to fit in a column, it is truncated.

`-c'
`--show-control-chars'
     Print control characters using hat notation (e.g., `^G'); print
     other nonprinting characters in octal backslash notation.  By
     default, nonprinting characters are not changed.

`-d'
`--double-space'
     Double space the output.

`-D FORMAT'
`--date-format=FORMAT'
     Format header dates using FORMAT, using the same conventions as
     for the command `date +FORMAT'; *Note date invocation::.  Except
     for directives, which start with `%', characters in FORMAT are
     printed unchanged.  You can use this option to specify an
     arbitrary string in place of the header date, e.g.,
     `--date-format="Monday morning"'.

     Normally the date format defaults to `%Y-%m-%d %H:%M' (for
     example, `2001-12-04 23:59'); but if the `POSIXLY_CORRECT'
     environment variable is set and the `LC_TIME' locale category
     specifies the POSIX locale, the default is `%b %e %H:%M %Y' (for
     example, `Dec  4 23:59 2001'.

     Time stamps are listed according to the time zone rules specified
     by the `TZ' environment variable, or by the system default rules if
     `TZ' is not set.  *Note Specifying the Time Zone with `TZ':
     (libc)TZ Variable.

`-e[IN-TABCHAR[IN-TABWIDTH]]'
`--expand-tabs[=IN-TABCHAR[IN-TABWIDTH]]'
     Expand TABs to spaces on input.  Optional argument IN-TABCHAR is
     the input tab character (default is the TAB character).  Second
     optional argument IN-TABWIDTH is the input tab character's width
     (default is 8).

`-f'
`-F'
`--form-feed'
     Use a form feed instead of newlines to separate output pages.  The
     default page length of 66 lines is not altered.  But the number of
     lines of text per page changes from default 56 to 63 lines.

`-h HEADER'
`--header=HEADER'
     Replace the file name in the header with the centered string
     HEADER.  When using the shell, HEADER should be quoted and should
     be separated from `-h' by a space.

`-i[OUT-TABCHAR[OUT-TABWIDTH]]'
`--output-tabs[=OUT-TABCHAR[OUT-TABWIDTH]]'
     Replace spaces with TABs on output.  Optional argument OUT-TABCHAR
     is the output tab character (default is the TAB character).
     Second optional argument OUT-TABWIDTH is the output tab
     character's width (default is 8).

`-J'
`--join-lines'
     Merge lines of full length.  Used together with the column options
     `-COLUMN', `-a -COLUMN' or `-m'.  Turns off `-W/-w' line
     truncation; no column alignment used; may be used with
     `--sep-string[=STRING]'.  `-J' has been introduced (together with
     `-W' and `--sep-string') to disentangle the old (POSIX-compliant)
     options `-w' and `-s' along with the three column options.

`-l PAGE_LENGTH'
`--length=PAGE_LENGTH'
     Set the page length to PAGE_LENGTH (default 66) lines, including
     the lines of the header [and the footer].  If PAGE_LENGTH is less
     than or equal to 10 (or <= 3 with `-F'), the header and footer are
     omitted, and all form feeds set in input files are eliminated, as
     if the `-T' option had been given.

`-m'
`--merge'
     Merge and print all FILEs in parallel, one in each column.  If a
     line is too long to fit in a column, it is truncated, unless the
     `-J' option is used.  `--sep-string[=STRING]' may be used.  Empty
     pages in some FILEs (form feeds set) produce empty columns, still
     marked by STRING.  The result is a continuous line numbering and
     column marking throughout the whole merged file.  Completely empty
     merged pages show no separators or line numbers.  The default
     header becomes `DATE PAGE' with spaces inserted in the middle; this
     may be used with the `-h' or `--header' option to fill up the
     middle blank part.

`-n[NUMBER-SEPARATOR[DIGITS]]'
`--number-lines[=NUMBER-SEPARATOR[DIGITS]]'
     Provide DIGITS digit line numbering (default for DIGITS is 5).
     With multicolumn output the number occupies the first DIGITS
     column positions of each text column or only each line of `-m'
     output.  With single column output the number precedes each line
     just as `-m' does.  Default counting of the line numbers starts
     with the first line of the input file (not the first line printed,
     compare the `--page' option and `-N' option).  Optional argument
     NUMBER-SEPARATOR is the character appended to the line number to
     separate it from the text followed.  The default separator is the
     TAB character.  In a strict sense a TAB is always printed with
     single column output only.  The TAB-width varies with the
     TAB-position, e.g., with the left MARGIN specified by `-o' option.
     With multicolumn output priority is given to `equal width of
     output columns' (a POSIX specification).  The TAB-width is fixed
     to the value of the first column and does not change with
     different values of left MARGIN.  That means a fixed number of
     spaces is always printed in the place of the NUMBER-SEPARATOR TAB.
     The tabification depends upon the output position.

`-N LINE_NUMBER'
`--first-line-number=LINE_NUMBER'
     Start line counting with the number LINE_NUMBER at first line of
     first page printed (in most cases not the first line of the input
     file).

`-o MARGIN'
`--indent=MARGIN'
     Indent each line with a margin MARGIN spaces wide (default is
     zero).  The total page width is the size of the margin plus the
     PAGE_WIDTH set with the `-W/-w' option.  A limited overflow may
     occur with numbered single column output (compare `-n' option).

`-r'
`--no-file-warnings'
     Do not print a warning message when an argument FILE cannot be
     opened.  (The exit status will still be nonzero, however.)

`-s[CHAR]'
`--separator[=CHAR]'
     Separate columns by a single character CHAR.  The default for CHAR
     is the TAB character without `-w' and `no character' with `-w'.
     Without `-s' the default separator `space' is set.  `-s[char]'
     turns off line truncation of all three column options
     (`-COLUMN'|`-a -COLUMN'|`-m') unless `-w' is set.  This is a
     POSIX-compliant formulation.

`-SSTRING'
`--sep-string[=STRING]'
     Use STRING to separate output columns.  The `-S' option doesn't
     affect the `-W/-w' option, unlike the `-s' option which does.  It
     does not affect line truncation or column alignment.  Without
     `-S', and with `-J', `pr' uses the default output separator, TAB.
     Without `-S' or `-J', `pr' uses a `space' (same as `-S" "').
     `--sep-string' with no `=STRING' is equivalent to
     `--sep-string=""'.

`-t'
`--omit-header'
     Do not print the usual header [and footer] on each page, and do
     not fill out the bottom of pages (with blank lines or a form
     feed).  No page structure is produced, but form feeds set in the
     input files are retained.  The predefined pagination is not
     changed.  `-t' or `-T' may be useful together with other options;
     e.g.: `-t -e4', expand TAB characters in the input file to 4
     spaces but don't make any other changes.  Use of `-t' overrides
     `-h'.

`-T'
`--omit-pagination'
     Do not print header [and footer].  In addition eliminate all form
     feeds set in the input files.

`-v'
`--show-nonprinting'
     Print nonprinting characters in octal backslash notation.

`-w PAGE_WIDTH'
`--width=PAGE_WIDTH'
     Set page width to PAGE_WIDTH characters for multiple text-column
     output only (default for PAGE_WIDTH is 72).  `-s[CHAR]' turns off
     the default page width and any line truncation and column
     alignment.  Lines of full length are merged, regardless of the
     column options set.  No PAGE_WIDTH setting is possible with single
     column output.  A POSIX-compliant formulation.

`-W PAGE_WIDTH'
`--page_width=PAGE_WIDTH'
     Set the page width to PAGE_WIDTH characters.  That's valid with and
     without a column option.  Text lines are truncated, unless `-J' is
     used.  Together with one of the three column options (`-COLUMN',
     `-a -COLUMN' or `-m') column alignment is always used.  The
     separator options `-S' or `-s' don't affect the `-W' option.
     Default is 72 characters.  Without `-W PAGE_WIDTH' and without any
     of the column options NO line truncation is used (defined to keep
     downward compatibility and to meet most frequent tasks).  That's
     equivalent to `-W 72 -J'.  The header line is never truncated.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: fold invocation,  Prev: pr invocation,  Up: Formatting file contents

4.3 `fold': Wrap input lines to fit in specified width
======================================================

`fold' writes each FILE (`-' means standard input), or standard input
if none are given, to standard output, breaking long lines.  Synopsis:

     fold [OPTION]... [FILE]...

   By default, `fold' breaks lines wider than 80 columns.  The output
is split into as many lines as necessary.

   `fold' counts screen columns by default; thus, a tab may count more
than one column, backspace decreases the column count, and carriage
return sets the column to zero.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--bytes'
     Count bytes rather than columns, so that tabs, backspaces, and
     carriage returns are each counted as taking up one column, just
     like other characters.

`-s'
`--spaces'
     Break at word boundaries: the line is broken after the last blank
     before the maximum line length.  If the line contains no such
     blanks, the line is broken at the maximum line length as usual.

`-w WIDTH'
`--width=WIDTH'
     Use a maximum line length of WIDTH columns instead of 80.

     For compatibility `fold' supports an obsolete option syntax
     `-WIDTH'.  New scripts should use `-w WIDTH' instead.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Output of parts of files,  Next: Summarizing files,  Prev: Formatting file contents,  Up: Top

5 Output of parts of files
**************************

These commands output pieces of the input.

* Menu:

* head invocation::             Output the first part of files.
* tail invocation::             Output the last part of files.
* split invocation::            Split a file into fixed-size pieces.
* csplit invocation::           Split a file into context-determined pieces.


File: coreutils.info,  Node: head invocation,  Next: tail invocation,  Up: Output of parts of files

5.1 `head': Output the first part of files
==========================================

`head' prints the first part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopsis:

     head [OPTION]... [FILE]...

   If more than one FILE is specified, `head' prints a one-line header
consisting of:

     ==> FILE NAME <==

before the output for each FILE.

   The program accepts the following options.  Also see *Note Common
options::.

`-c N'
`--bytes=N'
     Print the first N bytes, instead of initial lines.  Appending `b'
     multiplies N by 512, `k' by 1024, and `m' by 1048576.  However, if
     N starts with a `-', print all but the last N bytes of each file.

`-n N'
`--lines=N'
     Output the first N lines.  However, if N starts with a `-', print
     all but the last N lines of each file.

`-q'
`--quiet'
`--silent'
     Never print file name headers.

`-v'
`--verbose'
     Always print file name headers.


   For compatibility `head' also supports an obsolete option syntax
`-COUNTOPTIONS', which is recognized only if it is specified first.
COUNT is a decimal number optionally followed by a size letter (`b',
`k', `m') as in `-c', or `l' to mean count by lines, or other option
letters (`cqv').  Scripts intended for standard hosts should use `-c
COUNT' or `-n COUNT' instead.  If your script must also run on hosts
that support only the obsolete syntax, it is usually simpler to avoid
`head', e.g., by using `sed 5q' instead of `head -5'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: tail invocation,  Next: split invocation,  Prev: head invocation,  Up: Output of parts of files

5.2 `tail': Output the last part of files
=========================================

`tail' prints the last part (10 lines by default) of each FILE; it
reads from standard input if no files are given or when given a FILE of
`-'.  Synopsis:

     tail [OPTION]... [FILE]...

   If more than one FILE is specified, `tail' prints a one-line header
consisting of:

     ==> FILE NAME <==

before the output for each FILE.

   GNU `tail' can output any amount of data (some other versions of
`tail' cannot).  It also has no `-r' option (print in reverse), since
reversing a file is really a different job from printing the end of a
file; BSD `tail' (which is the one with `-r') can only reverse files
that are at most as large as its buffer, which is typically 32 KiB.  A
more reliable and versatile way to reverse files is the GNU `tac'
command.

   If any option-argument is a number N starting with a `+', `tail'
begins printing with the Nth item from the start of each file, instead
of from the end.

   The program accepts the following options.  Also see *Note Common
options::.

`-c BYTES'
`--bytes=BYTES'
     Output the last BYTES bytes, instead of final lines.  Appending
     `b' multiplies BYTES by 512, `k' by 1024, and `m' by 1048576.

`-f'
`--follow[=HOW]'
     Loop forever trying to read more characters at the end of the file,
     presumably because the file is growing.  If more than one file is
     given, `tail' prints a header whenever it gets output from a
     different file, to indicate which file that output is from.

     There are two ways to specify how you'd like to track files with
     this option, but that difference is noticeable only when a
     followed file is removed or renamed.  If you'd like to continue to
     track the end of a growing file even after it has been unlinked,
     use `--follow=descriptor'.  This is the default behavior, but it
     is not useful if you're tracking a log file that may be rotated
     (removed or renamed, then reopened).  In that case, use
     `--follow=name' to track the named file by reopening it
     periodically to see if it has been removed and recreated by some
     other program.

     No matter which method you use, if the tracked file is determined
     to have shrunk, `tail' prints a message saying the file has been
     truncated and resumes tracking the end of the file from the
     newly-determined endpoint.

     When a file is removed, `tail''s behavior depends on whether it is
     following the name or the descriptor.  When following by name,
     tail can detect that a file has been removed and gives a message
     to that effect, and if `--retry' has been specified it will
     continue checking periodically to see if the file reappears.  When
     following a descriptor, tail does not detect that the file has
     been unlinked or renamed and issues no message;  even though the
     file may no longer be accessible via its original name, it may
     still be growing.

     The option values `descriptor' and `name' may be specified only
     with the long form of the option, not with `-f'.

     If `POSIXLY_CORRECT' is set, the `-f' option is ignored if no FILE
     operand is specified and standard input is a FIFO or a pipe.

`-F'
     This option is the same as `--follow=name --retry'.  That is, tail
     will attempt to reopen a file when it is removed.  Should this
     fail, tail will keep trying until it becomes accessible again.

`--retry'
     This option is useful mainly when following by name (i.e., with
     `--follow=name').  Without this option, when tail encounters a
     file that doesn't exist or is otherwise inaccessible, it reports
     that fact and never checks it again.

`--sleep-interval=NUMBER'
     Change the number of seconds to wait between iterations (the
     default is 1.0).  During one iteration, every specified file is
     checked to see if it has changed size.  Historical implementations
     of `tail' have required that NUMBER be an integer.  However, GNU
     `tail' accepts an arbitrary floating point number (using a period
     before any fractional digits).

`--pid=PID'
     When following by name or by descriptor, you may specify the
     process ID, PID, of the sole writer of all FILE arguments.  Then,
     shortly after that process terminates, tail will also terminate.
     This will work properly only if the writer and the tailing process
     are running on the same machine.  For example, to save the output
     of a build in a file and to watch the file grow, if you invoke
     `make' and `tail' like this then the tail process will stop when
     your build completes.  Without this option, you would have had to
     kill the `tail -f' process yourself.

          $ make >& makerr & tail --pid=$! -f makerr

     If you specify a PID that is not in use or that does not correspond
     to the process that is writing to the tailed files, then `tail'
     may terminate long before any FILEs stop growing or it may not
     terminate until long after the real writer has terminated.  Note
     that `--pid' cannot be supported on some systems; `tail' will
     print a warning if this is the case.

`--max-unchanged-stats=N'
     When tailing a file by name, if there have been N (default
     n=5) consecutive iterations for which the file has not changed,
     then `open'/`fstat' the file to determine if that file name is
     still associated with the same device/inode-number pair as before.
     When following a log file that is rotated, this is approximately
     the number of seconds between when tail prints the last
     pre-rotation lines and when it prints the lines that have
     accumulated in the new log file.  This option is meaningful only
     when following by name.

`-n N'
`--lines=N'
     Output the last N lines.

`-q'
`--quiet'
`--silent'
     Never print file name headers.

`-v'
`--verbose'
     Always print file name headers.


   For compatibility `tail' also supports an obsolete usage `tail
-[COUNT][bcl][f] [FILE]', which is recognized only if it does not
conflict with the usage described above.  This obsolete form uses
exactly one option and at most one file.  In the option, COUNT is an
optional decimal number optionally followed by a size letter (`b', `c',
`l') to mean count by 512-byte blocks, bytes, or lines, optionally
followed by `f' which has the same meaning as `-f'.

   On older systems, the leading `-' can be replaced by `+' in the
obsolete option syntax with the same meaning as in counts, and obsolete
usage overrides normal usage when the two conflict.  This obsolete
behavior can be enabled or disabled with the `_POSIX2_VERSION'
environment variable (*note Standards conformance::).

   Scripts intended for use on standard hosts should avoid obsolete
syntax and should use `-c COUNT[b]', `-n COUNT', and/or `-f' instead.
If your script must also run on hosts that support only the obsolete
syntax, you can often rewrite it to avoid problematic usages, e.g., by
using `sed -n '$p'' rather than `tail -1'.  If that's not possible, the
script can use a test like `if tail -c +1 </dev/null >/dev/null 2>&1;
then ...' to decide which syntax to use.

   Even if your script assumes the standard behavior, you should still
beware usages whose behaviors differ depending on the POSIX version.
For example, avoid `tail - main.c', since it might be interpreted as
either `tail main.c' or as `tail -- - main.c'; avoid `tail -c 4', since
it might mean either `tail -c4' or `tail -c 10 4'; and avoid `tail +4',
since it might mean either `tail ./+4' or `tail -n +4'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: split invocation,  Next: csplit invocation,  Prev: tail invocation,  Up: Output of parts of files

5.3 `split': Split a file into fixed-size pieces
================================================

`split' creates output files containing consecutive sections of INPUT
(standard input if none is given or INPUT is `-').  Synopsis:

     split [OPTION] [INPUT [PREFIX]]

   By default, `split' puts 1000 lines of INPUT (or whatever is left
over for the last section), into each output file.

   The output files' names consist of PREFIX (`x' by default) followed
by a group of characters (`aa', `ab', ... by default), such that
concatenating the output files in traditional sorted order by file name
produces the original input file.  If the output file names are
exhausted, `split' reports an error without deleting the output files
that it did create.

   The program accepts the following options.  Also see *Note Common
options::.

`-a LENGTH'
`--suffix-length=LENGTH'
     Use suffixes of length LENGTH.  The default LENGTH is 2.

`-l LINES'
`--lines=LINES'
     Put LINES lines of INPUT into each output file.

     For compatibility `split' also supports an obsolete option syntax
     `-LINES'.  New scripts should use `-l LINES' instead.

`-b BYTES'
`--bytes=BYTES'
     Put the first BYTES bytes of INPUT into each output file.
     Appending `b' multiplies BYTES by 512, `k' by 1024, and `m' by
     1048576.

`-C BYTES'
`--line-bytes=BYTES'
     Put into each output file as many complete lines of INPUT as
     possible without exceeding BYTES bytes.  For lines longer than
     BYTES bytes, put BYTES bytes into each output file until less than
     BYTES bytes of the line are left, then continue normally.  BYTES
     has the same format as for the `--bytes' option.

`-d'
`--numeric-suffixes'
     Use digits in suffixes rather than lower-case letters.

`--verbose'
     Write a diagnostic to standard error just before each output file
     is opened.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: csplit invocation,  Prev: split invocation,  Up: Output of parts of files

5.4 `csplit': Split a file into context-determined pieces
=========================================================

`csplit' creates zero or more output files containing sections of INPUT
(standard input if INPUT is `-').  Synopsis:

     csplit [OPTION]... INPUT PATTERN...

   The contents of the output files are determined by the PATTERN
arguments, as detailed below.  An error occurs if a PATTERN argument
refers to a nonexistent line of the input file (e.g., if no remaining
line matches a given regular expression).  After every PATTERN has been
matched, any remaining input is copied into one last output file.

   By default, `csplit' prints the number of bytes written to each
output file after it has been created.

   The types of pattern arguments are:

`N'
     Create an output file containing the input up to but not including
     line N (a positive integer).  If followed by a repeat count, also
     create an output file containing the next N lines of the input
     file once for each repeat.

`/REGEXP/[OFFSET]'
     Create an output file containing the current line up to (but not
     including) the next line of the input file that contains a match
     for REGEXP.  The optional OFFSET is an integer.  If it is given,
     the input up to (but not including) the matching line plus or
     minus OFFSET is put into the output file, and the line after that
     begins the next section of input.

`%REGEXP%[OFFSET]'
     Like the previous type, except that it does not create an output
     file, so that section of the input file is effectively ignored.

`{REPEAT-COUNT}'
     Repeat the previous pattern REPEAT-COUNT additional times.  The
     REPEAT-COUNT can either be a positive integer or an asterisk,
     meaning repeat as many times as necessary until the input is
     exhausted.


   The output files' names consist of a prefix (`xx' by default)
followed by a suffix.  By default, the suffix is an ascending sequence
of two-digit decimal numbers from `00' to `99'.  In any case,
concatenating the output files in sorted order by file name produces the
original input file.

   By default, if `csplit' encounters an error or receives a hangup,
interrupt, quit, or terminate signal, it removes any output files that
it has created so far before it exits.

   The program accepts the following options.  Also see *Note Common
options::.

`-f PREFIX'
`--prefix=PREFIX'
     Use PREFIX as the output file name prefix.

`-b SUFFIX'
`--suffix=SUFFIX'
     Use SUFFIX as the output file name suffix.  When this option is
     specified, the suffix string must include exactly one
     `printf(3)'-style conversion specification, possibly including
     format specification flags, a field width, a precision
     specifications, or all of these kinds of modifiers.  The format
     letter must convert a binary integer argument to readable form;
     thus, only `d', `i', `u', `o', `x', and `X' conversions are
     allowed.  The entire SUFFIX is given (with the current output file
     number) to `sprintf(3)' to form the file name suffixes for each of
     the individual output files in turn.  If this option is used, the
     `--digits' option is ignored.

`-n DIGITS'
`--digits=DIGITS'
     Use output file names containing numbers that are DIGITS digits
     long instead of the default 2.

`-k'
`--keep-files'
     Do not remove output files when errors are encountered.

`-z'
`--elide-empty-files'
     Suppress the generation of zero-length output files.  (In cases
     where the section delimiters of the input file are supposed to
     mark the first lines of each of the sections, the first output
     file will generally be a zero-length file unless you use this
     option.)  The output file sequence numbers always run
     consecutively starting from 0, even when this option is specified.

`-s'
`-q'
`--silent'
`--quiet'
     Do not print counts of output file sizes.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Summarizing files,  Next: Operating on sorted files,  Prev: Output of parts of files,  Up: Top

6 Summarizing files
*******************

These commands generate just a few numbers representing entire contents
of files.

* Menu:

* wc invocation::               Print newline, word, and byte counts.
* sum invocation::              Print checksum and block counts.
* cksum invocation::            Print CRC checksum and byte counts.
* md5sum invocation::           Print or check MD5 digests.
* sha1sum invocation::          Print or check SHA-1 digests.
* sha2 utilities::              Print or check SHA-2 digests.


File: coreutils.info,  Node: wc invocation,  Next: sum invocation,  Up: Summarizing files

6.1 `wc': Print newline, word, and byte counts
==============================================

`wc' counts the number of bytes, characters, whitespace-separated
words, and newlines in each given FILE, or standard input if none are
given or for a FILE of `-'.  Synopsis:

     wc [OPTION]... [FILE]...

   `wc' prints one line of counts for each file, and if the file was
given as an argument, it prints the file name following the counts.  If
more than one FILE is given, `wc' prints a final line containing the
cumulative counts, with the file name `total'.  The counts are printed
in this order: newlines, words, characters, bytes, maximum line length.
Each count is printed right-justified in a field with at least one
space between fields so that the numbers and file names normally line
up nicely in columns.  The width of the count fields varies depending
on the inputs, so you should not depend on a particular field width.
However, as a GNU extension, if only one count is printed, it is
guaranteed to be printed without leading spaces.

   By default, `wc' prints three counts: the newline, words, and byte
counts.  Options can specify that only certain counts be printed.
Options do not undo others previously given, so

     wc --bytes --words

prints both the byte counts and the word counts.

   With the `--max-line-length' option, `wc' prints the length of the
longest line per file, and if there is more than one file it prints the
maximum (not the sum) of those lengths.

   The program accepts the following options.  Also see *Note Common
options::.

`-c'
`--bytes'
     Print only the byte counts.

`-m'
`--chars'
     Print only the character counts.

`-w'
`--words'
     Print only the word counts.

`-l'
`--lines'
     Print only the newline counts.

`-L'
`--max-line-length'
     Print only the maximum line lengths.

`--files0-from=FILE'
     Rather than processing files named on the command line, process
     those named in file FILE; each name is terminated by a null byte.
     This is useful when the list of file names is so long that it may
     exceed a command line length limitation.  In such cases, running
     `wc' via `xargs' is undesirable because it splits the list into
     pieces and makes `wc' print a total for each sublist rather than
     for the entire list.  One way to produce a list of
     null-byte-terminated file names is with GNU `find', using its
     `-print0' predicate.  For example, to find the length of the
     longest line in any `.c' or `.h' file in the current hierarchy, do
     this:

          find . -name '*.[ch]' -print0 | wc -L --files0-from=- | tail -n1

     Do not specify any FILE on the command line when using this option.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: sum invocation,  Next: cksum invocation,  Prev: wc invocation,  Up: Summarizing files

6.2 `sum': Print checksum and block counts
==========================================

`sum' computes a 16-bit checksum for each given FILE, or standard input
if none are given or for a FILE of `-'.  Synopsis:

     sum [OPTION]... [FILE]...

   `sum' prints the checksum for each FILE followed by the number of
blocks in the file (rounded up).  If more than one FILE is given, file
names are also printed (by default).  (With the `--sysv' option,
corresponding file names are printed when there is at least one file
argument.)

   By default, GNU `sum' computes checksums using an algorithm
compatible with BSD `sum' and prints file sizes in units of 1024-byte
blocks.

   The program accepts the following options.  Also see *Note Common
options::.

`-r'
     Use the default (BSD compatible) algorithm.  This option is
     included for compatibility with the System V `sum'.  Unless `-s'
     was also given, it has no effect.

`-s'
`--sysv'
     Compute checksums using an algorithm compatible with System V
     `sum''s default, and print file sizes in units of 512-byte blocks.


   `sum' is provided for compatibility; the `cksum' program (see next
section) is preferable in new applications.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: cksum invocation,  Next: md5sum invocation,  Prev: sum invocation,  Up: Summarizing files

6.3 `cksum': Print CRC checksum and byte counts
===============================================

`cksum' computes a cyclic redundancy check (CRC) checksum for each
given FILE, or standard input if none are given or for a FILE of `-'.
Synopsis:

     cksum [OPTION]... [FILE]...

   `cksum' prints the CRC checksum for each file along with the number
of bytes in the file, and the file name unless no arguments were given.

   `cksum' is typically used to ensure that files transferred by
unreliable means (e.g., netnews) have not been corrupted, by comparing
the `cksum' output for the received files with the `cksum' output for
the original files (typically given in the distribution).

   The CRC algorithm is specified by the POSIX standard.  It is not
compatible with the BSD or System V `sum' algorithms (see the previous
section); it is more robust.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: md5sum invocation,  Next: sha1sum invocation,  Prev: cksum invocation,  Up: Summarizing files

6.4 `md5sum': Print or check MD5 digests
========================================

`md5sum' computes a 128-bit checksum (or "fingerprint" or
"message-digest") for each specified FILE.

   Note: The MD5 digest is more reliable than a simple CRC (provided by
the `cksum' command) for detecting accidental file corruption, as the
chances of accidentally having two files with identical MD5 are
vanishingly small.  However, it should not be considered truly secure
against malicious tampering: although finding a file with a given MD5
fingerprint, or modifying a file so as to retain its MD5 are considered
infeasible at the moment, it is known how to produce different files
with identical MD5 (a "collision"), something which can be a security
issue in certain contexts.  For more secure hashes, consider using
SHA-1 or SHA-2.  *Note sha1sum invocation::, and *Note sha2 utilities::.

   If a FILE is specified as `-' or if no files are given `md5sum'
computes the checksum for the standard input.  `md5sum' can also
determine whether a file and checksum are consistent.  Synopsis:

     md5sum [OPTION]... [FILE]...

   For each FILE, `md5sum' outputs the MD5 checksum, a flag indicating
a binary or text input file, and the file name.  If FILE contains a
backslash or newline, the line is started with a backslash, and each
problematic character in the file name is escaped with a backslash,
making the output unambiguous even in the presence of arbitrary file
names.  If FILE is omitted or specified as `-', standard input is read.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--binary'
     Treat each input file as binary, by reading it in binary mode and
     outputting a `*' flag.  This is the inverse of `--text'.  On
     systems like GNU that do not distinguish between binary and text
     files, this option merely flags each input file as binary: the MD5
     checksum is unaffected.  This option is the default on systems
     like MS-DOS that distinguish between binary and text files, except
     for reading standard input when standard input is a terminal.

`-c'
`--check'
     Read file names and checksum information (not data) from each FILE
     (or from stdin if no FILE was specified) and report whether the
     checksums match the contents of the named files.  The input to
     this mode of `md5sum' is usually the output of a prior,
     checksum-generating run of `md5sum'.  Each valid line of input
     consists of an MD5 checksum, a binary/text flag, and then a file
     name.  Binary files are marked with `*', text with ` '.  For each
     such line, `md5sum' reads the named file and computes its MD5
     checksum.  Then, if the computed message digest does not match the
     one on the line with the file name, the file is noted as having
     failed the test.  Otherwise, the file passes the test.  By
     default, for each valid line, one line is written to standard
     output indicating whether the named file passed the test.  After
     all checks have been performed, if there were any failures, a
     warning is issued to standard error.  Use the `--status' option to
     inhibit that output.  If any listed file cannot be opened or read,
     if any valid line has an MD5 checksum inconsistent with the
     associated file, or if no valid line is found, `md5sum' exits with
     nonzero status.  Otherwise, it exits successfully.

`--status'
     This option is useful only when verifying checksums.  When
     verifying checksums, don't generate the default one-line-per-file
     diagnostic and don't output the warning summarizing any failures.
     Failures to open or read a file still evoke individual diagnostics
     to standard error.  If all listed files are readable and are
     consistent with the associated MD5 checksums, exit successfully.
     Otherwise exit with a status code indicating there was a failure.

`-t'
`--text'
     Treat each input file as text, by reading it in text mode and
     outputting a ` ' flag.  This is the inverse of `--binary'.  This
     option is the default on systems like GNU that do not distinguish
     between binary and text files.  On other systems, it is the
     default for reading standard input when standard input is a
     terminal.

`-w'
`--warn'
     When verifying checksums, warn about improperly formatted MD5
     checksum lines.  This option is useful only if all but a few lines
     in the checked input are valid.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: sha1sum invocation,  Next: sha2 utilities,  Prev: md5sum invocation,  Up: Summarizing files

6.5 `sha1sum': Print or check SHA-1 digests
===========================================

`sha1sum' computes a 160-bit checksum for each specified FILE.  The
usage and options of this command are precisely the same as for
`md5sum'.  *Note md5sum invocation::.

   Note: The SHA-1 digest is more secure than MD5, and no collisions of
it are known (different files having the same fingerprint).  However,
it is known that they can be produced with considerable, but not
unreasonable, resources.  For this reason, it is generally considered
that SHA-1 should be gradually phased out in favor of the more secure
SHA-2 hash algorithms.  *Note sha2 utilities::.


File: coreutils.info,  Node: sha2 utilities,  Prev: sha1sum invocation,  Up: Summarizing files

6.6 sha2 utilities: Print or check SHA-2 digests
================================================

The commands `sha224sum', `sha256sum', `sha384sum' and `sha512sum'
compute checksums of various lengths (respectively 224, 256, 384 and
512 bits), collectively known as the SHA-2 hashes.  The usage and
options of these commands are precisely the same as for `md5sum'.
*Note md5sum invocation::.

   Note: The SHA384 and SHA512 digests are considerably slower to
compute, especially on 32-bit computers, than SHA224 or SHA256.


File: coreutils.info,  Node: Operating on sorted files,  Next: Operating on fields within a line,  Prev: Summarizing files,  Up: Top

7 Operating on sorted files
***************************

These commands work with (or produce) sorted files.

* Menu:

* sort invocation::             Sort text files.
* shuf invocation::             Shuffle text files.
* uniq invocation::             Uniquify files.
* comm invocation::             Compare two sorted files line by line.
* ptx invocation::              Produce a permuted index of file contents.
* tsort invocation::            Topological sort.
* tsort background::            Where tsort came from.


File: coreutils.info,  Node: sort invocation,  Next: shuf invocation,  Up: Operating on sorted files

7.1 `sort': Sort text files
===========================

`sort' sorts, merges, or compares all the lines from the given files,
or standard input if none are given or for a FILE of `-'.  By default,
`sort' writes the results to standard output.  Synopsis:

     sort [OPTION]... [FILE]...

   `sort' has three modes of operation: sort (the default), merge, and
check for sortedness.  The following options change the operation mode:

`-c'
`--check'
`--check=diagnose-first'
     Check whether the given file is already sorted: if it is not all
     sorted, print a diagnostic containing the first out-of-order line
     and exit with a status of 1.  Otherwise, exit successfully.  At
     most one input file can be given.

`-C'
`--check=quiet'
`--check=silent'
     Exit successfully if the given file is already sorted, and exit
     with status 1 otherwise.  At most one input file can be given.
     This is like `-c', except it does not print a diagnostic.

`-m'
`--merge'
     Merge the given files by sorting them as a group.  Each input file
     must always be individually sorted.  It always works to sort
     instead of merge; merging is provided because it is faster, in the
     case where it works.


   A pair of lines is compared as follows: `sort' compares each pair of
fields, in the order specified on the command line, according to the
associated ordering options, until a difference is found or no fields
are left.  If no key fields are specified, `sort' uses a default key of
the entire line.  Finally, as a last resort when all keys compare
equal, `sort' compares entire lines as if no ordering options other
than `--reverse' (`-r') were specified.  The `--stable' (`-s') option
disables this "last-resort comparison" so that lines in which all
fields compare equal are left in their original relative order.  The
`--unique' (`-u') option also disables the last-resort comparison.

   Unless otherwise specified, all comparisons use the character
collating sequence specified by the `LC_COLLATE' locale.(1)

   GNU `sort' (as specified for all GNU utilities) has no limit on
input line length or restrictions on bytes allowed within lines.  In
addition, if the final byte of an input file is not a newline, GNU
`sort' silently supplies one.  A line's trailing newline is not part of
the line for comparison purposes.

   Exit status:

     0 if no error occurred
     1 if invoked with `-c' or `-C' and the input is not sorted
     2 if an error occurred

   If the environment variable `TMPDIR' is set, `sort' uses its value
as the directory for temporary files instead of `/tmp'.  The
`--temporary-directory' (`-T') option in turn overrides the environment
variable.

   The following options affect the ordering of output lines.  They may
be specified globally or as part of a specific key field.  If no key
fields are specified, global options apply to comparison of entire
lines; otherwise the global options are inherited by key fields that do
not specify any special options of their own.  In pre-POSIX versions of
`sort', global options affect only later key fields, so portable shell
scripts should specify global options first.

`-b'
`--ignore-leading-blanks'
     Ignore leading blanks when finding sort keys in each line.  By
     default a blank is a space or a tab, but the `LC_CTYPE' locale can
     change this.

`-d'
`--dictionary-order'
     Sort in "phone directory" order: ignore all characters except
     letters, digits and blanks when sorting.  By default letters and
     digits are those of ASCII and a blank is a space or a tab, but the
     `LC_CTYPE' locale can change this.

`-f'
`--ignore-case'
     Fold lowercase characters into the equivalent uppercase characters
     when comparing so that, for example, `b' and `B' sort as equal.
     The `LC_CTYPE' locale determines character types.

`-g'
`--general-numeric-sort'
     Sort numerically, using the standard C function `strtod' to convert
     a prefix of each line to a double-precision floating point number.
     This allows floating point numbers to be specified in scientific
     notation, like `1.0e-34' and `10e100'.  The `LC_NUMERIC' locale
     determines the decimal-point character.  Do not report overflow,
     underflow, or conversion errors.  Use the following collating
     sequence:

        * Lines that do not start with numbers (all considered to be
          equal).

        * NaNs ("Not a Number" values, in IEEE floating point
          arithmetic) in a consistent but machine-dependent order.

        * Minus infinity.

        * Finite numbers in ascending numeric order (with -0 and +0
          equal).

        * Plus infinity.

     Use this option only if there is no alternative; it is much slower
     than `--numeric-sort' (`-n') and it can lose information when
     converting to floating point.

`-i'
`--ignore-nonprinting'
     Ignore nonprinting characters.  The `LC_CTYPE' locale determines
     character types.  This option has no effect if the stronger
     `--dictionary-order' (`-d') option is also given.

`-M'
`--month-sort'
     An initial string, consisting of any amount of blanks, followed by
     a month name abbreviation, is folded to UPPER case and compared in
     the order `JAN' < `FEB' < ... < `DEC'.  Invalid names compare low
     to valid names.  The `LC_TIME' locale category determines the
     month spellings.  By default a blank is a space or a tab, but the
     `LC_CTYPE' locale can change this.

`-n'
`--numeric-sort'
     Sort numerically.  The number begins each line and consists of
     optional blanks, an optional `-' sign, and zero or more digits
     possibly separated by thousands separators, optionally followed by
     a decimal-point character and zero or more digits.  An empty
     number is treated as `0'.  The `LC_NUMERIC' locale specifies the
     decimal-point character and thousands separator.  By default a
     blank is a space or a tab, but the `LC_CTYPE' locale can change
     this.

     Comparison is exact; there is no rounding error.

     Neither a leading `+' nor exponential notation is recognized.  To
     compare such strings numerically, use the `--general-numeric-sort'
     (`-g') option.

`-r'
`--reverse'
     Reverse the result of comparison, so that lines with greater key
     values appear earlier in the output instead of later.

`-R'
`--random-sort'
     Sort by hashing the input keys and then sorting the hash values.
     Choose the hash function at random, ensuring that it is free of
     collisions so that differing keys have differing hash values.
     This is like a random permutation of the inputs (*note shuf
     invocation::), except that keys with the same value sort together.

     If multiple random sort fields are specified, the same random hash
     function is used for all fields.  To use different random hash
     functions for different fields, you can invoke `sort' more than
     once.

     The choice of hash function is affected by the `--random-source'
     option.


   Other options are:

`--compress-program=PROG'
     Compress any temporary files with the program PROG.

     With no arguments, PROG must compress standard input to standard
     output, and when given the `-d' option it must decompress standard
     input to standard output.

     Terminate with an error if PROG exits with nonzero status.

     Whitespace and the backslash character should not appear in PROG;
     they are reserved for future use.

`-k POS1[,POS2]'
`--key=POS1[,POS2]'
     Specify a sort field that consists of the part of the line between
     POS1 and POS2 (or the end of the line, if POS2 is omitted),
     _inclusive_.

     Each POS has the form `F[.C][OPTS]', where F is the number of the
     field to use, and C is the number of the first character from the
     beginning of the field.  Fields and character positions are
     numbered starting with 1; a character position of zero in POS2
     indicates the field's last character.  If `.C' is omitted from
     POS1, it defaults to 1 (the beginning of the field); if omitted
     from POS2, it defaults to 0 (the end of the field).  OPTS are
     ordering options, allowing individual keys to be sorted according
     to different rules; see below for details.  Keys can span multiple
     fields.

     Example:  To sort on the second field, use `--key=2,2' (`-k 2,2').
     See below for more examples.

`-o OUTPUT-FILE'
`--output=OUTPUT-FILE'
     Write output to OUTPUT-FILE instead of standard output.  Normally,
     `sort' reads all input before opening OUTPUT-FILE, so you can
     safely sort a file in place by using commands like `sort -o F F'
     and `cat F | sort -o F'.  However, `sort' with `--merge' (`-m')
     can open the output file before reading all input, so a command
     like `cat F | sort -m -o F - G' is not safe as `sort' might start
     writing `F' before `cat' is done reading it.

     On newer systems, `-o' cannot appear after an input file if
     `POSIXLY_CORRECT' is set, e.g., `sort F -o F'.  Portable scripts
     should specify `-o OUTPUT-FILE' before any input files.

`--random-source=FILE'
     Use FILE as a source of random data used to determine which random
     hash function to use with the `-R' option.  *Note Random sources::.

`-s'
`--stable'
     Make `sort' stable by disabling its last-resort comparison.  This
     option has no effect if no fields or global ordering options other
     than `--reverse' (`-r') are specified.

`-S SIZE'
`--buffer-size=SIZE'
     Use a main-memory sort buffer of the given SIZE.  By default, SIZE
     is in units of 1024 bytes.  Appending `%' causes SIZE to be
     interpreted as a percentage of physical memory.  Appending `K'
     multiplies SIZE by 1024 (the default), `M' by 1,048,576, `G' by
     1,073,741,824, and so on for `T', `P', `E', `Z', and `Y'.
     Appending `b' causes SIZE to be interpreted as a byte count, with
     no multiplication.

     This option can improve the performance of `sort' by causing it to
     start with a larger or smaller sort buffer than the default.
     However, this option affects only the initial buffer size.  The
     buffer grows beyond SIZE if `sort' encounters input lines larger
     than SIZE.

`-t SEPARATOR'
`--field-separator=SEPARATOR'
     Use character SEPARATOR as the field separator when finding the
     sort keys in each line.  By default, fields are separated by the
     empty string between a non-blank character and a blank character.
     By default a blank is a space or a tab, but the `LC_CTYPE' locale
     can change this.

     That is, given the input line ` foo bar', `sort' breaks it into
     fields ` foo' and ` bar'.  The field separator is not considered
     to be part of either the field preceding or the field following,
     so with `sort -t " "' the same input line has three fields: an
     empty field, `foo', and `bar'.  However, fields that extend to the
     end of the line, as `-k 2', or fields consisting of a range, as
     `-k 2,3', retain the field separators present between the
     endpoints of the range.

     To specify a null character (ASCII NUL) as the field separator,
     use the two-character string `\0', e.g., `sort -t '\0''.

`-T TEMPDIR'
`--temporary-directory=TEMPDIR'
     Use directory TEMPDIR to store temporary files, overriding the
     `TMPDIR' environment variable.  If this option is given more than
     once, temporary files are stored in all the directories given.  If
     you have a large sort or merge that is I/O-bound, you can often
     improve performance by using this option to specify directories on
     different disks and controllers.

`-u'
`--unique'
     Normally, output only the first of a sequence of lines that compare
     equal.  For the `--check' (`-c' or `-C') option, check that no
     pair of consecutive lines compares equal.

     This option also disables the default last-resort comparison.

     The commands `sort -u' and `sort | uniq' are equivalent, but this
     equivalence does not extend to arbitrary `sort' options.  For
     example, `sort -n -u' inspects only the value of the initial
     numeric string when checking for uniqueness, whereas `sort -n |
     uniq' inspects the entire line.  *Note uniq invocation::.

`-z'
`--zero-terminated'
     Treat the input as a set of lines, each terminated by a null
     character (ASCII NUL) instead of a line feed (ASCII LF).  This
     option can be useful in conjunction with `perl -0' or `find
     -print0' and `xargs -0' which do the same in order to reliably
     handle arbitrary file names (even those containing blanks or other
     special characters).


   Historical (BSD and System V) implementations of `sort' have
differed in their interpretation of some options, particularly `-b',
`-f', and `-n'.  GNU sort follows the POSIX behavior, which is usually
(but not always!) like the System V behavior.  According to POSIX, `-n'
no longer implies `-b'.  For consistency, `-M' has been changed in the
same way.  This may affect the meaning of character positions in field
specifications in obscure cases.  The only fix is to add an explicit
`-b'.

   A position in a sort field specified with `-k' may have any of the
option letters `Mbdfinr' appended to it, in which case the global
ordering options are not used for that particular field.  The `-b'
option may be independently attached to either or both of the start and
end positions of a field specification, and if it is inherited from the
global options it will be attached to both.  If input lines can contain
leading or adjacent blanks and `-t' is not used, then `-k' is typically
combined with `-b', `-g', `-M', or `-n'; otherwise the varying numbers
of leading blanks in fields can cause confusing results.

   If the start position in a sort field specifier falls after the end
of the line or after the end field, the field is empty.  If the `-b'
option was specified, the `.C' part of a field specification is counted
from the first nonblank character of the field.

   On older systems, `sort' supports an obsolete origin-zero syntax
`+POS1 [-POS2]' for specifying sort keys.  This obsolete behavior can
be enabled or disabled with the `_POSIX2_VERSION' environment variable
(*note Standards conformance::); it can also be enabled when
`POSIXLY_CORRECT' is not set by using the obsolete syntax with `-POS2'
present.

   Scripts intended for use on standard hosts should avoid obsolete
syntax and should use `-k' instead.  For example, avoid `sort +2',
since it might be interpreted as either `sort ./+2' or `sort -k 3'.  If
your script must also run on hosts that support only the obsolete
syntax, it can use a test like `if sort -k 1 </dev/null >/dev/null
2>&1; then ...' to decide which syntax to use.

   Here are some examples to illustrate various combinations of options.

   * Sort in descending (reverse) numeric order.

          sort -n -r

   * Sort alphabetically, omitting the first and second fields and the
     blanks at the start of the third field.  This uses a single key
     composed of the characters beginning at the start of the first
     nonblank character in field three and extending to the end of each
     line.

          sort -k 3b

   * Sort numerically on the second field and resolve ties by sorting
     alphabetically on the third and fourth characters of field five.
     Use `:' as the field delimiter.

          sort -t : -k 2,2n -k 5.3,5.4

     Note that if you had written `-k 2n' instead of `-k 2,2n' `sort'
     would have used all characters beginning in the second field and
     extending to the end of the line as the primary _numeric_ key.
     For the large majority of applications, treating keys spanning
     more than one field as numeric will not do what you expect.

     Also note that the `n' modifier was applied to the field-end
     specifier for the first key.  It would have been equivalent to
     specify `-k 2n,2' or `-k 2n,2n'.  All modifiers except `b' apply
     to the associated _field_, regardless of whether the modifier
     character is attached to the field-start and/or the field-end part
     of the key specifier.

   * Sort the password file on the fifth field and ignore any leading
     blanks.  Sort lines with equal values in field five on the numeric
     user ID in field three.  Fields are separated by `:'.

          sort -t : -k 5b,5 -k 3,3n /etc/passwd
          sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
          sort -t : -b -k 5,5 -k 3,3n /etc/passwd

     These three commands have equivalent effect.  The first specifies
     that the first key's start position ignores leading blanks and the
     second key is sorted numerically.  The other two commands rely on
     global options being inherited by sort keys that lack modifiers.
     The inheritance works in this case because `-k 5b,5b' and `-k
     5b,5' are equivalent, as the location of a field-end lacking a `.C'
     character position is not affected by whether initial blanks are
     skipped.

   * Sort a set of log files, primarily by IPv4 address and secondarily
     by time stamp.  If two lines' primary and secondary keys are
     identical, output the lines in the same order that they were
     input.  The log files contain lines that look like this:

          4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
          211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2

     Fields are separated by exactly one space.  Sort IPv4 addresses
     lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
     because 61 is less than 129.

          sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
          sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n

     This example cannot be done with a single `sort' invocation, since
     IPv4 address components are separated by `.' while dates come just
     after a space.  So it is broken down into two invocations of
     `sort': the first sorts by time stamp and the second by IPv4
     address.  The time stamp is sorted by year, then month, then day,
     and finally by hour-minute-second field, using `-k' to isolate each
     field.  Except for hour-minute-second there's no need to specify
     the end of each key field, since the `n' and `M' modifiers sort
     based on leading prefixes that cannot cross field boundaries.  The
     IPv4 addresses are sorted lexicographically.  The second sort uses
     `-s' so that ties in the primary key are broken by the secondary
     key; the first sort uses `-s' so that the combination of the two
     sorts is stable.

   * Generate a tags file in case-insensitive sorted order.

          find src -type f -print0 | sort -z -f | xargs -0 etags --append

     The use of `-print0', `-z', and `-0' in this case means that file
     names that contain blanks or other special characters are not
     broken up by the sort operation.

   * Shuffle a list of directories, but preserve the order of files
     within each directory.  For instance, one could use this to
     generate a music playlist in which albums are shuffled but the
     songs of each album are played in order.

          ls */* | sort -t / -k 1,1R -k 2,2


   ---------- Footnotes ----------

   (1) If you use a non-POSIX locale (e.g., by setting `LC_ALL' to
`en_US'), then `sort' may produce output that is sorted differently
than you're accustomed to.  In that case, set the `LC_ALL' environment
variable to `C'.  Note that setting only `LC_COLLATE' has two problems.
First, it is ineffective if `LC_ALL' is also set.  Second, it has
undefined behavior if `LC_CTYPE' (or `LANG', if `LC_CTYPE' is unset) is
set to an incompatible value.  For example, you get undefined behavior
if `LC_CTYPE' is `ja_JP.PCK' but `LC_COLLATE' is `en_US.UTF-8'.


File: coreutils.info,  Node: shuf invocation,  Next: uniq invocation,  Prev: sort invocation,  Up: Operating on sorted files

7.2 `shuf': Shuffling text
==========================

`shuf' shuffles its input by outputting a random permutation of its
input lines.  Each output permutation is equally likely.  Synopses:

     shuf [OPTION]... [FILE]
     shuf -e [OPTION]... [ARG]...
     shuf -i LO-HI [OPTION]...

   `shuf' has three modes of operation that affect where it obtains its
input lines.  By default, it reads lines from standard input.  The
following options change the operation mode:

`-e'
`--echo'
     Treat each command-line operand as an input line.

`-i LO-HI'
`--input-range=LO-HI'
     Act as if input came from a file containing the range of unsigned
     decimal integers LO...HI, one per line.


   `shuf''s other options can affect its behavior in all operation
modes:

`-n LINES'
`--head-lines=LINES'
     Output at most LINES lines.  By default, all input lines are
     output.

`-o OUTPUT-FILE'
`--output=OUTPUT-FILE'
     Write output to OUTPUT-FILE instead of standard output.  `shuf'
     reads all input before opening OUTPUT-FILE, so you can safely
     shuffle a file in place by using commands like `shuf -o F <F' and
     `cat F | shuf -o F'.

`--random-source=FILE'
     Use FILE as a source of random data used to determine which
     permutation to generate.  *Note Random sources::.

`-z'
`--zero-terminated'
     Treat the input and output as a set of lines, each terminated by a
     zero byte (ASCII NUL (Null) character) instead of an ASCII LF
     (Line Feed).  This option can be useful in conjunction with `perl
     -0' or `find -print0' and `xargs -0' which do the same in order to
     reliably handle arbitrary file names (even those containing blanks
     or other special characters).


   For example:

     shuf <<EOF
     A man,
     a plan,
     a canal:
     Panama!
     EOF

might produce the output

     Panama!
     A man,
     a canal:
     a plan,

Similarly, the command:

     shuf -e clubs hearts diamonds spades

might output:

     clubs
     diamonds
     spades
     hearts

and the command `shuf -i 1-4' might output:

     4
     2
     1
     3

These examples all have four input lines, so `shuf' might produce any
of the twenty-four possible permutations of the input.  In general, if
there are N input lines, there are N! (i.e., N factorial, or N * (N -
1) * ... * 1) possible output permutations.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: uniq invocation,  Next: comm invocation,  Prev: shuf invocation,  Up: Operating on sorted files

7.3 `uniq': Uniquify files
==========================

`uniq' writes the unique lines in the given `input', or standard input
if nothing is given or for an INPUT name of `-'.  Synopsis:

     uniq [OPTION]... [INPUT [OUTPUT]]

   By default, `uniq' prints its input lines, except that it discards
all but the first of adjacent repeated lines, so that no output lines
are repeated.  Optionally, it can instead discard lines that are not
repeated, or all repeated lines.

   The input need not be sorted, but repeated input lines are detected
only if they are adjacent.  If you want to discard non-adjacent
duplicate lines, perhaps you want to use `sort -u'.  *Note sort
invocation::.

   Comparisons use the character collating sequence specified by the
`LC_COLLATE' locale category.

   If no OUTPUT file is specified, `uniq' writes to standard output.

   The program accepts the following options.  Also see *Note Common
options::.

`-f N'
`--skip-fields=N'
     Skip N fields on each line before checking for uniqueness.  Use a
     null string for comparison if a line has fewer than N fields.
     Fields are sequences of non-space non-tab characters that are
     separated from each other by at least one space or tab.

     For compatibility `uniq' supports an obsolete option syntax `-N'.
     New scripts should use `-f N' instead.

`-s N'
`--skip-chars=N'
     Skip N characters before checking for uniqueness.  Use a null
     string for comparison if a line has fewer than N characters.  If
     you use both the field and character skipping options, fields are
     skipped over first.

     On older systems, `uniq' supports an obsolete option syntax `+N'.
     This obsolete behavior can be enabled or disabled with the
     `_POSIX2_VERSION' environment variable (*note Standards
     conformance::), but portable scripts should avoid commands whose
     behavior depends on this variable.  For example, use `uniq ./+10'
     or `uniq -s 10' rather than the ambiguous `uniq +10'.

`-c'
`--count'
     Print the number of times each line occurred along with the line.

`-i'
`--ignore-case'
     Ignore differences in case when comparing lines.

`-d'
`--repeated'
     Discard lines that are not repeated.  When used by itself, this
     option causes `uniq' to print the first copy of each repeated line,
     and nothing else.

`-D'
`--all-repeated[=DELIMIT-METHOD]'
     Do not discard the second and subsequent repeated input lines, but
     discard lines that are not repeated.  This option is useful mainly
     in conjunction with other options e.g., to ignore case or to
     compare only selected fields.  The optional DELIMIT-METHOD tells
     how to delimit groups of repeated lines, and must be one of the
     following:

    `none'
          Do not delimit groups of repeated lines.  This is equivalent
          to `--all-repeated' (`-D').

    `prepend'
          Output a newline before each group of repeated lines.

    `separate'
          Separate groups of repeated lines with a single newline.
          This is the same as using `prepend', except that there is no
          newline before the first group, and hence may be better
          suited for output direct to users.

     Note that when groups are delimited and the input stream contains
     two or more consecutive blank lines, then the output is ambiguous.
     To avoid that, filter the input through `tr -s '\n'' to replace
     each sequence of consecutive newlines with a single newline.

     This is a GNU extension.

`-u'
`--unique'
     Discard the first repeated line.  When used by itself, this option
     causes `uniq' to print unique lines, and nothing else.

`-w N'
`--check-chars=N'
     Compare at most N characters on each line (after skipping any
     specified fields and characters).  By default the entire rest of
     the lines are compared.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: comm invocation,  Next: ptx invocation,  Prev: uniq invocation,  Up: Operating on sorted files

7.4 `comm': Compare two sorted files line by line
=================================================

`comm' writes to standard output lines that are common, and lines that
are unique, to two input files; a file name of `-' means standard
input.  Synopsis:

     comm [OPTION]... FILE1 FILE2

   Before `comm' can be used, the input files must be sorted using the
collating sequence specified by the `LC_COLLATE' locale.  If an input
file ends in a non-newline character, a newline is silently appended.
The `sort' command with no options always outputs a file that is
suitable input to `comm'.

   With no options, `comm' produces three-column output.  Column one
contains lines unique to FILE1, column two contains lines unique to
FILE2, and column three contains lines common to both files.  Columns
are separated by a single TAB character.

   The options `-1', `-2', and `-3' suppress printing of the
corresponding columns.  Also see *Note Common options::.

   Unlike some other comparison utilities, `comm' has an exit status
that does not depend on the result of the comparison.  Upon normal
completion `comm' produces an exit code of zero.  If there is an error
it exits with nonzero status.


File: coreutils.info,  Node: tsort invocation,  Next: tsort background,  Prev: ptx invocation,  Up: Operating on sorted files

7.5 `tsort': Topological sort
=============================

`tsort' performs a topological sort on the given FILE, or standard
input if no input file is given or for a FILE of `-'.  For more details
and some history, see *Note tsort background::.  Synopsis:

     tsort [OPTION] [FILE]

   `tsort' reads its input as pairs of strings, separated by blanks,
indicating a partial ordering.  The output is a total ordering that
corresponds to the given partial ordering.

   For example

     tsort <<EOF
     a b c
     d
     e f
     b c d e
     EOF

will produce the output

     a
     b
     c
     d
     e
     f

   Consider a more realistic example.  You have a large set of
functions all in one file, and they may all be declared static except
one.  Currently that one (say `main') is the first function defined in
the file, and the ones it calls directly follow it, followed by those
they call, etc.  Let's say that you are determined to take advantage of
prototypes, so you have to choose between declaring all of those
functions (which means duplicating a lot of information from the
definitions) and rearranging the functions so that as many as possible
are defined before they are used.  One way to automate the latter
process is to get a list for each function of the functions it calls
directly.  Many programs can generate such lists.  They describe a call
graph.  Consider the following list, in which a given line indicates
that the function on the left calls the one on the right directly.

     main parse_options
     main tail_file
     main tail_forever
     tail_file pretty_name
     tail_file write_header
     tail_file tail
     tail_forever recheck
     tail_forever pretty_name
     tail_forever write_header
     tail_forever dump_remainder
     tail tail_lines
     tail tail_bytes
     tail_lines start_lines
     tail_lines dump_remainder
     tail_lines file_lines
     tail_lines pipe_lines
     tail_bytes xlseek
     tail_bytes start_bytes
     tail_bytes dump_remainder
     tail_bytes pipe_bytes
     file_lines dump_remainder
     recheck pretty_name

   then you can use `tsort' to produce an ordering of those functions
that satisfies your requirement.

     example$ tsort call-graph | tac
     dump_remainder
     start_lines
     file_lines
     pipe_lines
     xlseek
     start_bytes
     pipe_bytes
     tail_lines
     tail_bytes
     pretty_name
     write_header
     tail
     recheck
     parse_options
     tail_file
     tail_forever
     main

   `tsort' detects any cycles in the input and writes the first cycle
encountered to standard error.

   Note that for a given partial ordering, generally there is no unique
total ordering.  In the context of the call graph above, the function
`parse_options' may be placed anywhere in the list as long as it
precedes `main'.

   The only options are `--help' and `--version'.  *Note Common
options::.


File: coreutils.info,  Node: tsort background,  Prev: tsort invocation,  Up: Operating on sorted files

7.6 `tsort': Background
=======================

`tsort' exists because very early versions of the Unix linker processed
an archive file exactly once, and in order.  As `ld' read each object
in the archive, it decided whether it was needed in the program based on
whether it defined any symbols which were undefined at that point in
the link.

   This meant that dependencies within the archive had to be handled
specially.  For example, `scanf' probably calls `read'.  That means
that in a single pass through an archive, it was important for `scanf.o'
to appear before read.o, because otherwise a program which calls
`scanf' but not `read' might end up with an unexpected unresolved
reference to `read'.

   The way to address this problem was to first generate a set of
dependencies of one object file on another.  This was done by a shell
script called `lorder'.  The GNU tools don't provide a version of
lorder, as far as I know, but you can still find it in BSD
distributions.

   Then you ran `tsort' over the `lorder' output, and you used the
resulting sort to define the order in which you added objects to the
archive.

   This whole procedure has been obsolete since about 1980, because
Unix archives now contain a symbol table (traditionally built by
`ranlib', now generally built by `ar' itself), and the Unix linker uses
the symbol table to effectively make multiple passes over an archive
file.

   Anyhow, that's where tsort came from.  To solve an old problem with
the way the linker handled archive files, which has since been solved
in different ways.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: ptx invocation,  Next: tsort invocation,  Prev: comm invocation,  Up: Operating on sorted files

7.7 `ptx': Produce permuted indexes
===================================

`ptx' reads a text file and essentially produces a permuted index, with
each keyword in its context.  The calling sketch is either one of:

     ptx [OPTION ...] [FILE ...]
     ptx -G [OPTION ...] [INPUT [OUTPUT]]

   The `-G' (or its equivalent: `--traditional') option disables all
GNU extensions and reverts to traditional mode, thus introducing some
limitations and changing several of the program's default option values.
When `-G' is not specified, GNU extensions are always enabled.  GNU
extensions to `ptx' are documented wherever appropriate in this
document.  For the full list, see *Note Compatibility in ptx::.

   Individual options are explained in the following sections.

   When GNU extensions are enabled, there may be zero, one or several
FILEs after the options.  If there is no FILE, the program reads the
standard input.  If there is one or several FILEs, they give the name
of input files which are all read in turn, as if all the input files
were concatenated.  However, there is a full contextual break between
each file and, when automatic referencing is requested, file names and
line numbers refer to individual text input files.  In all cases, the
program outputs the permuted index to the standard output.

   When GNU extensions are _not_ enabled, that is, when the program
operates in traditional mode, there may be zero, one or two parameters
besides the options.  If there are no parameters, the program reads the
standard input and outputs the permuted index to the standard output.
If there is only one parameter, it names the text INPUT to be read
instead of the standard input.  If two parameters are given, they give
respectively the name of the INPUT file to read and the name of the
OUTPUT file to produce.  _Be very careful_ to note that, in this case,
the contents of file given by the second parameter is destroyed.  This
behavior is dictated by System V `ptx' compatibility; GNU Standards
normally discourage output parameters not introduced by an option.

   Note that for _any_ file named as the value of an option or as an
input text file, a single dash `-' may be used, in which case standard
input is assumed.  However, it would not make sense to use this
convention more than once per program invocation.

* Menu:

* General options in ptx::      Options which affect general program behavior.
* Charset selection in ptx::    Underlying character set considerations.
* Input processing in ptx::     Input fields, contexts, and keyword selection.
* Output formatting in ptx::    Types of output format, and sizing the fields.
* Compatibility in ptx::


File: coreutils.info,  Node: General options in ptx,  Next: Charset selection in ptx,  Up: ptx invocation

7.7.1 General options
---------------------

`-G'
`--traditional'
     As already explained, this option disables all GNU extensions to
     `ptx' and switches to traditional mode.

`--help'
     Print a short help on standard output, then exit without further
     processing.

`--version'
     Print the program version on standard output, then exit without
     further processing.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Charset selection in ptx,  Next: Input processing in ptx,  Prev: General options in ptx,  Up: ptx invocation

7.7.2 Charset selection
-----------------------

As it is set up now, the program assumes that the input file is coded
using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
_unless_ it is compiled for MS-DOS, in which case it uses the character
set of the IBM-PC.  (GNU `ptx' is not known to work on smaller MS-DOS
machines anymore.)  Compared to 7-bit ASCII, the set of characters
which are letters is different; this alters the behavior of regular
expression matching.  Thus, the default regular expression for a
keyword allows foreign or diacriticized letters.  Keyword sorting,
however, is still crude; it obeys the underlying character set ordering
quite blindly.

`-f'
`--ignore-case'
     Fold lower case letters to upper case for sorting.



File: coreutils.info,  Node: Input processing in ptx,  Next: Output formatting in ptx,  Prev: Charset selection in ptx,  Up: ptx invocation

7.7.3 Word selection and input processing
-----------------------------------------

`-b FILE'
`--break-file=FILE'
     This option provides an alternative (to `-W') method of describing
     which characters make up words.  It introduces the name of a file
     which contains a list of characters which can_not_ be part of one
     word; this file is called the "Break file".  Any character which
     is not part of the Break file is a word constituent.  If both
     options `-b' and `-W' are specified, then `-W' has precedence and
     `-b' is ignored.

     When GNU extensions are enabled, the only way to avoid newline as a
     break character is to write all the break characters in the file
     with no newline at all, not even at the end of the file.  When GNU
     extensions are disabled, spaces, tabs and newlines are always
     considered as break characters even if not included in the Break
     file.

`-i FILE'
`--ignore-file=FILE'
     The file associated with this option contains a list of words
     which will never be taken as keywords in concordance output.  It
     is called the "Ignore file".  The file contains exactly one word
     in each line; the end of line separation of words is not subject
     to the value of the `-S' option.

`-o FILE'
`--only-file=FILE'
     The file associated with this option contains a list of words
     which will be retained in concordance output; any word not
     mentioned in this file is ignored.  The file is called the "Only
     file".  The file contains exactly one word in each line; the end
     of line separation of words is not subject to the value of the
     `-S' option.

     There is no default for the Only file.  When both an Only file and
     an Ignore file are specified, a word is considered a keyword only
     if it is listed in the Only file and not in the Ignore file.

`-r'
`--references'
     On each input line, the leading sequence of non-white space
     characters will be taken to be a reference that has the purpose of
     identifying this input line in the resulting permuted index.  For
     more information about reference production, see *Note Output
     formatting in ptx::.  Using this option changes the default value
     for option `-S'.

     Using this option, the program does not try very hard to remove
     references from contexts in output, but it succeeds in doing so
     _when_ the context ends exactly at the newline.  If option `-r' is
     used with `-S' default value, or when GNU extensions are disabled,
     this condition is always met and references are completely
     excluded from the output contexts.

`-S REGEXP'
`--sentence-regexp=REGEXP'
     This option selects which regular expression will describe the end
     of a line or the end of a sentence.  In fact, this regular
     expression is not the only distinction between end of lines or end
     of sentences, and input line boundaries have no special
     significance outside this option.  By default, when GNU extensions
     are enabled and if `-r' option is not used, end of sentences are
     used.  In this case, this REGEX is imported from GNU Emacs:

          [.?!][]\"')}]*\\($\\|\t\\|  \\)[ \t\n]*

     Whenever GNU extensions are disabled or if `-r' option is used, end
     of lines are used; in this case, the default REGEXP is just:

          \n

     Using an empty REGEXP is equivalent to completely disabling end of
     line or end of sentence recognition.  In this case, the whole file
     is considered to be a single big line or sentence.  The user might
     want to disallow all truncation flag generation as well, through
     option `-F ""'.  *Note Syntax of Regular Expressions:
     (emacs)Regexps.

     When the keywords happen to be near the beginning of the input
     line or sentence, this often creates an unused area at the
     beginning of the output context line; when the keywords happen to
     be near the end of the input line or sentence, this often creates
     an unused area at the end of the output context line.  The program
     tries to fill those unused areas by wrapping around context in
     them; the tail of the input line or sentence is used to fill the
     unused area on the left of the output line; the head of the input
     line or sentence is used to fill the unused area on the right of
     the output line.

     As a matter of convenience to the user, many usual backslashed
     escape sequences from the C language are recognized and converted
     to the corresponding characters by `ptx' itself.

`-W REGEXP'
`--word-regexp=REGEXP'
     This option selects which regular expression will describe each
     keyword.  By default, if GNU extensions are enabled, a word is a
     sequence of letters; the REGEXP used is `\w+'.  When GNU
     extensions are disabled, a word is by default anything which ends
     with a space, a tab or a newline; the REGEXP used is `[^ \t\n]+'.

     An empty REGEXP is equivalent to not using this option.  *Note
     Syntax of Regular Expressions: (emacs)Regexps.

     As a matter of convenience to the user, many usual backslashed
     escape sequences, as found in the C language, are recognized and
     converted to the corresponding characters by `ptx' itself.



File: coreutils.info,  Node: Output formatting in ptx,  Next: Compatibility in ptx,  Prev: Input processing in ptx,  Up: ptx invocation

7.7.4 Output formatting
-----------------------

Output format is mainly controlled by the `-O' and `-T' options
described in the table below.  When neither `-O' nor `-T' are selected,
and if GNU extensions are enabled, the program chooses an output format
suitable for a dumb terminal.  Each keyword occurrence is output to the
center of one line, surrounded by its left and right contexts.  Each
field is properly justified, so the concordance output can be readily
observed.  As a special feature, if automatic references are selected
by option `-A' and are output before the left context, that is, if
option `-R' is _not_ selected, then a colon is added after the
reference; this nicely interfaces with GNU Emacs `next-error'
processing.  In this default output format, each white space character,
like newline and tab, is merely changed to exactly one space, with no
special attempt to compress consecutive spaces.  This might change in
the future.  Except for those white space characters, every other
character of the underlying set of 256 characters is transmitted
verbatim.

   Output format is further controlled by the following options.

`-g NUMBER'
`--gap-size=NUMBER'
     Select the size of the minimum white space gap between the fields
     on the output line.

`-w NUMBER'
`--width=NUMBER'
     Select the maximum output width of each final line.  If references
     are used, they are included or excluded from the maximum output
     width depending on the value of option `-R'.  If this option is not
     selected, that is, when references are output before the left
     context, the maximum output width takes into account the maximum
     length of all references.  If this option is selected, that is,
     when references are output after the right context, the maximum
     output width does not take into account the space taken by
     references, nor the gap that precedes them.

`-A'
`--auto-reference'
     Select automatic references.  Each input line will have an
     automatic reference made up of the file name and the line ordinal,
     with a single colon between them.  However, the file name will be
     empty when standard input is being read.  If both `-A' and `-r'
     are selected, then the input reference is still read and skipped,
     but the automatic reference is used at output time, overriding the
     input reference.

`-R'
`--right-side-refs'
     In the default output format, when option `-R' is not used, any
     references produced by the effect of options `-r' or `-A' are
     placed to the far right of output lines, after the right context.
     With default output format, when the `-R' option is specified,
     references are rather placed at the beginning of each output line,
     before the left context.  For any other output format, option `-R'
     is ignored, with one exception:  with `-R' the width of references
     is _not_ taken into account in total output width given by `-w'.

     This option is automatically selected whenever GNU extensions are
     disabled.

`-F STRING'
`--flac-truncation=STRING'
     This option will request that any truncation in the output be
     reported using the string STRING.  Most output fields
     theoretically extend towards the beginning or the end of the
     current line, or current sentence, as selected with option `-S'.
     But there is a maximum allowed output line width, changeable
     through option `-w', which is further divided into space for
     various output fields.  When a field has to be truncated because
     it cannot extend beyond the beginning or the end of the current
     line to fit in, then a truncation occurs.  By default, the string
     used is a single slash, as in `-F /'.

     STRING may have more than one character, as in `-F ...'.  Also, in
     the particular case when STRING is empty (`-F ""'), truncation
     flagging is disabled, and no truncation marks are appended in this
     case.

     As a matter of convenience to the user, many usual backslashed
     escape sequences, as found in the C language, are recognized and
     converted to the corresponding characters by `ptx' itself.

`-M STRING'
`--macro-name=STRING'
     Select another STRING to be used instead of `xx', while generating
     output suitable for `nroff', `troff' or TeX.

`-O'
`--format=roff'
     Choose an output format suitable for `nroff' or `troff'
     processing.  Each output line will look like:

          .xx "TAIL" "BEFORE" "KEYWORD_AND_AFTER" "HEAD" "REF"

     so it will be possible to write a `.xx' roff macro to take care of
     the output typesetting.  This is the default output format when GNU
     extensions are disabled.  Option `-M' can be used to change `xx'
     to another macro name.

     In this output format, each non-graphical character, like newline
     and tab, is merely changed to exactly one space, with no special
     attempt to compress consecutive spaces.  Each quote character: `"'
     is doubled so it will be correctly processed by `nroff' or `troff'.

`-T'
`--format=tex'
     Choose an output format suitable for TeX processing.  Each output
     line will look like:

          \xx {TAIL}{BEFORE}{KEYWORD}{AFTER}{HEAD}{REF}

     so it will be possible to write a `\xx' definition to take care of
     the output typesetting.  Note that when references are not being
     produced, that is, neither option `-A' nor option `-r' is
     selected, the last parameter of each `\xx' call is inhibited.
     Option `-M' can be used to change `xx' to another macro name.

     In this output format, some special characters, like `$', `%',
     `&', `#' and `_' are automatically protected with a backslash.
     Curly brackets `{', `}' are protected with a backslash and a pair
     of dollar signs (to force mathematical mode).  The backslash
     itself produces the sequence `\backslash{}'.  Circumflex and tilde
     diacritical marks produce the sequence `^\{ }' and `~\{ }'
     respectively.  Other diacriticized characters of the underlying
     character set produce an appropriate TeX sequence as far as
     possible.  The other non-graphical characters, like newline and
     tab, and all other characters which are not part of ASCII, are
     merely changed to exactly one space, with no special attempt to
     compress consecutive spaces.  Let me know how to improve this
     special character processing for TeX.



File: coreutils.info,  Node: Compatibility in ptx,  Prev: Output formatting in ptx,  Up: ptx invocation

7.7.5 The GNU extensions to `ptx'
---------------------------------

This version of `ptx' contains a few features which do not exist in
System V `ptx'.  These extra features are suppressed by using the `-G'
command line option, unless overridden by other command line options.
Some GNU extensions cannot be recovered by overriding, so the simple
rule is to avoid `-G' if you care about GNU extensions.  Here are the
differences between this program and System V `ptx'.

   * This program can read many input files at once, it always writes
     the resulting concordance on standard output.  On the other hand,
     System V `ptx' reads only one file and sends the result to
     standard output or, if a second FILE parameter is given on the
     command, to that FILE.

     Having output parameters not introduced by options is a dangerous
     practice which GNU avoids as far as possible.  So, for using `ptx'
     portably between GNU and System V, you should always use it with a
     single input file, and always expect the result on standard
     output.  You might also want to automatically configure in a `-G'
     option to `ptx' calls in products using `ptx', if the configurator
     finds that the installed `ptx' accepts `-G'.

   * The only options available in System V `ptx' are options `-b',
     `-f', `-g', `-i', `-o', `-r', `-t' and `-w'.  All other options
     are GNU extensions and are not repeated in this enumeration.
     Moreover, some options have a slightly different meaning when GNU
     extensions are enabled, as explained below.

   * By default, concordance output is not formatted for `troff' or
     `nroff'.  It is rather formatted for a dumb terminal.  `troff' or
     `nroff' output may still be selected through option `-O'.

   * Unless `-R' option is used, the maximum reference width is
     subtracted from the total output line width.  With GNU extensions
     disabled, width of references is not taken into account in the
     output line width computations.

   * All 256 bytes, even null bytes, are always read and processed from
     input file with no adverse effect, even if GNU extensions are
     disabled.  However, System V `ptx' does not accept 8-bit
     characters, a few control characters are rejected, and the tilde
     `~' is also rejected.

   * Input line length is only limited by available memory, even if GNU
     extensions are disabled.  However, System V `ptx' processes only
     the first 200 characters in each line.

   * The break (non-word) characters default to be every character
     except all letters of the underlying character set, diacriticized
     or not.  When GNU extensions are disabled, the break characters
     default to space, tab and newline only.

   * The program makes better use of output line width.  If GNU
     extensions are disabled, the program rather tries to imitate
     System V `ptx', but still, there are some slight disposition
     glitches this program does not completely reproduce.

   * The user can specify both an Ignore file and an Only file.  This
     is not allowed with System V `ptx'.



File: coreutils.info,  Node: Operating on fields within a line,  Next: Operating on characters,  Prev: Operating on sorted files,  Up: Top

8 Operating on fields within a line
***********************************

* Menu:

* cut invocation::              Print selected parts of lines.
* paste invocation::            Merge lines of files.
* join invocation::             Join lines on a common field.


File: coreutils.info,  Node: cut invocation,  Next: paste invocation,  Up: Operating on fields within a line

8.1 `cut': Print selected parts of lines
========================================

`cut' writes to standard output selected parts of each line of each
input file, or standard input if no files are given or for a file name
of `-'.  Synopsis:

     cut [OPTION]... [FILE]...

   In the table which follows, the BYTE-LIST, CHARACTER-LIST, and
FIELD-LIST are one or more numbers or ranges (two numbers separated by
a dash) separated by commas.  Bytes, characters, and fields are
numbered starting at 1.  Incomplete ranges may be given: `-M' means
`1-M'; `N-' means `N' through end of line or last field.  The list
elements can be repeated, can overlap, and can be specified in any
order; but the selected input is written in the same order that it is
read, and is written exactly once.

   The program accepts the following options.  Also see *Note Common
options::.

`-b BYTE-LIST'
`--bytes=BYTE-LIST'
     Select for printing only the bytes in positions listed in
     BYTE-LIST.  Tabs and backspaces are treated like any other
     character; they take up 1 byte.  If an output delimiter is
     specified, (see the description of `--output-delimiter'), then
     output that string between ranges of selected bytes.

`-c CHARACTER-LIST'
`--characters=CHARACTER-LIST'
     Select for printing only the characters in positions listed in
     CHARACTER-LIST.  The same as `-b' for now, but
     internationalization will change that.  Tabs and backspaces are
     treated like any other character; they take up 1 character.  If an
     output delimiter is specified, (see the description of
     `--output-delimiter'), then output that string between ranges of
     selected bytes.

`-f FIELD-LIST'
`--fields=FIELD-LIST'
     Select for printing only the fields listed in FIELD-LIST.  Fields
     are separated by a TAB character by default.  Also print any line
     that contains no delimiter character, unless the
     `--only-delimited' (`-s') option is specified

`-d INPUT_DELIM_BYTE'
`--delimiter=INPUT_DELIM_BYTE'
     With `-f', use the first byte of INPUT_DELIM_BYTE as the input
     fields separator (default is TAB).

`-n'
     Do not split multi-byte characters (no-op for now).

`-s'
`--only-delimited'
     For `-f', do not print lines that do not contain the field
     separator character.  Normally, any line without a field separator
     is printed verbatim.

`--output-delimiter=OUTPUT_DELIM_STRING'
     With `-f', output fields are separated by OUTPUT_DELIM_STRING.
     The default with `-f' is to use the input delimiter.  When using
     `-b' or `-c' to select ranges of byte or character offsets (as
     opposed to ranges of fields), output OUTPUT_DELIM_STRING between
     non-overlapping ranges of selected bytes.

`--complement'
     This option is a GNU extension.  Select for printing the
     complement of the bytes, characters or fields selected with the
     `-b', `-c' or `-f' options.  In other words, do _not_ print the
     bytes, characters or fields specified via those options.  This
     option is useful when you have many fields and want to print all
     but a few of them.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: paste invocation,  Next: join invocation,  Prev: cut invocation,  Up: Operating on fields within a line

8.2 `paste': Merge lines of files
=================================

`paste' writes to standard output lines consisting of sequentially
corresponding lines of each given file, separated by a TAB character.
Standard input is used for a file name of `-' or if no input files are
given.

   For example:

     $ cat num2
     1
     2
     $ cat let3
     a
     b
     c
     $ paste num2 let3
     1       a
     2       b
             c

   Synopsis:

     paste [OPTION]... [FILE]...

   The program accepts the following options.  Also see *Note Common
options::.

`-s'
`--serial'
     Paste the lines of one file at a time rather than one line from
     each file.  Using the above example data:

          $ paste -s num2 let3
          1       2
          a       b       c

`-d DELIM-LIST'
`--delimiters=DELIM-LIST'
     Consecutively use the characters in DELIM-LIST instead of TAB to
     separate merged lines.  When DELIM-LIST is exhausted, start again
     at its beginning.  Using the above example data:

          $ paste -d '%_' num2 let3 num2
          1%a_1
          2%b_2
          %c_


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: join invocation,  Prev: paste invocation,  Up: Operating on fields within a line

8.3 `join': Join lines on a common field
========================================

`join' writes to standard output a line for each pair of input lines
that have identical join fields.  Synopsis:

     join [OPTION]... FILE1 FILE2

   Either FILE1 or FILE2 (but not both) can be `-', meaning standard
input.  FILE1 and FILE2 should be sorted on the join fields.

   Normally, the sort order is that of the collating sequence specified
by the `LC_COLLATE' locale.  Unless the `-t' option is given, the sort
comparison ignores blanks at the start of the join field, as in `sort
-b'.  If the `--ignore-case' option is given, the sort comparison
ignores the case of characters in the join field, as in `sort -f'.

   The `sort' and `join' commands should use consistent locales and
options if the output of `sort' is fed to `join'.  You can use a
command like `sort -k 1b,1' to sort a file on its default join field,
but if you select a non-default locale, join field, separator, or
comparison options, then you should do so consistently between `join'
and `sort'.

   As a GNU extension, if the input has no unpairable lines the sort
order can be any order that considers two fields to be equal if and
only if the sort comparison described above considers them to be equal.
For example:

     $ cat file1
     a a1
     c c1
     b b1
     $ cat file2
     a a2
     c c2
     b b2
     $ join file1 file2
     a a1 a2
     c c1 c2
     b b1 b2

   The defaults are:
   * the join field is the first field in each line;

   * fields in the input are separated by one or more blanks, with
     leading       blanks on the line ignored;

   * fields in the output are separated by a space;

   * each output line consists of the join field, the remaining fields
     from FILE1, then the remaining fields from FILE2.

   The program accepts the following options.  Also see *Note Common
options::.

`-a FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), in addition to the normal output.

`-e STRING'
     Replace those output fields that are missing in the input with
     STRING.

`-i'
`--ignore-case'
     Ignore differences in case when comparing keys.  With this option,
     the lines of the input files must be ordered in the same way.  Use
     `sort -f' to produce this ordering.

`-1 FIELD'
     Join on field FIELD (a positive integer) of file 1.

`-2 FIELD'
     Join on field FIELD (a positive integer) of file 2.

`-j FIELD'
     Equivalent to `-1 FIELD -2 FIELD'.

`-o FIELD-LIST'
     Construct each output line according to the format in FIELD-LIST.
     Each element in FIELD-LIST is either the single character `0' or
     has the form M.N where the file number, M, is `1' or `2' and N is
     a positive field number.

     A field specification of `0' denotes the join field.  In most
     cases, the functionality of the `0' field spec may be reproduced
     using the explicit M.N that corresponds to the join field.
     However, when printing unpairable lines (using either of the `-a'
     or `-v' options), there is no way to specify the join field using
     M.N in FIELD-LIST if there are unpairable lines in both files.  To
     give `join' that functionality, POSIX invented the `0' field
     specification notation.

     The elements in FIELD-LIST are separated by commas or blanks.
     Blank separators typically need to be quoted for the shell.  For
     example, the commands `join -o 1.2,2.2' and `join -o '1.2 2.2''
     are equivalent.

     All output lines--including those printed because of any -a or -v
     option--are subject to the specified FIELD-LIST.

`-t CHAR'
     Use character CHAR as the input and output field separator.  Treat
     as significant each occurrence of CHAR in the input file.  Use
     `sort -t CHAR', without the `-b' option of `sort', to produce this
     ordering.

`-v FILE-NUMBER'
     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), instead of the normal output.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Operating on characters,  Next: Directory listing,  Prev: Operating on fields within a line,  Up: Top

9 Operating on characters
*************************

This commands operate on individual characters.

* Menu:

* tr invocation::               Translate, squeeze, and/or delete characters.
* expand invocation::           Convert tabs to spaces.
* unexpand invocation::         Convert spaces to tabs.


File: coreutils.info,  Node: tr invocation,  Next: expand invocation,  Up: Operating on characters

9.1 `tr': Translate, squeeze, and/or delete characters
======================================================

Synopsis:

     tr [OPTION]... SET1 [SET2]

   `tr' copies standard input to standard output, performing one of the
following operations:

   * translate, and optionally squeeze repeated characters in the
     result,

   * squeeze repeated characters,

   * delete characters,

   * delete characters, then squeeze repeated characters from the
     result.

   The SET1 and (if given) SET2 arguments define ordered sets of
characters, referred to below as SET1 and SET2.  These sets are the
characters of the input that `tr' operates on.  The `--complement'
(`-c', `-C') option replaces SET1 with its complement (all of the
characters that are not in SET1).

   Currently `tr' fully supports only single-byte characters.
Eventually it will support multibyte characters; when it does, the `-C'
option will cause it to complement the set of characters, whereas `-c'
will cause it to complement the set of values.  This distinction will
matter only when some values are not characters, and this is possible
only in locales using multibyte encodings when the input contains
encoding errors.

   The program accepts the `--help' and `--version' options.  *Note
Common options::.  Options must precede operands.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Character sets::              Specifying sets of characters.
* Translating::                 Changing one set of characters to another.
* Squeezing::                   Squeezing repeats and deleting.


File: coreutils.info,  Node: Character sets,  Next: Translating,  Up: tr invocation

9.1.1 Specifying sets of characters
-----------------------------------

The format of the SET1 and SET2 arguments resembles the format of
regular expressions; however, they are not regular expressions, only
lists of characters.  Most characters simply represent themselves in
these strings, but the strings can contain the shorthands listed below,
for convenience.  Some of them can be used only in SET1 or SET2, as
noted below.

Backslash escapes
     The following backslash escape sequences are recognized:

    `\a'
          Control-G.

    `\b'
          Control-H.

    `\f'
          Control-L.

    `\n'
          Control-J.

    `\r'
          Control-M.

    `\t'
          Control-I.

    `\v'
          Control-K.

    `\OOO'
          The character with the value given by OOO, which is 1 to 3
          octal digits,

    `\\'
          A backslash.

     While a backslash followed by a character not listed above is
     interpreted as that character, the backslash also effectively
     removes any special significance, so it is useful to escape `[',
     `]', `*', and `-'.

Ranges
     The notation `M-N' expands to all of the characters from M through
     N, in ascending order.  M should collate before N; if it doesn't,
     an error results.  As an example, `0-9' is the same as
     `0123456789'.

     GNU `tr' does not support the System V syntax that uses square
     brackets to enclose ranges.  Translations specified in that format
     sometimes work as expected, since the brackets are often
     transliterated to themselves.  However, they should be avoided
     because they sometimes behave unexpectedly.  For example, `tr -d
     '[0-9]'' deletes brackets as well as digits.

     Many historically common and even accepted uses of ranges are not
     portable.  For example, on EBCDIC hosts using the `A-Z' range will
     not do what most would expect because `A' through `Z' are not
     contiguous as they are in ASCII.  If you can rely on a POSIX
     compliant version of `tr', then the best way to work around this
     is to use character classes (see below).  Otherwise, it is most
     portable (and most ugly) to enumerate the members of the ranges.

Repeated characters
     The notation `[C*N]' in SET2 expands to N copies of character C.
     Thus, `[y*6]' is the same as `yyyyyy'.  The notation `[C*]' in
     STRING2 expands to as many copies of C as are needed to make SET2
     as long as SET1.  If N begins with `0', it is interpreted in
     octal, otherwise in decimal.

Character classes
     The notation `[:CLASS:]' expands to all of the characters in the
     (predefined) class CLASS.  The characters expand in no particular
     order, except for the `upper' and `lower' classes, which expand in
     ascending order.  When the `--delete' (`-d') and
     `--squeeze-repeats' (`-s') options are both given, any character
     class can be used in SET2.  Otherwise, only the character classes
     `lower' and `upper' are accepted in SET2, and then only if the
     corresponding character class (`upper' and `lower', respectively)
     is specified in the same relative position in SET1.  Doing this
     specifies case conversion.  The class names are given below; an
     error results when an invalid class name is given.

    `alnum'
          Letters and digits.

    `alpha'
          Letters.

    `blank'
          Horizontal whitespace.

    `cntrl'
          Control characters.

    `digit'
          Digits.

    `graph'
          Printable characters, not including space.

    `lower'
          Lowercase letters.

    `print'
          Printable characters, including space.

    `punct'
          Punctuation characters.

    `space'
          Horizontal or vertical whitespace.

    `upper'
          Uppercase letters.

    `xdigit'
          Hexadecimal digits.

Equivalence classes
     The syntax `[=C=]' expands to all of the characters that are
     equivalent to C, in no particular order.  Equivalence classes are
     a relatively recent invention intended to support non-English
     alphabets.  But there seems to be no standard way to define them
     or determine their contents.  Therefore, they are not fully
     implemented in GNU `tr'; each character's equivalence class
     consists only of that character, which is of no particular use.



File: coreutils.info,  Node: Translating,  Next: Squeezing,  Prev: Character sets,  Up: tr invocation

9.1.2 Translating
-----------------

`tr' performs translation when SET1 and SET2 are both given and the
`--delete' (`-d') option is not given.  `tr' translates each character
of its input that is in SET1 to the corresponding character in SET2.
Characters not in SET1 are passed through unchanged.  When a character
appears more than once in SET1 and the corresponding characters in SET2
are not all the same, only the final one is used.  For example, these
two commands are equivalent:

     tr aaa xyz
     tr a z

   A common use of `tr' is to convert lowercase characters to
uppercase.  This can be done in many ways.  Here are three of them:

     tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
     tr a-z A-Z
     tr '[:lower:]' '[:upper:]'

But note that using ranges like `a-z' above is not portable.

   When `tr' is performing translation, SET1 and SET2 typically have
the same length.  If SET1 is shorter than SET2, the extra characters at
the end of SET2 are ignored.

   On the other hand, making SET1 longer than SET2 is not portable;
POSIX says that the result is undefined.  In this situation, BSD `tr'
pads SET2 to the length of SET1 by repeating the last character of SET2
as many times as necessary.  System V `tr' truncates SET1 to the length
of SET2.

   By default, GNU `tr' handles this case like BSD `tr'.  When the
`--truncate-set1' (`-t') option is given, GNU `tr' handles this case
like the System V `tr' instead.  This option is ignored for operations
other than translation.

   Acting like System V `tr' in this case breaks the relatively common
BSD idiom:

     tr -cs A-Za-z0-9 '\012'

because it converts only zero bytes (the first element in the
complement of SET1), rather than all non-alphanumerics, to newlines.

By the way, the above idiom is not portable because it uses ranges, and
it assumes that the octal code for newline is 012.  Assuming a POSIX
compliant `tr', here is a better way to write it:

     tr -cs '[:alnum:]' '[\n*]'


File: coreutils.info,  Node: Squeezing,  Prev: Translating,  Up: tr invocation

9.1.3 Squeezing repeats and deleting
------------------------------------

When given just the `--delete' (`-d') option, `tr' removes any input
characters that are in SET1.

   When given just the `--squeeze-repeats' (`-s') option, `tr' replaces
each input sequence of a repeated character that is in SET1 with a
single occurrence of that character.

   When given both `--delete' and `--squeeze-repeats', `tr' first
performs any deletions using SET1, then squeezes repeats from any
remaining characters using SET2.

   The `--squeeze-repeats' option may also be used when translating, in
which case `tr' first performs translation, then squeezes repeats from
any remaining characters using SET2.

   Here are some examples to illustrate various combinations of options:

   * Remove all zero bytes:

          tr -d '\0'

   * Put all words on lines by themselves.  This converts all
     non-alphanumeric characters to newlines, then squeezes each string
     of repeated newlines into a single newline:

          tr -cs '[:alnum:]' '[\n*]'

   * Convert each sequence of repeated newlines to a single newline:

          tr -s '\n'

   * Find doubled occurrences of words in a document.  For example,
     people often write "the the" with the repeated words separated by
     a newline.  The Bourne shell script below works first by
     converting each sequence of punctuation and blank characters to a
     single newline.  That puts each "word" on a line by itself.  Next
     it maps all uppercase characters to lower case, and finally it
     runs `uniq' with the `-d' option to print out only the words that
     were repeated.

          #!/bin/sh
          cat -- "$@" \
            | tr -s '[:punct:][:blank:]' '[\n*]' \
            | tr '[:upper:]' '[:lower:]' \
            | uniq -d

   * Deleting a small set of characters is usually straightforward.
     For example, to remove all `a's, `x's, and `M's you would do this:

          tr -d axM

     However, when `-' is one of those characters, it can be tricky
     because `-' has special meanings.  Performing the same task as
     above but also removing all `-' characters, we might try `tr -d
     -axM', but that would fail because `tr' would try to interpret
     `-a' as a command-line option.  Alternatively, we could try
     putting the hyphen inside the string, `tr -d a-xM', but that
     wouldn't work either because it would make `tr' interpret `a-x' as
     the range of characters `a'...`x' rather than the three.  One way
     to solve the problem is to put the hyphen at the end of the list
     of characters:

          tr -d axM-

     Or you can use `--' to terminate option processing:

          tr -d -- -axM

     More generally, use the character class notation `[=c=]' with `-'
     (or any other character) in place of the `c':

          tr -d '[=-=]axM'

     Note how single quotes are used in the above example to protect the
     square brackets from interpretation by a shell.



File: coreutils.info,  Node: expand invocation,  Next: unexpand invocation,  Prev: tr invocation,  Up: Operating on characters

9.2 `expand': Convert tabs to spaces
====================================

`expand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of `-', to standard output, with tab
characters converted to the appropriate number of spaces.  Synopsis:

     expand [OPTION]... [FILE]...

   By default, `expand' converts all tabs to spaces.  It preserves
backspace characters in the output; they decrement the column count for
tab calculations.  The default action is equivalent to `-t 8' (set tabs
every 8 columns).

   The program accepts the following options.  Also see *Note Common
options::.

`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 spaces apart
     (default is 8).  Otherwise, set the tabs at columns TAB1, TAB2,
     ... (numbered from 0), and replace any tabs beyond the last tab
     stop given with single spaces.  Tab stops can be separated by
     blanks as well as by commas.

     For compatibility, GNU `expand' also accepts the obsolete option
     syntax, `-T1[,T2]...'.  New scripts should use `-t T1[,T2]...'
     instead.

`-i'
`--initial'
     Only convert initial tabs (those that precede all non-space or
     non-tab characters) on each line to spaces.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: unexpand invocation,  Prev: expand invocation,  Up: Operating on characters

9.3 `unexpand': Convert spaces to tabs
======================================

`unexpand' writes the contents of each given FILE, or standard input if
none are given or for a FILE of `-', to standard output, converting
blanks at the beginning of each line into as many tab characters as
needed.  In the default POSIX locale, a "blank" is a space or a tab;
other locales may specify additional blank characters.  Synopsis:

     unexpand [OPTION]... [FILE]...

   By default, `unexpand' converts only initial blanks (those that
precede all non-blank characters) on each line.  It preserves backspace
characters in the output; they decrement the column count for tab
calculations.  By default, tabs are set at every 8th column.

   The program accepts the following options.  Also see *Note Common
options::.

`-t TAB1[,TAB2]...'
`--tabs=TAB1[,TAB2]...'
     If only one tab stop is given, set the tabs TAB1 columns apart
     instead of the default 8.  Otherwise, set the tabs at columns
     TAB1, TAB2, ... (numbered from 0), and leave blanks beyond the tab
     stops given unchanged.  Tab stops can be separated by blanks as
     well as by commas.  This option implies the `-a' option.

     For compatibility, GNU `unexpand' supports the obsolete option
     syntax, `-TAB1[,TAB2]...', where tab stops must be separated by
     commas.  (Unlike `-t', this obsolete option does not imply `-a'.)
     New scripts should use `--first-only -t TAB1[,TAB2]...' instead.

`-a'
`--all'
     Also convert all sequences of two or more blanks just before a tab
     stop, even if they occur after non-blank characters in a line.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Directory listing,  Next: Basic operations,  Prev: Operating on characters,  Up: Top

10 Directory listing
********************

This chapter describes the `ls' command and its variants `dir' and
`vdir', which list information about files.

* Menu:

* ls invocation::               List directory contents.
* dir invocation::              Briefly ls.
* vdir invocation::             Verbosely ls.
* dircolors invocation::        Color setup for ls, etc.


File: coreutils.info,  Node: ls invocation,  Next: dir invocation,  Up: Directory listing

10.1 `ls': List directory contents
==================================

The `ls' program lists information about files (of any type, including
directories).  Options and file arguments can be intermixed
arbitrarily, as usual.

   For non-option command-line arguments that are directories, by
default `ls' lists the contents of directories, not recursively, and
omitting files with names beginning with `.'.  For other non-option
arguments, by default `ls' lists just the file name.  If no non-option
argument is specified, `ls' operates on the current directory, acting
as if it had been invoked with a single argument of `.'.

   By default, the output is sorted alphabetically, according to the
locale settings in effect.(1) If standard output is a terminal, the
output is in columns (sorted vertically) and control characters are
output as question marks; otherwise, the output is listed one per line
and control characters are output as-is.

   Because `ls' is such a fundamental program, it has accumulated many
options over the years.  They are described in the subsections below;
within each section, options are listed alphabetically (ignoring case).
The division of options into the subsections is not absolute, since some
options affect more than one aspect of `ls''s operation.

   Exit status:

     0 success
     1 minor problems (e.g., a subdirectory was not found)
     2 serious trouble (e.g., memory exhausted)

   Also see *Note Common options::.

* Menu:

* Which files are listed::
* What information is listed::
* Sorting the output::
* More details about version sort::
* General output formatting::
* Formatting file timestamps::
* Formatting the file names::

   ---------- Footnotes ----------

   (1) If you use a non-POSIX locale (e.g., by setting `LC_ALL' to
`en_US'), then `ls' may produce output that is sorted differently than
you're accustomed to.  In that case, set the `LC_ALL' environment
variable to `C'.


File: coreutils.info,  Node: Which files are listed,  Next: What information is listed,  Up: ls invocation

10.1.1 Which files are listed
-----------------------------

These options determine which files `ls' lists information for.  By
default, `ls' lists files and the contents of any directories on the
command line, except that in directories it ignores files whose names
start with `.'.

`-a'
`--all'
     In directories, do not ignore file names that start with `.'.

`-A'
`--almost-all'
     In directories, do not ignore all file names that start with `.';
     ignore only `.' and `..'.  The `--all' (`-a') option overrides
     this option.

`-B'
`--ignore-backups'
     In directories, ignore files that end with `~'.  This option is
     equivalent to `--ignore='*~' --ignore='.*~''.

`-d'
`--directory'
     List just the names of directories, as with other types of files,
     rather than listing their contents.  Do not follow symbolic links
     listed on the command line unless the `--dereference-command-line'
     (`-H'), `--dereference' (`-L'), or
     `--dereference-command-line-symlink-to-dir' options are specified.

`-H'
`--dereference-command-line'
     If a command line argument specifies a symbolic link, show
     information for the file the link references rather than for the
     link itself.

`--dereference-command-line-symlink-to-dir'
     Do not dereference symbolic links, with one exception: if a
     command line argument specifies a symbolic link that refers to a
     directory, show information for that directory rather than for the
     link itself.  This is the default behavior when no other
     dereferencing-related option has been specified (`--classify'
     (`-F'), `--directory' (`-d'), (`-l'), `--dereference' (`-L'), or
     `--dereference-command-line' (`-H')).

`--group-directories-first'
     Group all the directories before the files and then sort the
     directories and the files separately using the selected sort key
     (see -sort option).  That is, this option specifies a primary sort
     key, and the -sort option specifies a secondary key.

`--hide=PATTERN'
     In directories, ignore files whose names match the shell pattern
     PATTERN, unless the `--all' (`-a') or `--almost-all' (`-A') is
     also given.  This option acts like `--ignore=PATTERN' except that
     it has no effect if `--all' (`-a') or `--almost-all' (`-A') is
     also given.

     This option can be useful in shell aliases.  For example, if `lx'
     is an alias for `ls --hide='*~'' and `ly' is an alias for `ls
     --ignore='*~'', then the command `lx -A' lists the file `README~'
     even though `ly -A' would not.

`-I PATTERN'
`--ignore=PATTERN'
     In directories, ignore files whose names match the shell pattern
     (not regular expression) PATTERN.  As in the shell, an initial `.'
     in a file name does not match a wildcard at the start of PATTERN.
     Sometimes it is useful to give this option several times.  For
     example,

          $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'

     The first option ignores names of length 3 or more that start with
     `.', the second ignores all two-character names that start with `.'
     except `..', and the third ignores names that start with `#'.

`-L'
`--dereference'
     When showing file information for a symbolic link, show information
     for the file the link references rather than the link itself.
     However, even with this option, `ls' still prints the name of the
     link itself, not the name of the file that the link points to.

`-R'
`--recursive'
     List the contents of all directories recursively.



File: coreutils.info,  Node: What information is listed,  Next: Sorting the output,  Prev: Which files are listed,  Up: ls invocation

10.1.2 What information is listed
---------------------------------

These options affect the information that `ls' displays.  By default,
only file names are shown.

`--author'
     List each file's author when producing long format directory
     listings.  In GNU/Hurd, file authors can differ from their owners,
     but in other operating systems the two are the same.

`-D'
`--dired'
     With the long listing (`-l') format, print an additional line after
     the main output:

          //DIRED// BEG1 END1 BEG2 END2 ...

     The BEGN and ENDN are unsigned integers that record the byte
     position of the beginning and end of each file name in the output.
     This makes it easy for Emacs to find the names, even when they
     contain unusual characters such as space or newline, without fancy
     searching.

     If directories are being listed recursively (`-R'), output a
     similar line with offsets for each subdirectory name:

          //SUBDIRED// BEG1 END1 ...

     Finally, output a line of the form:

          //DIRED-OPTIONS// --quoting-style=WORD

     where WORD is the quoting style (*note Formatting the file
     names::).

     Here is an actual example:

          $ mkdir -p a/sub/deeper a/sub2
          $ touch a/f1 a/f2
          $ touch a/sub/deeper/file
          $ ls -gloRF --dired a
            a:
            total 8
            -rw-r--r-- 1    0 Jun 10 12:27 f1
            -rw-r--r-- 1    0 Jun 10 12:27 f2
            drwxr-xr-x 3 4096 Jun 10 12:27 sub/
            drwxr-xr-x 2 4096 Jun 10 12:27 sub2/

            a/sub:
            total 4
            drwxr-xr-x 2 4096 Jun 10 12:27 deeper/

            a/sub/deeper:
            total 0
            -rw-r--r-- 1 0 Jun 10 12:27 file

            a/sub2:
            total 0
          //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
          //SUBDIRED// 2 3 167 172 228 240 290 296
          //DIRED-OPTIONS// --quoting-style=literal

     Note that the pairs of offsets on the `//DIRED//' line above
     delimit these names: `f1', `f2', `sub', `sub2', `deeper', `file'.
     The offsets on the `//SUBDIRED//' line delimit the following
     directory names: `a', `a/sub', `a/sub/deeper', `a/sub2'.

     Here is an example of how to extract the fifth entry name,
     `deeper', corresponding to the pair of offsets, 222 and 228:

          $ ls -gloRF --dired a > out
          $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
          deeper

     Note that although the listing above includes a trailing slash for
     the `deeper' entry, the offsets select the name without the
     trailing slash.  However, if you invoke `ls' with `--dired' along
     with an option like `--escape' (aka `-b') and operate on a file
     whose name contains special characters, notice that the backslash
     _is_ included:

          $ touch 'a b'
          $ ls -blog --dired 'a b'
            -rw-r--r-- 1 0 Jun 10 12:28 a\ b
          //DIRED// 30 34
          //DIRED-OPTIONS// --quoting-style=escape

     If you use a quoting style that adds quote marks (e.g.,
     `--quoting-style=c'), then the offsets include the quote marks.
     So beware that the user may select the quoting style via the
     environment variable `QUOTING_STYLE'.  Hence, applications using
     `--dired' should either specify an explicit
     `--quoting-style=literal' option (aka `-N' or `--literal') on the
     command line, or else be prepared to parse the escaped names.

`--full-time'
     Produce long format directory listings, and list times in full.
     It is equivalent to using `--format=long' with
     `--time-style=full-iso' (*note Formatting file timestamps::).

`-g'
     Produce long format directory listings, but don't display owner
     information.

`-G'
`--no-group'
     Inhibit display of group information in a long format directory
     listing.  (This is the default in some non-GNU versions of `ls',
     so we provide this option for compatibility.)

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     Use the `--si' option if you prefer powers of 1000.

`-i'
`--inode'
     Print the inode number (also called the file serial number and
     index number) of each file to the left of the file name.  (This
     number uniquely identifies each file within a particular file
     system.)

`-l'
`--format=long'
`--format=verbose'
     In addition to the name of each file, print the file type, file
     mode bits, number of hard links, owner name, group name, size, and
     timestamp (*note Formatting file timestamps::), normally the
     modification time.  Print question marks for information that
     cannot be determined.

     Normally the size is printed as a byte count without punctuation,
     but this can be overridden (*note Block size::).  For example, `-h'
     prints an abbreviated, human-readable count, and
     `--block-size="'1"' prints a byte count with the thousands
     separator of the current locale.

     For each directory that is listed, preface the files with a line
     `total BLOCKS', where BLOCKS is the total disk allocation for all
     files in that directory.  The block size currently defaults to 1024
     bytes, but this can be overridden (*note Block size::).  The
     BLOCKS computed counts each hard link separately; this is arguably
     a deficiency.

     The file type is one of the following characters:

    `-'
          regular file

    `b'
          block special file

    `c'
          character special file

    `C'
          high performance ("contiguous data") file

    `d'
          directory

    `D'
          door (Solaris 2.5 and up)

    `l'
          symbolic link

    `M'
          off-line ("migrated") file (Cray DMF)

    `n'
          network special file (HP-UX)

    `p'
          FIFO (named pipe)

    `P'
          port (Solaris 10 and up)

    `s'
          socket

    `?'
          some other file type

     The file mode bits listed are similar to symbolic mode
     specifications (*note Symbolic Modes::).  But `ls' combines
     multiple bits into the third character of each set of permissions
     as follows:

    `s'
          If the set-user-ID or set-group-ID bit and the corresponding
          executable bit are both set.

    `S'
          If the set-user-ID or set-group-ID bit is set but the
          corresponding executable bit is not set.

    `t'
          If the restricted deletion flag or sticky bit, and the
          other-executable bit, are both set.  The restricted deletion
          flag is another name for the sticky bit.  *Note Mode
          Structure::.

    `T'
          If the restricted deletion flag or sticky bit is set but the
          other-executable bit is not set.

    `x'
          If the executable bit is set and none of the above apply.

    `-'
          Otherwise.

     Following the file mode bits is a single character that specifies
     whether an alternate access method such as an access control list
     applies to the file.  When the character following the file mode
     bits is a space, there is no alternate access method.  When it is
     a printing character, then there is such a method.

     For a file with an extended access control list, a `+' character is
     listed.  Basic access control lists are equivalent to the
     permissions listed, and are not considered an alternate access
     method.

`-n'
`--numeric-uid-gid'
     Produce long format directory listings, but display numeric user
     and group IDs instead of the owner and group names.

`-o'
     Produce long format directory listings, but don't display group
     information.  It is equivalent to using `--format=long' with
     `--no-group' .

`-s'
`--size'
     Print the disk allocation of each file to the left of the file
     name.  This is the amount of disk space used by the file, which is
     usually a bit more than the file's size, but it can be less if the
     file has holes.

     Normally the disk allocation is printed in units of 1024 bytes,
     but this can be overridden (*note Block size::).

     For files that are NFS-mounted from an HP-UX system to a BSD
     system, this option reports sizes that are half the correct
     values.  On HP-UX systems, it reports sizes that are twice the
     correct values for files that are NFS-mounted from BSD systems.
     This is due to a flaw in HP-UX; it also affects the HP-UX `ls'
     program.

`--si'
     Append an SI-style abbreviation to each size, such as `M' for
     megabytes.  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  This option is equivalent to `--block-size=si'.
     Use the `-h' or `--human-readable' option if you prefer powers of
     1024.



File: coreutils.info,  Node: Sorting the output,  Next: More details about version sort,  Prev: What information is listed,  Up: ls invocation

10.1.3 Sorting the output
-------------------------

These options change the order in which `ls' sorts the information it
outputs.  By default, sorting is done by character code (e.g., ASCII
order).

`-c'
`--time=ctime'
`--time=status'
     If the long listing format (e.g., `-l', `-o') is being used, print
     the status change time (the `ctime' in the inode) instead of the
     modification time.  When explicitly sorting by time (`--sort=time'
     or `-t') or when not using a long listing format, sort according
     to the status change time.

`-f'
     Primarily, like `-U'--do not sort; list the files in whatever
     order they are stored in the directory.  But also enable `-a' (list
     all files) and disable `-l', `--color', and `-s' (if they were
     specified before the `-f').

`-r'
`--reverse'
     Reverse whatever the sorting method is--e.g., list files in reverse
     alphabetical order, youngest first, smallest first, or whatever.

`-S'
`--sort=size'
     Sort by file size, largest first.

`-t'
`--sort=time'
     Sort by modification time (the `mtime' in the inode), newest first.

`-u'
`--time=atime'
`--time=access'
`--time=use'
     If the long listing format (e.g., `--format=long') is being used,
     print the last access time (the `atime' in the inode).  When
     explicitly sorting by time (`--sort=time' or `-t') or when not
     using a long listing format, sort according to the access time.

`-U'
`--sort=none'
     Do not sort; list the files in whatever order they are stored in
     the directory.  (Do not do any of the other unrelated things that
     `-f' does.)  This is especially useful when listing very large
     directories, since not doing any sorting can be noticeably faster.

`-v'
`--sort=version'
     Sort by version name and number, lowest first.  It behaves like a
     default sort, except that each sequence of decimal digits is
     treated numerically as an index/version number.  (*Note More
     details about version sort::.)

`-X'
`--sort=extension'
     Sort directory contents alphabetically by file extension
     (characters after the last `.'); files with no extension are
     sorted first.



File: coreutils.info,  Node: More details about version sort,  Next: General output formatting,  Prev: Sorting the output,  Up: ls invocation

10.1.4 More details about version sort
--------------------------------------

The version sort takes into account the fact that file names frequently
include indices or version numbers.  Standard sorting functions usually
do not produce the ordering that people expect because comparisons are
made on a character-by-character basis.  The version sort addresses
this problem, and is especially useful when browsing directories that
contain many files with indices/version numbers in their names:

     $ ls -1            $ ls -1v
     foo.zml-1.gz       foo.zml-1.gz
     foo.zml-100.gz     foo.zml-2.gz
     foo.zml-12.gz      foo.zml-6.gz
     foo.zml-13.gz      foo.zml-12.gz
     foo.zml-2.gz       foo.zml-13.gz
     foo.zml-25.gz      foo.zml-25.gz
     foo.zml-6.gz       foo.zml-100.gz

   Note also that numeric parts with leading zeros are considered as
fractional one:

     $ ls -1            $ ls -1v
     abc-1.007.tgz      abc-1.007.tgz
     abc-1.012b.tgz     abc-1.01a.tgz
     abc-1.01a.tgz      abc-1.012b.tgz

   This functionality is implemented using the `strverscmp' function.
*Note String/Array Comparison: (libc)String/Array Comparison.  One
result of that implementation decision is that `ls -v' does not use the
locale category, `LC_COLLATE'.  As a result, non-numeric prefixes are
sorted as if `LC_COLLATE' were set to `C'.


File: coreutils.info,  Node: General output formatting,  Next: Formatting file timestamps,  Prev: More details about version sort,  Up: ls invocation

10.1.5 General output formatting
--------------------------------

These options affect the appearance of the overall output.

`-1'
`--format=single-column'
     List one file per line.  This is the default for `ls' when standard
     output is not a terminal.

`-C'
`--format=vertical'
     List files in columns, sorted vertically.  This is the default for
     `ls' if standard output is a terminal.  It is always the default
     for the `dir' program.  GNU `ls' uses variable width columns to
     display as many files as possible in the fewest lines.

`--color [=WHEN]'
     Specify whether to use color for distinguishing file types.  WHEN
     may be omitted, or one of:
        * none - Do not use color at all.  This is the default.

        * auto - Only use color if standard output is a terminal.

        * always - Always use color.
     Specifying `--color' and no WHEN is equivalent to `--color=always'.
     Piping a colorized listing through a pager like `more' or `less'
     usually produces unreadable results.  However, using `more -f'
     does seem to work.

`-F'
`--classify'
`--indicator-style=classify'
     Append a character to each file name indicating the file type.
     Also, for regular files that are executable, append `*'.  The file
     type indicators are `/' for directories, `@' for symbolic links,
     `|' for FIFOs, `=' for sockets, `>' for doors, and nothing for
     regular files.  Do not follow symbolic links listed on the command
     line unless the `--dereference-command-line' (`-H'),
     `--dereference' (`-L'), or
     `--dereference-command-line-symlink-to-dir' options are specified.

`--file-type'
`--indicator-style=file-type'
     Append a character to each file name indicating the file type.
     This is like `-F', except that executables are not marked.

`--indicator-style=WORD'
     Append a character indicator with style WORD to entry names, as
     follows:

    `none'
          Do not append any character indicator; this is the default.

    `slash'
          Append `/' for directories.  This is the same as the `-p'
          option.

    `file-type'
          Append `/' for directories, `@' for symbolic links, `|' for
          FIFOs, `=' for sockets, and nothing for regular files.  This
          is the same as the `--file-type' option.

    `classify'
          Append `*' for executable regular files, otherwise behave as
          for `file-type'.  This is the same as the `-F' or
          `--classify' option.

`-k'
     Print file sizes in 1024-byte blocks, overriding the default block
     size (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-m'
`--format=commas'
     List files horizontally, with as many as will fit on each line,
     separated by `, ' (a comma and a space).

`-p'
`--indicator-style=slash'
     Append a `/' to directory names.

`-x'
`--format=across'
`--format=horizontal'
     List the files in columns, sorted horizontally.

`-T COLS'
`--tabsize=COLS'
     Assume that each tab stop is COLS columns wide.  The default is 8.
     `ls' uses tabs where possible in the output, for efficiency.  If
     COLS is zero, do not use tabs at all.

     Some terminal emulators (at least Apple Terminal 1.5 (133) from
     Mac OS X 10.4.8) do not properly align columns to the right of a
     TAB following a non-ASCII byte.  If you use such a terminal
     emulator, use the `-T0' option or put `TABSIZE=0' in your
     environment to tell `ls' to align using spaces, not tabs.

`-w'
`--width=COLS'
     Assume the screen is COLS columns wide.  The default is taken from
     the terminal settings if possible; otherwise the environment
     variable `COLUMNS' is used if it is set; otherwise the default is
     80.



File: coreutils.info,  Node: Formatting file timestamps,  Next: Formatting the file names,  Prev: General output formatting,  Up: ls invocation

10.1.6 Formatting file timestamps
---------------------------------

By default, file timestamps are listed in abbreviated form.  Most
locales use a timestamp like `2002-03-30 23:45'.  However, the default
POSIX locale uses a date like `Mar 30  2002' for non-recent timestamps,
and a date-without-year and time like `Mar 30 23:45' for recent
timestamps.

   A timestamp is considered to be "recent" if it is less than six
months old, and is not dated in the future.  If a timestamp dated today
is not listed in recent form, the timestamp is in the future, which
means you probably have clock skew problems which may break programs
like `make' that rely on file timestamps.

   Time stamps are listed according to the time zone rules specified by
the `TZ' environment variable, or by the system default rules if `TZ'
is not set.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

   The following option changes how file timestamps are printed.

`--time-style=STYLE'
     List timestamps in style STYLE.  The STYLE should be one of the
     following:

    `+FORMAT'
          List timestamps using FORMAT, where FORMAT is interpreted
          like the format argument of `date' (*note date invocation::).
          For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `ls'
          to list timestamps like `2002-03-30 23:45:56'.  As with
          `date', FORMAT's interpretation is affected by the `LC_TIME'
          locale category.

          If FORMAT contains two format strings separated by a newline,
          the former is used for non-recent files and the latter for
          recent files; if you want output columns to line up, you may
          need to insert spaces in one of the two formats.

    `full-iso'
          List timestamps in full using ISO 8601 date, time, and time
          zone format with nanosecond precision, e.g., `2002-03-30
          23:45:56.477817180 -0700'.  This style is equivalent to
          `+%Y-%m-%d %H:%M:%S.%N %z'.

          This is useful because the time output includes all the
          information that is available from the operating system.  For
          example, this can help explain `make''s behavior, since GNU
          `make' uses the full timestamp to determine whether a file is
          out of date.

    `long-iso'
          List ISO 8601 date and time in minutes, e.g., `2002-03-30
          23:45'.  These timestamps are shorter than `full-iso'
          timestamps, and are usually good enough for everyday work.
          This style is equivalent to `+%Y-%m-%d %H:%M'.

    `iso'
          List ISO 8601 dates for non-recent timestamps (e.g.,
          `2002-03-30 '), and ISO 8601 month, day, hour, and minute for
          recent timestamps (e.g., `03-30 23:45').  These timestamps
          are uglier than `long-iso' timestamps, but they carry nearly
          the same information in a smaller space and their brevity
          helps `ls' output fit within traditional 80-column output
          lines.  The following two `ls' invocations are equivalent:

               newline='
               '
               ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
               ls -l --time-style="iso"

    `locale'
          List timestamps in a locale-dependent form.  For example, a
          Finnish locale might list non-recent timestamps like `maalis
          30  2002' and recent timestamps like `maalis 30 23:45'.
          Locale-dependent timestamps typically consume more space than
          `iso' timestamps and are harder for programs to parse because
          locale conventions vary so widely, but they are easier for
          many people to read.

          The `LC_TIME' locale category specifies the timestamp format.
          The default POSIX locale uses timestamps like `Mar 30  2002'
          and `Mar 30 23:45'; in this locale, the following two `ls'
          invocations are equivalent:

               newline='
               '
               ls -l --time-style="+%b %e  %Y$newline%b %e %H:%M"
               ls -l --time-style="locale"

          Other locales behave differently.  For example, in a German
          locale, `--time-style="locale"' might be equivalent to
          `--time-style="+%e. %b %Y $newline%e. %b %H:%M"' and might
          generate timestamps like `30. Ma"r 2002 ' and `30. Ma"r
          23:45'.

    `posix-STYLE'
          List POSIX-locale timestamps if the `LC_TIME' locale category
          is POSIX, STYLE timestamps otherwise.  For example, the
          `posix-long-iso' style lists timestamps like `Mar 30  2002'
          and `Mar 30 23:45' when in the POSIX locale, and like
          `2002-03-30 23:45' otherwise.

   You can specify the default value of the `--time-style' option with
the environment variable `TIME_STYLE'; if `TIME_STYLE' is not set the
default style is `locale'.  GNU Emacs 21.3 and later use the `--dired'
option and therefore can parse any date format, but if you are using
Emacs 21.1 or 21.2 and specify a non-POSIX locale you may need to set
`TIME_STYLE="posix-long-iso"'.

   To avoid certain denial-of-service attacks, timestamps that would be
longer than 1000 bytes may be treated as errors.


File: coreutils.info,  Node: Formatting the file names,  Prev: Formatting file timestamps,  Up: ls invocation

10.1.7 Formatting the file names
--------------------------------

These options change how file names themselves are printed.

`-b'
`--escape'
`--quoting-style=escape'
     Quote nongraphic characters in file names using alphabetic and
     octal backslash sequences like those used in C.

`-N'
`--literal'
`--quoting-style=literal'
     Do not quote file names.  However, with `ls' nongraphic characters
     are still printed as question marks if the output is a terminal
     and you do not specify the `--show-control-chars' option.

`-q'
`--hide-control-chars'
     Print question marks instead of nongraphic characters in file
     names.  This is the default if the output is a terminal and the
     program is `ls'.

`-Q'
`--quote-name'
`--quoting-style=c'
     Enclose file names in double quotes and quote nongraphic
     characters as in C.

`--quoting-style=WORD'
     Use style WORD to quote file names and other strings that may
     contain arbitrary characters.  The WORD should be one of the
     following:

    `literal'
          Output strings as-is; this is the same as the `-N' or
          `--literal' option.

    `shell'
          Quote strings for the shell if they contain shell
          metacharacters or would cause ambiguous output.  The quoting
          is suitable for POSIX-compatible shells like `bash', but it
          does not always work for incompatible shells like `csh'.

    `shell-always'
          Quote strings for the shell, even if they would normally not
          require quoting.

    `c'
          Quote strings as for C character string literals, including
          the surrounding double-quote characters; this is the same as
          the `-Q' or `--quote-name' option.

    `escape'
          Quote strings as for C character string literals, except omit
          the surrounding double-quote characters; this is the same as
          the `-b' or `--escape' option.

    `clocale'
          Quote strings as for C character string literals, except use
          surrounding quotation marks appropriate for the locale.

    `locale'
          Quote strings as for C character string literals, except use
          surrounding quotation marks appropriate for the locale, and
          quote `like this' instead of "like this" in the default C
          locale.  This looks nicer on many displays.

     You can specify the default value of the `--quoting-style' option
     with the environment variable `QUOTING_STYLE'.  If that environment
     variable is not set, the default value is `literal', but this
     default may change to `shell' in a future version of this package.

`--show-control-chars'
     Print nongraphic characters as-is in file names.  This is the
     default unless the output is a terminal and the program is `ls'.



File: coreutils.info,  Node: dir invocation,  Next: vdir invocation,  Prev: ls invocation,  Up: Directory listing

10.2 `dir': Briefly list directory contents
===========================================

`dir' is equivalent to `ls -C -b'; that is, by default files are listed
in columns, sorted vertically, and special characters are represented
by backslash escape sequences.

   *Note `ls': ls invocation.


File: coreutils.info,  Node: vdir invocation,  Next: dircolors invocation,  Prev: dir invocation,  Up: Directory listing

10.3 `vdir': Verbosely list directory contents
==============================================

`vdir' is equivalent to `ls -l -b'; that is, by default files are
listed in long format and special characters are represented by
backslash escape sequences.


File: coreutils.info,  Node: dircolors invocation,  Prev: vdir invocation,  Up: Directory listing

10.4 `dircolors': Color setup for `ls'
======================================

`dircolors' outputs a sequence of shell commands to set up the terminal
for color output from `ls' (and `dir', etc.).  Typical usage:

     eval "`dircolors [OPTION]... [FILE]`"

   If FILE is specified, `dircolors' reads it to determine which colors
to use for which file types and extensions.  Otherwise, a precompiled
database is used.  For details on the format of these files, run
`dircolors --print-database'.

   The output is a shell command to set the `LS_COLORS' environment
variable.  You can specify the shell syntax to use on the command line,
or `dircolors' will guess it from the value of the `SHELL' environment
variable.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--sh'
`--bourne-shell'
     Output Bourne shell commands.  This is the default if the `SHELL'
     environment variable is set and does not end with `csh' or `tcsh'.

`-c'
`--csh'
`--c-shell'
     Output C shell commands.  This is the default if `SHELL' ends with
     `csh' or `tcsh'.

`-p'
`--print-database'
     Print the (compiled-in) default color configuration database.  This
     output is itself a valid configuration file, and is fairly
     descriptive of the possibilities.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Basic operations,  Next: Special file types,  Prev: Directory listing,  Up: Top

11 Basic operations
*******************

This chapter describes the commands for basic file manipulation:
copying, moving (renaming), and deleting (removing).

* Menu:

* cp invocation::               Copy files.
* dd invocation::               Convert and copy a file.
* install invocation::          Copy files and set attributes.
* mv invocation::               Move (rename) files.
* rm invocation::               Remove files or directories.
* shred invocation::            Remove files more securely.


File: coreutils.info,  Node: cp invocation,  Next: dd invocation,  Up: Basic operations

11.1 `cp': Copy files and directories
=====================================

`cp' copies files (or, optionally, directories).  The copy is
completely independent of the original.  You can either copy one file to
another, or copy arbitrarily many files to a destination directory.
Synopses:

     cp [OPTION]... [-T] SOURCE DEST
     cp [OPTION]... SOURCE... DIRECTORY
     cp [OPTION]... -t DIRECTORY SOURCE...

   * If two file names are given, `cp' copies the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `cp' copies
     each SOURCE file to the specified directory, using the SOURCEs'
     names.

   Generally, files are written just as they are read.  For exceptions,
see the `--sparse' option below.

   By default, `cp' does not copy directories.  However, the `-R',
`-a', and `-r' options cause `cp' to copy recursively by descending
into source directories and copying files to corresponding destination
directories.

   By default, `cp' follows symbolic links only when not copying
recursively.  This default can be overridden with the `--archive'
(`-a'), `-d', `--dereference' (`-L'), `--no-dereference' (`-P'), and
`-H' options.  If more than one of these options is specified, the last
one silently overrides the others.

   By default, `cp' copies the contents of special files only when not
copying recursively.  This default can be overridden with the
`--copy-contents' option.

   `cp' generally refuses to copy a file onto itself, with the
following exception: if `--force --backup' is specified with SOURCE and
DEST identical, and referring to a regular file, `cp' will make a
backup file, either regular or numbered, as specified in the usual ways
(*note Backup options::).  This is useful when you simply want to make
a backup of an existing file before changing it.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--archive'
     Preserve as much as possible of the structure and attributes of the
     original files in the copy (but do not attempt to preserve internal
     directory structure; i.e., `ls -U' may list the entries in a copied
     directory in a different order).  Equivalent to `-dpPR'.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.  As a special case, `cp'
     makes a backup of SOURCE when the force and backup options are
     given and SOURCE and DEST are the same name for an existing,
     regular file.  One useful application of this combination of
     options is this tiny Bourne shell script:

          #!/bin/sh
          # Usage: backup FILE...
          # Create a GNU-style backup of each listed FILE.
          for i; do
            cp --backup --force -- "$i" "$i"
          done

`--copy-contents'
     If copying recursively, copy the contents of any special files
     (e.g., FIFOs and device files) as if they were regular files.
     This means trying to read the data in each source file and writing
     it to the destination.  It is usually a mistake to use this
     option, as it normally has undesirable effects on special files
     like FIFOs and the ones typically found in the `/dev' directory.
     In most cases, `cp -R --copy-contents' will hang indefinitely
     trying to read from FIFOs and special files like `/dev/console',
     and it will fill up your destination disk if you use it to copy
     `/dev/zero'.  This option has no effect unless copying
     recursively, and it does not affect the copying of symbolic links.

`-d'
     Copy symbolic links as symbolic links rather than copying the
     files that they point to, and preserve hard links between source
     files in the copies.  Equivalent to `--no-dereference
     --preserve=links'.

`-f'
`--force'
     When copying without this option and an existing destination file
     cannot be opened for writing, the copy fails.  However, with
     `--force'), when a destination file cannot be opened, `cp' then
     unlinks it and tries to open it again.  Contrast this behavior
     with that enabled by `--link' and `--symbolic-link', whereby the
     destination file is never opened but rather is unlinked
     unconditionally.  Also see the description of
     `--remove-destination'.

     This option is independent of the `--interactive' or `-i' option:
     neither cancels the effect of the other.

`-H'
     If a command line argument specifies a symbolic link, then copy the
     file it points to rather than the symbolic link itself.  However,
     copy (preserving its nature) any symbolic link that is encountered
     via recursive traversal.

`-i'
`--interactive'
     When copying a file other than a directory, prompt whether to
     overwrite an existing destination file.

`-l'
`--link'
     Make hard links instead of copies of non-directories.

`-L'
`--dereference'
     Always follow symbolic links.

`-P'
`--no-dereference'
     Copy symbolic links as symbolic links rather than copying the
     files that they point to.

`-p'
`--preserve[=ATTRIBUTE_LIST]'
     Preserve the specified attributes of the original files.  If
     specified, the ATTRIBUTE_LIST must be a comma-separated list of
     one or more of the following strings:

    `mode'
          Preserve the file mode bits and access control lists.

    `ownership'
          Preserve the owner and group.  On most modern systems, only
          users with appropriate privileges may change the owner of a
          file, and ordinary users may preserve the group ownership of
          a file only if they happen to be a member of the desired
          group.

    `timestamps'
          Preserve the times of last access and last modification, when
          possible.  In general, it is not possible to preserve these
          attributes when the affected file is a symbolic link.
          However, FreeBSD now provides the `lutimes' function, which
          makes it possibile even for symbolic links.  However, this
          implementation does not yet take advantage of that.

    `links'
          Preserve in the destination files any links between
          corresponding source files.

    `all'
          Preserve all file attributes.  Equivalent to specifying all
          of the above.

     Using `--preserve' with no ATTRIBUTE_LIST is equivalent to
     `--preserve=mode,ownership,timestamps'.

     In the absence of this option, each destination file is created
     with the mode bits of the corresponding source file, minus the
     bits set in the umask and minus the set-user-ID and set-group-ID
     bits.  *Note File permissions::.

`--no-preserve=ATTRIBUTE_LIST'
     Do not preserve the specified attributes.  The ATTRIBUTE_LIST has
     the same form as for `--preserve'.

`--parents'
     Form the name of each destination file by appending to the target
     directory a slash and the specified name of the source file.  The
     last argument given to `cp' must be the name of an existing
     directory.  For example, the command:

          cp --parents a/b/c existing_dir

     copies the file `a/b/c' to `existing_dir/a/b/c', creating any
     missing intermediate directories.

`--reply=HOW'
     *Deprecated: to be removed in 2008.*
     Using `--reply=yes' makes `cp' act as if `yes' were given as a
     response to every prompt about a destination file.  That
     effectively cancels any preceding `--interactive' or `-i' option.
     Specify `--reply=no' to make `cp' act as if `no' were given as a
     response to every prompt about a destination file.  Specify
     `--reply=query' to make `cp' prompt the user about each existing
     destination file.

`-R'
`-r'
`--recursive'
     Copy directories recursively.  Symbolic links are not followed by
     default; see the `--archive' (`-a'), `-d', `--dereference' (`-L'),
     `--no-dereference' (`-P'), and `-H' options.  Special files are
     copied by creating a destination file of the same type as the
     source; see the `--copy-contents' option.  It is not portable to
     use `-r' to copy symbolic links or special files.  On some non-GNU
     systems, `-r' implies the equivalent of `-L' and `--copy-contents'
     for historical reasons.  Also, it is not portable to use `-R' to
     copy symbolic links unless you also specify `-P', as POSIX allows
     implementations that dereference symbolic links by default.

`--remove-destination'
     Remove each existing destination file before attempting to open it
     (contrast with `-f' above).

`--sparse=WHEN'
     A "sparse file" contains "holes"--a sequence of zero bytes that
     does not occupy any physical disk blocks; the `read' system call
     reads these as zeros.  This can both save considerable disk space
     and increase speed, since many binary files contain lots of
     consecutive zero bytes.  By default, `cp' detects holes in input
     source files via a crude heuristic and makes the corresponding
     output file sparse as well.  Only regular files may be sparse.

     The WHEN value can be one of the following:

    `auto'
          The default behavior: if the input file is sparse, attempt to
          make the output file sparse, too.  However, if an output file
          exists but refers to a non-regular file, then do not attempt
          to make it sparse.

    `always'
          For each sufficiently long sequence of zero bytes in the
          input file, attempt to create a corresponding hole in the
          output file, even if the input file does not appear to be
          sparse.  This is useful when the input file resides on a file
          system that does not support sparse files (for example,
          `efs' file systems in SGI IRIX 5.3 and earlier), but the
          output file is on a type of file system that does support
          them.  Holes may be created only in regular files, so if the
          destination file is of some other type, `cp' does not even
          try to make it sparse.

    `never'
          Never make the output file sparse.  This is useful in
          creating a file for use with the `mkswap' command, since such
          a file must not have any holes.

`--strip-trailing-slashes'
     Remove any trailing slashes from each SOURCE argument.  *Note
     Trailing slashes::.

`-s'
`--symbolic-link'
     Make symbolic links instead of copies of non-directories.  All
     source file names must be absolute (starting with `/') unless the
     destination files are in the current directory.  This option merely
     results in an error message on systems that do not support
     symbolic links.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-u'
`--update'
     Do not copy a non-directory that has an existing destination with
     the same or newer modification time.  If time stamps are being
     preserved, the comparison is to the source time stamp truncated to
     the resolutions of the destination file system and of the system
     calls used to update time stamps; this avoids duplicate work if
     several `cp -pu' commands are executed with the same source and
     destination.

`-v'
`--verbose'
     Print the name of each file before copying it.

`-x'
`--one-file-system'
     Skip subdirectories that are on different file systems from the
     one that the copy started on.  However, mount point directories
     _are_ copied.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: dd invocation,  Next: install invocation,  Prev: cp invocation,  Up: Basic operations

11.2 `dd': Convert and copy a file
==================================

`dd' copies a file (from standard input to standard output, by default)
with a changeable I/O block size, while optionally performing
conversions on it.  Synopses:

     dd [OPERAND]...
     dd OPTION

   The only options are `--help' and `--version'.  *Note Common
options::.  `dd' accepts the following operands.

`if=FILE'
     Read from FILE instead of standard input.

`of=FILE'
     Write to FILE instead of standard output.  Unless `conv=notrunc'
     is given, `dd' truncates FILE to zero bytes (or the size specified
     with `seek=').

`ibs=BYTES'
     Set the input block size to BYTES.  This makes `dd' read BYTES per
     block.

`obs=BYTES'
     Set the output block size to BYTES.  This makes `dd' write BYTES
     per block.

`bs=BYTES'
     Set both input and output block sizes to BYTES.  This makes `dd'
     read and write BYTES per block, overriding any `ibs' and `obs'
     settings.

`cbs=BYTES'
     Set the conversion block size to BYTES.  When converting
     variable-length records to fixed-length ones (`conv=block') or the
     reverse (`conv=unblock'), use BYTES as the fixed record length.

`skip=BLOCKS'
     Skip BLOCKS `ibs'-byte blocks in the input file before copying.

`seek=BLOCKS'
     Skip BLOCKS `obs'-byte blocks in the output file before copying.

`count=BLOCKS'
     Copy BLOCKS `ibs'-byte blocks from the input file, instead of
     everything until the end of the file.

`conv=CONVERSION[,CONVERSION]...'
     Convert the file as specified by the CONVERSION argument(s).  (No
     spaces around any comma(s).)

     Conversions:

    `ascii'
          Convert EBCDIC to ASCII, using the conversion table specified
          by POSIX.  This provides a 1:1 translation for all 256 bytes.

    `ebcdic'
          Convert ASCII to EBCDIC.  This is the inverse of the `ascii'
          conversion.

    `ibm'
          Convert ASCII to alternate EBCDIC, using the alternate
          conversion table specified by POSIX.  This is not a 1:1
          translation, but reflects common historical practice for `~',
          `[', and `]'.

          The `ascii', `ebcdic', and `ibm' conversions are mutually
          exclusive.

    `block'
          For each line in the input, output `cbs' bytes, replacing the
          input newline with a space and padding with spaces as
          necessary.

    `unblock'
          Replace trailing spaces in each `cbs'-sized input block with a
          newline.

          The `block' and `unblock' conversions are mutually exclusive.

    `lcase'
          Change uppercase letters to lowercase.

    `ucase'
          Change lowercase letters to uppercase.

          The `lcase' and `ucase' conversions are mutually exclusive.

    `swab'
          Swap every pair of input bytes.  GNU `dd', unlike others,
          works when an odd number of bytes are read--the last byte is
          simply copied (since there is nothing to swap it with).

    `noerror'
          Continue after read errors.

    `nocreat'
          Do not create the output file; the output file must already
          exist.

    `excl'
          Fail if the output file already exists; `dd' must create the
          output file itself.

          The `excl' and `nocreat' conversions are mutually exclusive.

    `notrunc'
          Do not truncate the output file.

    `sync'
          Pad every input block to size of `ibs' with trailing zero
          bytes.  When used with `block' or `unblock', pad with spaces
          instead of zero bytes.

    `fdatasync'
          Synchronize output data just before finishing.  This forces a
          physical write of output data.

    `fsync'
          Synchronize output data and metadata just before finishing.
          This forces a physical write of output data and metadata.


`iflag=FLAG[,FLAG]...'
     Access the input file using the flags specified by the FLAG
     argument(s).  (No spaces around any comma(s).)

`oflag=FLAG[,FLAG]...'
     Access the output file using the flags specified by the FLAG
     argument(s).  (No spaces around any comma(s).)

     Here are the flags.  Not every flag is supported on every operating
     system.

    `append'
          Write in append mode, so that even if some other process is
          writing to this file, every `dd' write will append to the
          current contents of the file.  This flag makes sense only for
          output.  If you combine this flag with the `of=FILE' operand,
          you should also specify `conv=notrunc' unless you want the
          output file to be truncated before being appended to.

    `direct'
          Use direct I/O for data, avoiding the buffer cache.

    `directory'
          Fail unless the file is a directory.  Most operating systems
          do not allow I/O to a directory, so this flag has limited
          utility.

    `dsync'
          Use synchronized I/O for data.  For the output file, this
          forces a physical write of output data on each write.  For
          the input file, this flag can matter when reading from a
          remote file that has been written to synchronously by some
          other process.  Metadata (e.g., last-access and last-modified
          time) is not necessarily synchronized.

    `sync'
          Use synchronized I/O for both data and metadata.

    `nonblock'
          Use non-blocking I/O.

    `noatime'
          Do not update the file's access time.  Some older file
          systems silently ignore this flag, so it is a good idea to
          test it on your files before relying on it.

    `noctty'
          Do not assign the file to be a controlling terminal for `dd'.
          This has no effect when the file is not a terminal.  On many
          hosts (e.g., GNU/Linux hosts), this option has no effect at
          all.

    `nofollow'
          Do not follow symbolic links.

    `nolinks'
          Fail if the file has multiple hard links.

    `binary'
          Use binary I/O.  This option has an effect only on nonstandard
          platforms that distinguish binary from text I/O.

    `text'
          Use text I/O.  Like `binary', this option has no effect on
          standard platforms.


     These flags are not supported on all systems, and `dd' rejects
     attempts to use them when they are not supported.  When reading
     from standard input or writing to standard output, the `nofollow'
     and `noctty' flags should not be specified, and the other flags
     (e.g., `nonblock') can affect how other processes behave with the
     affected file descriptors, even after `dd' exits.


   The numeric-valued strings above (BYTES and BLOCKS) can be followed
by a multiplier: `b'=512, `c'=1, `w'=2, `xM'=M, or any of the standard
block size suffixes like `k'=1024 (*note Block size::).

   Use different `dd' invocations to use different block sizes for
skipping and I/O.  For example, the following shell commands copy data
in 512 KiB blocks between a disk and a tape, but do not save or restore
a 4 KiB label at the start of the disk:

     disk=/dev/rdsk/c0t1d0s2
     tape=/dev/rmt/0

     # Copy all but the label from disk to tape.
     (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape

     # Copy from tape back to disk, but leave the disk label alone.
     (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk

   Sending an `INFO' signal to a running `dd' process makes it print
I/O statistics to standard error and then resume copying.  In the
example below, `dd' is run in the background to copy 10 million blocks.
The `kill' command makes it output intermediate I/O statistics, and
when `dd' completes, it outputs the final statistics.

     $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
     $ kill -s INFO $pid; wait $pid
     3385223+0 records in
     3385223+0 records out
     1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
     10000000+0 records in
     10000000+0 records out
     5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s

   On systems lacking the `INFO' signal `dd' responds to the `USR1'
signal instead, unless the `POSIXLY_CORRECT' environment variable is
set.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: install invocation,  Next: mv invocation,  Prev: dd invocation,  Up: Basic operations

11.3 `install': Copy files and set attributes
=============================================

`install' copies files while setting their file mode bits and, if
possible, their owner and group.  Synopses:

     install [OPTION]... [-T] SOURCE DEST
     install [OPTION]... SOURCE... DIRECTORY
     install [OPTION]... -t DIRECTORY SOURCE...
     install [OPTION]... -d DIRECTORY...

   * If two file names are given, `install' copies the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `install'
     copies each SOURCE file to the specified directory, using the
     SOURCEs' names.

   * If the `--directory' (`-d') option is given, `install' creates
     each DIRECTORY and any missing parent directories.  Parent
     directories are created with mode `u=rwx,go=rx' (755), regardless
     of the `-m' option or the current umask.  *Note Directory Setuid
     and Setgid::, for how the set-user-ID and set-group-ID bits of
     parent directories are inherited.

   `install' is similar to `cp', but allows you to control the
attributes of destination files.  It is typically used in Makefiles to
copy programs into their destination directories.  It refuses to copy
files onto themselves.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-c'
     Ignored; for compatibility with old Unix versions of `install'.

`-d'
`--directory'
     Create any missing parent directories, giving them the default
     attributes.  Then create each given directory, setting their owner,
     group and mode as given on the command line or to the defaults.

`-g GROUP'
`--group=GROUP'
     Set the group ownership of installed files or directories to
     GROUP.  The default is the process's current group.  GROUP may be
     either a group name or a numeric group ID.

`-m MODE'
`--mode=MODE'
     Set the file mode bits for the installed file or directory to MODE,
     which can be either an octal number, or a symbolic mode as in
     `chmod', with `a=' (no access allowed to anyone) as the point of
     departure (*note File permissions::).  The default mode is
     `u=rwx,go=rx,a-s'--read, write, and execute for the owner, read
     and execute for group and other, and with set-user-ID and
     set-group-ID disabled.  This default is not quite the same as
     `755', since it disables instead of preserving set-user-ID and
     set-group-ID on directories.  *Note Directory Setuid and Setgid::.

`-o OWNER'
`--owner=OWNER'
     If `install' has appropriate privileges (is run as root), set the
     ownership of installed files or directories to OWNER.  The default
     is `root'.  OWNER may be either a user name or a numeric user ID.

`-p'
`--preserve-timestamps'
     Set the time of last access and the time of last modification of
     each installed file to match those of each corresponding original
     file.  When a file is installed without this option, its last
     access and last modification times are both set to the time of
     installation.  This option is useful if you want to use the last
     modification times of installed files to keep track of when they
     were last built as opposed to when they were last installed.

`-s'
`--strip'
     Strip the symbol tables from installed binary executables.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-v'
`--verbose'
     Print the name of each file before copying it.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: mv invocation,  Next: rm invocation,  Prev: install invocation,  Up: Basic operations

11.4 `mv': Move (rename) files
==============================

`mv' moves or renames files (or directories).  Synopses:

     mv [OPTION]... [-T] SOURCE DEST
     mv [OPTION]... SOURCE... DIRECTORY
     mv [OPTION]... -t DIRECTORY SOURCE...

   * If two file names are given, `mv' moves the first file to the
     second.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `mv' moves
     each SOURCE file to the specified directory, using the SOURCEs'
     names.

   `mv' can move any type of file from one file system to another.
Prior to version `4.0' of the fileutils, `mv' could move only regular
files between file systems.  For example, now `mv' can move an entire
directory hierarchy including special device files from one partition
to another.  It first uses some of the same code that's used by `cp -a'
to copy the requested directories and files, then (assuming the copy
succeeded) it removes the originals.  If the copy fails, then the part
that was copied to the destination partition is removed.  If you were
to copy three directories from one partition to another and the copy of
the first directory succeeded, but the second didn't, the first would
be left on the destination partition and the second and third would be
left on the original partition.

   If a destination file exists but is normally unwritable, standard
input is a terminal, and the `-f' or `--force' option is not given,
`mv' prompts the user for whether to replace the file.  (You might own
the file, or have write permission on its directory.)  If the response
is not affirmative, the file is skipped.

   _Warning_: If you try to move a symlink that points to a directory,
and you specify the symlink with a trailing slash, then `mv' doesn't
move the symlink but instead moves the directory referenced by the
symlink.  *Note Trailing slashes::.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-f'
`--force'
     Do not prompt the user before removing a destination file.

`-i'
`--interactive'
     Prompt whether to overwrite each existing destination file,
     regardless of its permissions.  If the response is not
     affirmative, the file is skipped.

`--reply=HOW'
     *Deprecated: to be removed in 2008.*
     Specifying `--reply=yes' is equivalent to using `--force'.
     Specify `--reply=no' to make `mv' act as if `no' were given as a
     response to every prompt about a destination file.  Specify
     `--reply=query' to make `mv' prompt the user about each existing
     destination file.  Note that `--reply=no' has an effect only when
     `mv' would prompt without `-i' or equivalent, i.e., when a
     destination file exists and is not writable, standard input is a
     terminal, and no `-f' (or equivalent) option is specified.

`-u'
`--update'
     Do not move a non-directory that has an existing destination with
     the same or newer modification time.  If the move is across file
     system boundaries, the comparison is to the source time stamp
     truncated to the resolutions of the destination file system and of
     the system calls used to update time stamps; this avoids duplicate
     work if several `mv -u' commands are executed with the same source
     and destination.

`-v'
`--verbose'
     Print the name of each file before moving it.

`--strip-trailing-slashes'
     Remove any trailing slashes from each SOURCE argument.  *Note
     Trailing slashes::.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: rm invocation,  Next: shred invocation,  Prev: mv invocation,  Up: Basic operations

11.5 `rm': Remove files or directories
======================================

`rm' removes each given FILE.  By default, it does not remove
directories.  Synopsis:

     rm [OPTION]... [FILE]...

   If the `-I' or `--interactive=once' option is given, and there are
more than three files or the `-r', `-R', or `--recursive' are given,
then `rm' prompts the user for whether to proceed with the entire
operation.  If the response is not affirmative, the entire command is
aborted.

   Otherwise, if a file is unwritable, standard input is a terminal, and
the `-f' or `--force' option is not given, or the `-i' or
`--interactive=always' option _is_ given, `rm' prompts the user for
whether to remove the file.  If the response is not affirmative, the
file is skipped.

   Any attempt to remove a file whose last file name component is `.'
or `..' is rejected without any prompting.

   _Warning_: If you use `rm' to remove a file, it is usually possible
to recover the contents of that file.  If you want more assurance that
the contents are truly unrecoverable, consider using `shred'.

   The program accepts the following options.  Also see *Note Common
options::.

`-f'
`--force'
     Ignore nonexistent files and never prompt the user.  Ignore any
     previous `--interactive' (`-i') option.

`-i'
     Prompt whether to remove each file.  If the response is not
     affirmative, the file is skipped.  Ignore any previous `--force'
     (`-f') option.  Equivalent to `--interactive=always'.

`-I'
     Prompt once whether to proceed with the command, if more than three
     files are named or if a recursive removal is requested.  Ignore any
     previous `--force' (`-f') option.  Equivalent to
     `--interactive=once'.

`--interactive [=WHEN]'
     Specify when to issue an interactive prompt.  WHEN may be omitted,
     or one of:
        * never - Do not prompt at all.

        * once - Prompt once if more than three files are named or if a
          recursive removal is requested.  Equivalent to `-I'.

        * always - Prompt for every file being removed.  Equivalent to
          `-i'.
     Specifying `--interactive' and no WHEN is equivalent to
     `--interactive=always'.

`--one-file-system'
     When removing a hierarchy recursively, skip any directory that is
     on a file system different from that of the corresponding command
     line argument.

     This option is useful when removing a build "chroot" hierarchy,
     which normally contains no valuable data.  However, it is not
     uncommon to bind-mount `/home' into such a hierarchy, to make it
     easier to use one's start-up file.  The catch is that it's easy to
     forget to unmount `/home'.  Then, when you use `rm -rf' to remove
     your normally throw-away chroot, that command will remove
     everything under `/home', too.  Use the `--one-file-system'
     option, and it will warn about and skip directories on other file
     systems.  Of course, this will not save your `/home' if it and your
     chroot happen to be on the same file system.

`--preserve-root'
     Fail upon any attempt to remove the root directory, `/', when used
     with the `--recursive' option.  This is the default behavior.
     *Note Treating / specially::.

`--no-preserve-root'
     Do not treat `/' specially when removing recursively.  This option
     is not recommended unless you really want to remove all the files
     on your computer.  *Note Treating / specially::.

`-r'
`-R'
`--recursive'
     Remove the listed directories and their contents recursively.

`-v'
`--verbose'
     Print the name of each file before removing it.


   One common question is how to remove files whose names begin with a
`-'.  GNU `rm', like every program that uses the `getopt' function to
parse its arguments, lets you use the `--' option to indicate that all
following arguments are non-options.  To remove a file called `-f' in
the current directory, you could type either:

     rm -- -f

or:

     rm ./-f

   The Unix `rm' program's use of a single `-' for this purpose
predates the development of the getopt standard syntax.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: shred invocation,  Prev: rm invocation,  Up: Basic operations

11.6 `shred': Remove files more securely
========================================

`shred' overwrites devices or files, to help prevent even very
expensive hardware from recovering the data.

   Ordinarily when you remove a file (*note rm invocation::), the data
is not actually destroyed.  Only the index listing where the file is
stored is destroyed, and the storage is made available for reuse.
There are undelete utilities that will attempt to reconstruct the index
and can bring the file back if the parts were not reused.

   On a busy system with a nearly-full drive, space can get reused in a
few seconds.  But there is no way to know for sure.  If you have
sensitive data, you may want to be sure that recovery is not possible
by actually overwriting the file with non-sensitive data.

   However, even after doing that, it is possible to take the disk back
to a laboratory and use a lot of sensitive (and expensive) equipment to
look for the faint "echoes" of the original data underneath the
overwritten data.  If the data has only been overwritten once, it's not
even that hard.

   The best way to remove something irretrievably is to destroy the
media it's on with acid, melt it down, or the like.  For cheap
removable media like floppy disks, this is the preferred method.
However, hard drives are expensive and hard to melt, so the `shred'
utility tries to achieve a similar effect non-destructively.

   This uses many overwrite passes, with the data patterns chosen to
maximize the damage they do to the old data.  While this will work on
floppies, the patterns are designed for best effect on hard drives.
For more details, see the source code and Peter Gutmann's paper `Secure
Deletion of Data from Magnetic and Solid-State Memory'
(http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html), from the
proceedings of the Sixth USENIX Security Symposium (San Jose,
California, July 22-25, 1996).

   *Please note* that `shred' relies on a very important assumption:
that the file system overwrites data in place.  This is the traditional
way to do things, but many modern file system designs do not satisfy
this assumption.  Exceptions include:

   * Log-structured or journaled file systems, such as those supplied
     with AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in
     `data=journal' mode), BFS, NTFS, etc. when they are configured to
     journal _data_.

   * File systems that write redundant data and carry on even if some
     writes fail, such as RAID-based file systems.

   * File systems that make snapshots, such as Network Appliance's NFS
     server.

   * File systems that cache in temporary locations, such as NFS
     version 3 clients.

   * Compressed file systems.

   In the particular case of ext3 file systems, the above disclaimer
applies (and `shred' is thus of limited effectiveness) only in
`data=journal' mode, which journals file data in addition to just
metadata. In both the `data=ordered' (default) and `data=writeback'
modes, `shred' works as usual.  Ext3 journaling modes can be changed by
adding the `data=something' option to the mount options for a
particular file system in the `/etc/fstab' file, as documented in the
mount man page (man mount).

   If you are not sure how your file system operates, then you should
assume that it does not overwrite data in place, which means that shred
cannot reliably operate on regular files in your file system.

   Generally speaking, it is more reliable to shred a device than a
file, since this bypasses the problem of file system design mentioned
above.  However, even shredding devices is not always completely
reliable.  For example, most disks map out bad sectors invisibly to the
application; if the bad sectors contain sensitive data, `shred' won't
be able to destroy it.

   `shred' makes no attempt to detect or report this problem, just as
it makes no attempt to do anything about backups.  However, since it is
more reliable to shred devices than files, `shred' by default does not
truncate or remove the output file.  This default is more suitable for
devices, which typically cannot be truncated and should not be removed.

   Finally, consider the risk of backups and mirrors.  File system
backups and remote mirrors may contain copies of the file that cannot
be removed, and that will allow a shredded file to be recovered later.
So if you keep any data you may later want to destroy using `shred', be
sure that it is not backed up or mirrored.

     shred [OPTION]... FILE[...]

   The program accepts the following options.  Also see *Note Common
options::.

`-f'
`--force'
     Override file permissions if necessary to allow overwriting.

`-NUMBER'
`-n NUMBER'
`--iterations=NUMBER'
     By default, `shred' uses 25 passes of overwrite.  This is enough
     for all of the useful overwrite patterns to be used at least once.
     You can reduce this to save time, or increase it if you have a lot
     of time to waste.

`--random-source=FILE'
     Use FILE as a source of random data used to overwrite and to
     choose pass ordering.  *Note Random sources::.

`-s BYTES'
`--size=BYTES'
     Shred the first BYTES bytes of the file.  The default is to shred
     the whole file.  BYTES can be followed by a size specification like
     `K', `M', or `G' to specify a multiple.  *Note Block size::.

`-u'
`--remove'
     After shredding a file, truncate it (if possible) and then remove
     it.  If a file has multiple links, only the named links will be
     removed.

`-v'
`--verbose'
     Display status updates as sterilization proceeds.

`-x'
`--exact'
     By default, `shred' rounds the size of a regular file up to the
     next multiple of the file system block size to fully erase the
     last block of the file.  Use `--exact' to suppress that behavior.
     Thus, by default if you shred a 10-byte regular file on a system
     with 512-byte blocks, the resulting file will be 512 bytes long.
     With this option, shred does not increase the apparent size of the
     file.

`-z'
`--zero'
     Normally, the last pass that `shred' writes is made up of random
     data.  If this would be conspicuous on your hard drive (for
     example, because it looks like encrypted data), or you just think
     it's tidier, the `--zero' option adds an additional overwrite pass
     with all zero bits.  This is in addition to the number of passes
     specified by the `--iterations' option.


   You might use the following command to erase all trace of the file
system you'd created on the floppy disk in your first drive.  That
command takes about 20 minutes to erase a "1.44MB" (actually 1440 KiB)
floppy.

     shred --verbose /dev/fd0

   Similarly, to erase all data on a selected partition of your hard
disk, you could give a command like this:

     shred --verbose /dev/sda5

   A FILE of `-' denotes standard output.  The intended use of this is
to shred a removed temporary file.  For example:

     i=`tempfile -m 0600`
     exec 3<>"$i"
     rm -- "$i"
     echo "Hello, world" >&3
     shred - >&3
     exec 3>-

   However, the command `shred - >file' does not shred the contents of
FILE, since the shell truncates FILE before invoking `shred'.  Use the
command `shred file' or (if using a Bourne-compatible shell) the
command `shred - 1<>file' instead.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Special file types,  Next: Changing file attributes,  Prev: Basic operations,  Up: Top

12 Special file types
*********************

This chapter describes commands which create special types of files (and
`rmdir', which removes directories, one special file type).

   Although Unix-like operating systems have markedly fewer special file
types than others, not _everything_ can be treated only as the
undifferentiated byte stream of "normal files".  For example, when a
file is created or removed, the system must record this information,
which it does in a "directory"--a special type of file.  Although you
can read directories as normal files, if you're curious, in order for
the system to do its job it must impose a structure, a certain order,
on the bytes of the file.  Thus it is a "special" type of file.

   Besides directories, other special file types include named pipes
(FIFOs), symbolic links, sockets, and so-called "special files".

* Menu:

* link invocation::             Make a hard link via the link syscall
* ln invocation::               Make links between files.
* mkdir invocation::            Make directories.
* mkfifo invocation::           Make FIFOs (named pipes).
* mknod invocation::            Make block or character special files.
* readlink invocation::         Print the referent of a symbolic link.
* rmdir invocation::            Remove empty directories.
* unlink invocation::           Remove files via the unlink syscall


File: coreutils.info,  Node: link invocation,  Next: ln invocation,  Up: Special file types

12.1 `link': Make a hard link via the link syscall
==================================================

`link' creates a single hard link at a time.  It is a minimalist
interface to the system-provided `link' function.  *Note Hard Links:
(libc)Hard Links.  It avoids the bells and whistles of the more
commonly-used `ln' command (*note ln invocation::).  Synopsis:

     link FILENAME LINKNAME

   FILENAME must specify an existing file, and LINKNAME must specify a
nonexistent entry in an existing directory.  `link' simply calls `link
(FILENAME, LINKNAME)' to create the link.

   On a GNU system, this command acts like `ln --directory
--no-target-directory FILENAME LINKNAME'.  However, the `--directory'
and `--no-target-directory' options are not specified by POSIX, and the
`link' command is more portable in practice.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: ln invocation,  Next: mkdir invocation,  Prev: link invocation,  Up: Special file types

12.2 `ln': Make links between files
===================================

`ln' makes links between files.  By default, it makes hard links; with
the `-s' option, it makes symbolic (or "soft") links.  Synopses:

     ln [OPTION]... [-T] TARGET LINKNAME
     ln [OPTION]... TARGET
     ln [OPTION]... TARGET... DIRECTORY
     ln [OPTION]... -t DIRECTORY TARGET...

   * If two file names are given, `ln' creates a link to the first file
     from the second.

   * If one TARGET is given, `ln' creates a link to that file in the
     current directory.

   * If the `--target-directory' (`-t') option is given, or failing
     that if the last file is a directory and the
     `--no-target-directory' (`-T') option is not given, `ln' creates a
     link to each TARGET file in the specified directory, using the
     TARGETs' names.


   Normally `ln' does not remove existing files.  Use the `--force'
(`-f') option to remove them unconditionally, the `--interactive'
(`-i') option to remove them conditionally, and the `--backup' (`-b')
option to rename them.

   A "hard link" is another name for an existing file; the link and the
original are indistinguishable.  Technically speaking, they share the
same inode, and the inode contains all the information about a
file--indeed, it is not incorrect to say that the inode _is_ the file.
On all existing implementations, you cannot make a hard link to a
directory, and hard links cannot cross file system boundaries.  (These
restrictions are not mandated by POSIX, however.)

   "Symbolic links" ("symlinks" for short), on the other hand, are a
special file type (which not all kernels support: System V release 3
(and older) systems lack symlinks) in which the link file actually
refers to a different file, by name.  When most operations (opening,
reading, writing, and so on) are passed the symbolic link file, the
kernel automatically "dereferences" the link and operates on the target
of the link.  But some operations (e.g., removing) work on the link
file itself, rather than on its target.  *Note Symbolic Links:
(libc)Symbolic Links.

   The program accepts the following options.  Also see *Note Common
options::.

`-b'
`--backup[=METHOD]'
     *Note Backup options::.  Make a backup of each file that would
     otherwise be overwritten or removed.

`-d'
`-F'
`--directory'
     Allow users with appropriate privileges to attempt to make hard
     links to directories.  However, note that this will probably fail
     due to system restrictions, even for the super-user.

`-f'
`--force'
     Remove existing destination files.

`-i'
`--interactive'
     Prompt whether to remove existing destination files.

`-n'
`--no-dereference'
     Do not treat the last operand specially when it is a symbolic link
     to a directory.  Instead, treat it as if it were a normal file.

     When the destination is an actual directory (not a symlink to one),
     there is no ambiguity.  The link is created in that directory.
     But when the specified destination is a symlink to a directory,
     there are two ways to treat the user's request.  `ln' can treat
     the destination just as it would a normal directory and create the
     link in it.  On the other hand, the destination can be viewed as a
     non-directory--as the symlink itself.  In that case, `ln' must
     delete or backup that symlink before creating the new link.  The
     default is to treat a destination that is a symlink to a directory
     just like a directory.

     This option is weaker than the `--no-target-directory' (`-T')
     option, so it has no effect if both options are given.

`-s'
`--symbolic'
     Make symbolic links instead of hard links.  This option merely
     produces an error message on systems that do not support symbolic
     links.

`-S SUFFIX'
`--suffix=SUFFIX'
     Append SUFFIX to each backup file made with `-b'.  *Note Backup
     options::.

`-t DIRECTORY'
`--target-directory=DIRECTORY'
     Specify the destination DIRECTORY.  *Note Target directory::.

`-T'
`--no-target-directory'
     Do not treat the last operand specially when it is a directory or a
     symbolic link to a directory.  *Note Target directory::.

`-v'
`--verbose'
     Print the name of each file after linking it successfully.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     Bad Example:

     # Create link ../a pointing to a in that directory.
     # Not really useful because it points to itself.
     ln -s a ..

     Better Example:

     # Change to the target before creating symlinks to avoid being confused.
     cd ..
     ln -s adir/a .

     Bad Example:

     # Hard coded file names don't move well.
     ln -s $(pwd)/a /some/dir/

     Better Example:

     # Relative file names survive directory moves and also
     # work across networked file systems.
     ln -s afile anotherfile
     ln -s ../adir/afile yetanotherfile


File: coreutils.info,  Node: mkdir invocation,  Next: mkfifo invocation,  Prev: ln invocation,  Up: Special file types

12.3 `mkdir': Make directories
==============================

`mkdir' creates directories with the specified names.  Synopsis:

     mkdir [OPTION]... NAME...

   `mkdir' creates each directory NAME in the order given.  It reports
an error if NAME already exists, unless the `-p' option is given and
NAME is a directory.

   The program accepts the following options.  Also see *Note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the file permission bits of created directories to MODE, which
     uses the same syntax as in `chmod' and uses `a=rwx' (read, write
     and execute allowed for everyone) for the point of the departure.
     *Note File permissions::.

     Normally the directory has the desired file mode bits at the
     moment it is created.  As a GNU extension, MODE may also mention
     special mode bits, but in this case there may be a temporary window
     during which the directory exists but its special mode bits are
     incorrect.  *Note Directory Setuid and Setgid::, for how the
     set-user-ID and set-group-ID bits of directories are inherited
     unless overridden in this way.

`-p'
`--parents'
     Make any missing parent directories for each argument, setting
     their file permission bits to the umask modified by `u+wx'.  Ignore
     existing parent directories, and do not change their file
     permission bits.

     To set the file permission bits of any newly-created parent
     directories to a value that includes `u+wx', you can set the umask
     before invoking `mkdir'.  For example, if the shell command
     `(umask u=rwx,go=rx; mkdir -p P/Q)' creates the parent `P' it sets
     the parent's permission bits to `u=rwx,go=rx'.  To set a parent's
     special mode bits as well, you can invoke `chmod' after `mkdir'.
     *Note Directory Setuid and Setgid::, for how the set-user-ID and
     set-group-ID bits of newly-created parent directories are
     inherited.

`-v'
`--verbose'
     Print a message for each created directory.  This is most useful
     with `--parents'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: mkfifo invocation,  Next: mknod invocation,  Prev: mkdir invocation,  Up: Special file types

12.4 `mkfifo': Make FIFOs (named pipes)
=======================================

`mkfifo' creates FIFOs (also called "named pipes") with the specified
names.  Synopsis:

     mkfifo [OPTION] NAME...

   A "FIFO" is a special file type that permits independent processes
to communicate.  One process opens the FIFO file for writing, and
another for reading, after which data can flow as with the usual
anonymous pipe in shells or elsewhere.

   The program accepts the following option.  Also see *Note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the mode of created FIFOs to MODE, which is symbolic as in
     `chmod' and uses `a=rw' (read and write allowed for everyone) for
     the point of departure.  MODE should specify only file permission
     bits.  *Note File permissions::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: mknod invocation,  Next: readlink invocation,  Prev: mkfifo invocation,  Up: Special file types

12.5 `mknod': Make block or character special files
===================================================

`mknod' creates a FIFO, character special file, or block special file
with the specified name.  Synopsis:

     mknod [OPTION]... NAME TYPE [MAJOR MINOR]

   Unlike the phrase "special file type" above, the term "special file"
has a technical meaning on Unix: something that can generate or receive
data.  Usually this corresponds to a physical piece of hardware, e.g.,
a printer or a disk.  (These files are typically created at
system-configuration time.)  The `mknod' command is what creates files
of this type.  Such devices can be read either a character at a time or
a "block" (many characters) at a time, hence we say there are "block
special" files and "character special" files.

   The arguments after NAME specify the type of file to make:

`p'
     for a FIFO

`b'
     for a block special file

`c'
     for a character special file


   When making a block or character special file, the major and minor
device numbers must be given after the file type.  If a major or minor
device number begins with `0x' or `0X', it is interpreted as
hexadecimal; otherwise, if it begins with `0', as octal; otherwise, as
decimal.

   The program accepts the following option.  Also see *Note Common
options::.

`-m MODE'
`--mode=MODE'
     Set the mode of created files to MODE, which is symbolic as in
     `chmod' and uses `a=rw' as the point of departure.  MODE should
     specify only file permission bits.  *Note File permissions::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: readlink invocation,  Next: rmdir invocation,  Prev: mknod invocation,  Up: Special file types

12.6 `readlink': Print the referent of a symbolic link
======================================================

`readlink' may work in one of two supported modes:

`Readlink mode'
     `readlink' outputs the value of the given symbolic link.  If
     `readlink' is invoked with an argument other than the name of a
     symbolic link, it produces no output and exits with a nonzero exit
     code.

`Canonicalize mode'
     `readlink' outputs the absolute name of the given file which
     contains no `.', `..' components nor any repeated separators (`/')
     or symbolic links.


     readlink [OPTION] FILE

   By default, `readlink' operates in readlink mode.

   The program accepts the following options.  Also see *Note Common
options::.

`-f'
`--canonicalize'
     Activate canonicalize mode.  If any component of the file name
     except the last one is missing or unavailable, `readlink' produces
     no output and exits with a nonzero exit code.

`-e'
`--canonicalize-existing'
     Activate canonicalize mode.  If any component is missing or
     unavailable, `readlink' produces no output and exits with a
     nonzero exit code.

`-m'
`--canonicalize-missing'
     Activate canonicalize mode.  If any component is missing or
     unavailable, `readlink' treats it as a directory.

`-n'
`--no-newline'
     Do not output the trailing newline.

`-s'
`-q'
`--silent'
`--quiet'
     Suppress most error messages.

`-v'
`--verbose'
     Report error messages.


   The `readlink' utility first appeared in OpenBSD 2.1.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: rmdir invocation,  Next: unlink invocation,  Prev: readlink invocation,  Up: Special file types

12.7 `rmdir': Remove empty directories
======================================

`rmdir' removes empty directories.  Synopsis:

     rmdir [OPTION]... DIRECTORY...

   If any DIRECTORY argument does not refer to an existing empty
directory, it is an error.

   The program accepts the following option.  Also see *Note Common
options::.

`--ignore-fail-on-non-empty'
     Ignore each failure to remove a directory that is solely because
     the directory is non-empty.

`-p'
`--parents'
     Remove DIRECTORY, then try to remove each component of DIRECTORY.
     So, for example, `rmdir -p a/b/c' is similar to `rmdir a/b/c a/b
     a'.  As such, it fails if any of those directories turns out not
     to be empty.  Use the `--ignore-fail-on-non-empty' option to make
     it so such a failure does not evoke a diagnostic and does not
     cause `rmdir' to exit unsuccessfully.

`-v'
`--verbose'
     Give a diagnostic for each successful removal.  DIRECTORY is
     removed.


   *Note rm invocation::, for how to remove non-empty directories
(recursively).

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: unlink invocation,  Prev: rmdir invocation,  Up: Special file types

12.8 `unlink': Remove files via the unlink syscall
==================================================

`unlink' deletes a single specified file name.  It is a minimalist
interface to the system-provided `unlink' function.  *Note Deleting
Files: (libc)Deleting Files.  Synopsis: It avoids the bells and
whistles of the more commonly-used `rm' command (*note rm invocation::).

     unlink FILENAME

   On some systems `unlink' can be used to delete the name of a
directory.  On others, it can be used that way only by a privileged
user.  In the GNU system `unlink' can never delete the name of a
directory.

   The `unlink' command honors the `--help' and `--version' options.
To remove a file whose name begins with `-', prefix the name with `./',
e.g., `unlink ./--help'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Changing file attributes,  Next: Disk usage,  Prev: Special file types,  Up: Top

13 Changing file attributes
***************************

A file is not merely its contents, a name, and a file type (*note
Special file types::).  A file also has an owner (a user ID), a group
(a group ID), permissions (what the owner can do with the file, what
people in the group can do, and what everyone else can do), various
timestamps, and other information.  Collectively, we call these a file's
"attributes".

   These commands change file attributes.

* Menu:

* chgrp invocation::            Change file groups.
* chmod invocation::            Change access permissions.
* chown invocation::            Change file owners and groups.
* touch invocation::            Change file timestamps.


File: coreutils.info,  Node: chown invocation,  Next: touch invocation,  Prev: chmod invocation,  Up: Changing file attributes

13.1 `chown': Change file owner and group
=========================================

`chown' changes the user and/or group ownership of each given FILE to
NEW-OWNER or to the user and group of an existing reference file.
Synopsis:

     chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE...

   If used, NEW-OWNER specifies the new owner and/or group as follows
(with no embedded white space):

     [OWNER] [ : [GROUP] ]

   Specifically:

OWNER
     If only an OWNER (a user name or numeric user ID) is given, that
     user is made the owner of each given file, and the files' group is
     not changed.

OWNER`:'GROUP
     If the OWNER is followed by a colon and a GROUP (a group name or
     numeric group ID), with no spaces between them, the group
     ownership of the files is changed as well (to GROUP).

OWNER`:'
     If a colon but no group name follows OWNER, that user is made the
     owner of the files and the group of the files is changed to
     OWNER's login group.

`:'GROUP
     If the colon and following GROUP are given, but the owner is
     omitted, only the group of the files is changed; in this case,
     `chown' performs the same function as `chgrp'.

`:'
     If only a colon is given, or if NEW-OWNER is empty, neither the
     owner nor the group is changed.


   If OWNER or GROUP is intended to represent a numeric user or group
ID, then you may specify it with a leading `+'.  *Note Disambiguating
names and IDs::.

   Some older scripts may still use `.' in place of the `:' separator.
POSIX 1003.1-2001 (*note Standards conformance::) does not require
support for that, but for backward compatibility GNU `chown' supports
`.' so long as no ambiguity results.  New scripts should avoid the use
of `.' because it is not portable, and because it has undesirable
results if the entire OWNER`.'GROUP happens to identify a user whose
name contains `.'.

   The `chown' command sometimes clears the set-user-ID or set-group-ID
permission bits.  This behavior depends on the policy and functionality
of the underlying `chown' system call, which may make system-dependent
file mode modifications outside the control of the `chown' command.
For example, the `chown' command might not affect those bits when
invoked by a user with appropriate privileges, or when the bits signify
some function other than executable permission (e.g., mandatory
locking).  When in doubt, check the underlying system behavior.

   The program accepts the following options.  Also see *Note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose ownership
     actually changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose ownership cannot be
     changed.

`--from=OLD-OWNER'
     Change a FILE's ownership only if it has current attributes
     specified by OLD-OWNER.  OLD-OWNER has the same form as NEW-OWNER
     described above.  This option is useful primarily from a security
     standpoint in that it narrows considerably the window of potential
     abuse.  For example, to reflect a user ID numbering change for one
     user's files without an option like this, `root' might run

          find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER

     But that is dangerous because the interval between when the `find'
     tests the existing file's owner and when the `chown' is actually
     run may be quite large.  One way to narrow the gap would be to
     invoke chown for each file as it is found:

          find / -owner OLDUSER -exec chown -h NEWUSER {} \;

     But that is very slow if there are many affected files.  With this
     option, it is safer (the gap is narrower still) though still not
     perfect:

          chown -h -R --from=OLDUSER NEWUSER /

`--dereference'
     Do not act on symbolic links themselves but rather on what they
     point to.  This is the default.

`-h'
`--no-dereference'
     Act on symbolic links themselves instead of what they point to.
     This mode relies on the `lchown' system call.  On systems that do
     not provide the `lchown' system call, `chown' fails when a file
     specified on the command line is a symbolic link.  By default, no
     diagnostic is issued for symbolic links encountered during a
     recursive traversal, but see `--verbose'.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`--reference=REF_FILE'
     Change the user and group of each FILE to be the same as those of
     REF_FILE.  If REF_FILE is a symbolic link, do not use the user and
     group of the symbolic link, but rather those of the file it refers
     to.

`-v'
`--verbose'
     Output a diagnostic for every file processed.  If a symbolic link
     is encountered during a recursive traversal on a system without
     the `lchown' system call, and `--no-dereference' is in effect,
     then issue a diagnostic saying neither the symbolic link nor its
     referent is being changed.

`-R'
`--recursive'
     Recursively change ownership of directories and their contents.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.  *Note Traversing
     symlinks::.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.  *Note Traversing symlinks::.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.  *Note Traversing symlinks::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Change the owner of /u to "root".
     chown root /u

     # Likewise, but also change its group to "staff".
     chown root:staff /u

     # Change the owner of /u and subfiles to "root".
     chown -hR root /u


File: coreutils.info,  Node: chgrp invocation,  Next: chmod invocation,  Up: Changing file attributes

13.2 `chgrp': Change group ownership
====================================

`chgrp' changes the group ownership of each given FILE to GROUP (which
can be either a group name or a numeric group ID) or to the group of an
existing reference file.  Synopsis:

     chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE...

   If GROUP is intended to represent a numeric group ID, then you may
specify it with a leading `+'.  *Note Disambiguating names and IDs::.

   The program accepts the following options.  Also see *Note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose group actually
     changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose group cannot be
     changed.

`--dereference'
     Do not act on symbolic links themselves but rather on what they
     point to.  This is the default.

`-h'
`--no-dereference'
     Act on symbolic links themselves instead of what they point to.
     This mode relies on the `lchown' system call.  On systems that do
     not provide the `lchown' system call, `chgrp' fails when a file
     specified on the command line is a symbolic link.  By default, no
     diagnostic is issued for symbolic links encountered during a
     recursive traversal, but see `--verbose'.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`--reference=REF_FILE'
     Change the group of each FILE to be the same as that of REF_FILE.
     If REF_FILE is a symbolic link, do not use the group of the
     symbolic link, but rather that of the file it refers to.

`-v'
`--verbose'
     Output a diagnostic for every file processed.  If a symbolic link
     is encountered during a recursive traversal on a system without
     the `lchown' system call, and `--no-dereference' is in effect,
     then issue a diagnostic saying neither the symbolic link nor its
     referent is being changed.

`-R'
`--recursive'
     Recursively change the group ownership of directories and their
     contents.

`-H'
     If `--recursive' (`-R') is specified and a command line argument
     is a symbolic link to a directory, traverse it.  *Note Traversing
     symlinks::.

`-L'
     In a recursive traversal, traverse every symbolic link to a
     directory that is encountered.  *Note Traversing symlinks::.

`-P'
     Do not traverse any symbolic links.  This is the default if none
     of `-H', `-L', or `-P' is specified.  *Note Traversing symlinks::.


   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Change the group of /u to "staff".
     chgrp staff /u

     # Change the group of /u and subfiles to "staff".
     chgrp -hR staff /u


File: coreutils.info,  Node: chmod invocation,  Next: chown invocation,  Prev: chgrp invocation,  Up: Changing file attributes

13.3 `chmod': Change access permissions
=======================================

`chmod' changes the access permissions of the named files.  Synopsis:

     chmod [OPTION]... {MODE | --reference=REF_FILE} FILE...

   `chmod' never changes the permissions of symbolic links, since the
`chmod' system call cannot change their permissions.  This is not a
problem since the permissions of symbolic links are never used.
However, for each symbolic link listed on the command line, `chmod'
changes the permissions of the pointed-to file.  In contrast, `chmod'
ignores symbolic links encountered during recursive directory
traversals.

   A successful use of `chmod' clears the set-group-ID bit of a regular
file if the file's group ID does not match the user's effective group
ID or one of the user's supplementary group IDs, unless the user has
appropriate privileges.  Additional restrictions may cause the
set-user-ID and set-group-ID bits of MODE or REF_FILE to be ignored.
This behavior depends on the policy and functionality of the underlying
`chmod' system call.  When in doubt, check the underlying system
behavior.

   If used, MODE specifies the new file mode bits.  For details, see
the section on *Note File permissions::.  If you really want MODE to
have a leading `-', you should use `--' first, e.g., `chmod -- -w
file'.  Typically, though, `chmod a-w file' is preferable, and `chmod -w
file' (without the `--') complains if it behaves differently from what
`chmod a-w file' would do.

   The program accepts the following options.  Also see *Note Common
options::.

`-c'
`--changes'
     Verbosely describe the action for each FILE whose permissions
     actually changes.

`-f'
`--silent'
`--quiet'
     Do not print error messages about files whose permissions cannot be
     changed.

`--preserve-root'
     Fail upon any attempt to recursively change the root directory,
     `/'.  Without `--recursive', this option has no effect.  *Note
     Treating / specially::.

`--no-preserve-root'
     Cancel the effect of any preceding `--preserve-root' option.
     *Note Treating / specially::.

`-v'
`--verbose'
     Verbosely describe the action or non-action taken for every FILE.

`--reference=REF_FILE'
     Change the mode of each FILE to be the same as that of REF_FILE.
     *Note File permissions::.  If REF_FILE is a symbolic link, do not
     use the mode of the symbolic link, but rather that of the file it
     refers to.

`-R'
`--recursive'
     Recursively change permissions of directories and their contents.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: touch invocation,  Prev: chown invocation,  Up: Changing file attributes

13.4 `touch': Change file timestamps
====================================

`touch' changes the access and/or modification times of the specified
files.  Synopsis:

     touch [OPTION]... FILE...

   Any FILE that does not exist is created empty.

   A FILE of `-' causes `touch' to change the times of the file
associated with standard output.

   If changing both the access and modification times to the current
time, `touch' can change the timestamps for files that the user running
it does not own but has write permission for.  Otherwise, the user must
own the files.

   Although `touch' provides options for changing two of the times--the
times of last access and modification--of a file, there is actually a
third one as well: the inode change time.  This is often referred to as
a file's `ctime'.  The inode change time represents the time when the
file's meta-information last changed.  One common example of this is
when the permissions of a file change.  Changing the permissions
doesn't access the file, so the atime doesn't change, nor does it
modify the file, so the mtime doesn't change.  Yet, something about the
file itself has changed, and this must be noted somewhere.  This is the
job of the ctime field.  This is necessary, so that, for example, a
backup program can make a fresh copy of the file, including the new
permissions value.  Another operation that modifies a file's ctime
without affecting the others is renaming.  In any case, it is not
possible, in normal operations, for a user to change the ctime field to
a user-specified value.

   Time stamps assume the time zone rules specified by the `TZ'
environment variable, or by the system default rules if `TZ' is not
set.  *Note Specifying the Time Zone with `TZ': (libc)TZ Variable.  You
can avoid ambiguities during daylight saving transitions by using UTC
time stamps.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--time=atime'
`--time=access'
`--time=use'
     Change the access time only.

`-c'
`--no-create'
     Do not create files that do not exist.

`-d'
`--date=TIME'
     Use TIME instead of the current time.  It can contain month names,
     time zones, `am' and `pm', `yesterday', etc.  For example,
     `--date="2004-02-27 14:19:13.489392193 +0530"' specifies the
     instant of time that is 489,392,193 nanoseconds after February 27,
     2004 at 2:19:13 PM in a time zone that is 5 hours and 30 minutes
     east of UTC.  *Note Date input formats::.  File systems that do
     not support high-resolution time stamps silently ignore any excess
     precision here.

`-f'
     Ignored; for compatibility with BSD versions of `touch'.

`-m'
`--time=mtime'
`--time=modify'
     Change the modification time only.

`-r FILE'
`--reference=FILE'
     Use the times of the reference FILE instead of the current time.
     If this option is combined with the `--date=TIME' (`-d TIME')
     option, the reference FILE's time is the origin for any relative
     TIMEs given, but is otherwise ignored.  For example, `-r foo -d
     '-5 seconds'' specifies a time stamp equal to five seconds before
     the corresponding time stamp for `foo'.

`-t [[CC]YY]MMDDHHMM[.SS]'
     Use the argument (optional four-digit or two-digit years, months,
     days, hours, minutes, optional seconds) instead of the current
     time.  If the year is specified with only two digits, then CC is
     20 for years in the range 0 ... 68, and 19 for years in 69 ... 99.
     If no digits of the year are specified, the argument is
     interpreted as a date in the current year.


   On older systems, `touch' supports an obsolete syntax, as follows.
If no timestamp is given with any of the `-d', `-r', or `-t' options,
and if there are two or more FILEs and the first FILE is of the form
`MMDDHHMM[YY]' and this would be a valid argument to the `-t' option
(if the YY, if any, were moved to the front), and if the represented
year is in the range 1969-1999, that argument is interpreted as the time
for the other files instead of as a file name.  This obsolete behavior
can be enabled or disabled with the `_POSIX2_VERSION' environment
variable (*note Standards conformance::), but portable scripts should
avoid commands whose behavior depends on this variable.  For example,
use `touch ./12312359 main.c' or `touch -t 12312359 main.c' rather than
the ambiguous `touch 12312359 main.c'.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Disk usage,  Next: Printing text,  Prev: Changing file attributes,  Up: Top

14 Disk usage
*************

No disk can hold an infinite amount of data.  These commands report how
much disk storage is in use or available, report other file and file
status information, and write buffers to disk.

* Menu:

* df invocation::               Report file system disk space usage.
* du invocation::               Estimate file space usage.
* stat invocation::             Report file or file system status.
* sync invocation::             Synchronize memory and disk.


File: coreutils.info,  Node: df invocation,  Next: du invocation,  Up: Disk usage

14.1 `df': Report file system disk space usage
==============================================

`df' reports the amount of disk space used and available on file
systems.  Synopsis:

     df [OPTION]... [FILE]...

   With no arguments, `df' reports the space used and available on all
currently mounted file systems (of all types).  Otherwise, `df' reports
on the file system containing each argument FILE.

   Normally the disk space is printed in units of 1024 bytes, but this
can be overridden (*note Block size::).  Non-integer quantities are
rounded up to the next higher unit.

   If an argument FILE is a disk device file containing a mounted file
system, `df' shows the space available on that file system rather than
on the file system containing the device node (i.e., the root file
system).  GNU `df' does not attempt to determine the disk usage on
unmounted file systems, because on most kinds of systems doing so
requires extremely nonportable intimate knowledge of file system
structures.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--all'
     Include in the listing dummy file systems, which are omitted by
     default.  Such file systems are typically special-purpose
     pseudo-file-systems, such as automounter entries.

`-B SIZE'
`--block-size=SIZE'
     Scale sizes by SIZE before printing them (*note Block size::).
     For example, `-BG' prints sizes in units of 1,073,741,824 bytes.

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     Use the `--si' option if you prefer powers of 1000.

`-H'
     Equivalent to `--si'.

`-i'
`--inodes'
     List inode usage information instead of block usage.  An inode
     (short for index node) contains information about a file such as
     its owner, permissions, timestamps, and location on the disk.

`-k'
     Print sizes in 1024-byte blocks, overriding the default block size
     (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-l'
`--local'
     Limit the listing to local file systems.  By default, remote file
     systems are also listed.

`--no-sync'
     Do not invoke the `sync' system call before getting any usage data.
     This may make `df' run significantly faster on systems with many
     disks, but on some systems (notably SunOS) the results may be
     slightly out of date.  This is the default.

`-P'
`--portability'
     Use the POSIX output format.  This is like the default format
     except for the following:

       1. The information about each file system is always printed on
          exactly one line; a mount device is never put on a line by
          itself.  This means that if the mount device name is more
          than 20 characters long (e.g., for some network mounts), the
          columns are misaligned.

       2. The labels in the header output line are changed to conform
          to POSIX.

       3. The default block size and output format are unaffected by the
          `DF_BLOCK_SIZE', `BLOCK_SIZE' and `BLOCKSIZE' environment
          variables.  However, the default block size is still affected
          by `POSIXLY_CORRECT': it is 512 if `POSIXLY_CORRECT' is set,
          1024 otherwise.  *Note Block size::.

`--si'
     Append an SI-style abbreviation to each size, such as `M' for
     megabytes.  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  This option is equivalent to `--block-size=si'.
     Use the `-h' or `--human-readable' option if you prefer powers of
     1024.

`--sync'
     Invoke the `sync' system call before getting any usage data.  On
     some systems (notably SunOS), doing this yields more up to date
     results, but in general this option makes `df' much slower,
     especially when there are many or very busy file systems.

`-t FSTYPE'
`--type=FSTYPE'
     Limit the listing to file systems of type FSTYPE.  Multiple file
     system types can be specified by giving multiple `-t' options.  By
     default, nothing is omitted.

`-T'
`--print-type'
     Print each file system's type.  The types printed here are the
     same ones you can include or exclude with `-t' and `-x'.  The
     particular types printed are whatever is supported by the system.
     Here are some of the common names (this list is certainly not
     exhaustive):

    `nfs'
          An NFS file system, i.e., one mounted over a network from
          another machine.  This is the one type name which seems to be
          used uniformly by all systems.

    `4.2, ufs, efs...'
          A file system on a locally-mounted hard disk.  (The system
          might even support more than one type here; Linux does.)

    `hsfs, cdfs'
          A file system on a CD-ROM drive.  HP-UX uses `cdfs', most
          other systems use `hsfs' (`hs' for "High Sierra").

    `pcfs'
          An MS-DOS file system, usually on a diskette.


`-x FSTYPE'
`--exclude-type=FSTYPE'
     Limit the listing to file systems not of type FSTYPE.  Multiple
     file system types can be eliminated by giving multiple `-x'
     options.  By default, no file system types are omitted.

`-v'
     Ignored; for compatibility with System V versions of `df'.


   An exit status of zero indicates success, and a nonzero value
indicates failure.  Failure includes the case where no output is
generated, so you can inspect the exit status of a command like `df -t
ext3 -t reiserfs DIR' to test whether DIR is on a file system of type
`ext3' or `reiserfs'.


File: coreutils.info,  Node: du invocation,  Next: stat invocation,  Prev: df invocation,  Up: Disk usage

14.2 `du': Estimate file space usage
====================================

`du' reports the amount of disk space used by the specified files and
for each subdirectory (of directory arguments).  Synopsis:

     du [OPTION]... [FILE]...

   With no arguments, `du' reports the disk space for the current
directory.  Normally the disk space is printed in units of 1024 bytes,
but this can be overridden (*note Block size::).  Non-integer
quantities are rounded up to the next higher unit.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--all'
     Show counts for all files, not just directories.

`--apparent-size'
     Print apparent sizes, rather than disk usage.  The apparent size
     of a file is the number of bytes reported by `wc -c' on regular
     files, or more generally, `ls -l --block-size=1' or `stat
     --format=%s'.  For example, a file containing the word `zoo' with
     no newline would, of course, have an apparent size of 3.  Such a
     small file may require anywhere from 0 to 16 KiB or more of disk
     space, depending on the type and configuration of the file system
     on which the file resides.  However, a sparse file created with
     this command:

          dd bs=1 seek=2GiB if=/dev/null of=big

     has an apparent size of 2 GiB, yet on most modern systems, it
     actually uses almost no disk space.

`-b'
`--bytes'
     Equivalent to `--apparent-size --block-size=1'.

`-B SIZE'
`--block-size=SIZE'
     Scale sizes by SIZE before printing them (*note Block size::).
     For example, `-BG' prints sizes in units of 1,073,741,824 bytes.

`-c'
`--total'
     Print a grand total of all arguments after all arguments have been
     processed.  This can be used to find out the total disk usage of a
     given set of files or directories.

`-D'
`--dereference-args'
     Dereference symbolic links that are command line arguments.  Does
     not affect other symbolic links.  This is helpful for finding out
     the disk usage of directories, such as `/usr/tmp', which are often
     symbolic links.

`--files0-from=FILE'
     Rather than processing files named on the command line, process
     those named in file FILE; each name is terminated by a null byte.
     This is useful with the `--total' (`-c') option when the list of
     file names is so long that it may exceed a command line length
     limitation.  In such cases, running `du' via `xargs' is undesirable
     because it splits the list into pieces and makes `du' print a
     total for each sublist rather than for the entire list.  One way
     to produce a list of null-byte-terminated file names is with GNU
     `find', using its `-print0' predicate.  Do not specify any FILE on
     the command line when using this option.

`-h'
`--human-readable'
     Append a size letter to each size, such as `M' for mebibytes.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     Use the `--si' option if you prefer powers of 1000.

`-H'
     Currently, `-H' is the same as `--si', except that `-H' evokes a
     warning.  This option will be changed to be equivalent to
     `--dereference-args' (`-D').

`-k'
     Print sizes in 1024-byte blocks, overriding the default block size
     (*note Block size::).  This option is equivalent to
     `--block-size=1K'.

`-l'
`--count-links'
     Count the size of all files, even if they have appeared already
     (as a hard link).

`-L'
`--dereference'
     Dereference symbolic links (show the disk space used by the file
     or directory that the link points to instead of the space used by
     the link).

`-m'
     Print sizes in 1,048,576-byte blocks, overriding the default block
     size (*note Block size::).  This option is equivalent to
     `--block-size=1M'.

`-P'
`--no-dereference'
     For each symbolic links encountered by `du', consider the disk
     space used by the symbolic link.

`--max-depth=DEPTH'
     Show the total for each directory (and file if -all) that is at
     most MAX_DEPTH levels down from the root of the hierarchy.  The
     root is at level 0, so `du --max-depth=0' is equivalent to `du -s'.

`-0'
`--null'
     Output a null byte at the end of each line, rather than a newline.
     This option enables other programs to parse the output of `du'
     even when that output would contain file names with embedded
     newlines.

`--si'
     Append an SI-style abbreviation to each size, such as `MB' for
     megabytes.  Powers of 1000 are used, not 1024; `MB' stands for
     1,000,000 bytes.  Use the `-h' or `--human-readable' option if you
     prefer powers of 1024.

`-s'
`--summarize'
     Display only a total for each argument.

`-S'
`--separate-dirs'
     Report the size of each directory separately, not including the
     sizes of subdirectories.

`--time'
     Show time of the most recent modification of any file in the
     directory, or any of its subdirectories.

`--time=ctime'
`--time=status'
`--time=use'
     Show the most recent status change time (the `ctime' in the inode)
     of any file in the directory, instead of the modification time.

`--time=atime'
`--time=access'
     Show the most recent access time (the `atime' in the inode) of any
     file in the directory, instead of the modification time.

`--time-style=STYLE'
     List timestamps in style STYLE.  This option has an effect only if
     the `--time' option is also specified.  The STYLE should be one of
     the following:

    `+FORMAT'
          List timestamps using FORMAT, where FORMAT is interpreted
          like the format argument of `date' (*note date invocation::).
          For example, `--time-style="+%Y-%m-%d %H:%M:%S"' causes `du'
          to list timestamps like `2002-03-30 23:45:56'.  As with
          `date', FORMAT's interpretation is affected by the `LC_TIME'
          locale category.

    `full-iso'
          List timestamps in full using ISO 8601 date, time, and time
          zone format with nanosecond precision, e.g., `2002-03-30
          23:45:56.477817180 -0700'.  This style is equivalent to
          `+%Y-%m-%d %H:%M:%S.%N %z'.

    `long-iso'
          List ISO 8601 date and time in minutes, e.g., `2002-03-30
          23:45'.  These timestamps are shorter than `full-iso'
          timestamps, and are usually good enough for everyday work.
          This style is equivalent to `+%Y-%m-%d %H:%M'.

    `iso'
          List ISO 8601 dates for timestamps, e.g., `2002-03-30'.  This
          style is equivalent to `+%Y-%m-%d'.

     You can specify the default value of the `--time-style' option
     with the environment variable `TIME_STYLE'; if `TIME_STYLE' is not
     set the default style is `long-iso'.  For compatibility with `ls',
     if `TIME_STYLE' begins with `+' and contains a newline, the
     newline and any later characters are ignored; if `TIME_STYLE'
     begins with `posix-' the `posix-' is ignored; and if `TIME_STYLE'
     is `locale' it is ignored.

`-x'
`--one-file-system'
     Skip directories that are on different file systems from the one
     that the argument being processed is on.

`--exclude=PATTERN'
     When recursing, skip subdirectories or files matching PATTERN.
     For example, `du --exclude='*.o'' excludes files whose names end
     in `.o'.

`-X FILE'
`--exclude-from=FILE'
     Like `--exclude', except take the patterns to exclude from FILE,
     one per line.  If FILE is `-', take the patterns from standard
     input.


   On BSD systems, `du' reports sizes that are half the correct values
for files that are NFS-mounted from HP-UX systems.  On HP-UX systems,
it reports sizes that are twice the correct values for files that are
NFS-mounted from BSD systems.  This is due to a flaw in HP-UX; it also
affects the HP-UX `du' program.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: stat invocation,  Next: sync invocation,  Prev: du invocation,  Up: Disk usage

14.3 `stat': Report file or file system status
==============================================

`stat' displays information about the specified file(s).  Synopsis:

     stat [OPTION]... [FILE]...

   With no option, `stat' reports all information about the given files.
But it also can be used to report the information of the file systems
the given files are located on.  If the files are links, `stat' can
also give information about the files the links point to.

`-L'
`--dereference'
     Change how `stat' treats symbolic links.  With this option, `stat'
     acts on the file referenced by each symbolic link argument.
     Without it, `stat' acts on any symbolic link argument directly.

`-f'
`--file-system'
     Report information about the file systems where the given files
     are located instead of information about the files themselves.

`-c'
`--format=FORMAT'
     Use FORMAT rather than the default format.  FORMAT is
     automatically newline-terminated, so running a command like the
     following with two or more FILE operands produces a line of output
     for each operand:
          $ stat --format=%d:%i / /usr
          2050:2
          2057:2

`--printf=FORMAT'
     Use FORMAT rather than the default format.  Like `--format', but
     interpret backslash escapes, and do not output a mandatory
     trailing newline.  If you want a newline, include `\n' in the
     FORMAT.  Here's how you would use `--printf' to print the device
     and inode numbers of `/' and `/usr':
          $ stat --printf='%d:%i\n' / /usr
          2050:2
          2057:2

`-t'
`--terse'
     Print the information in terse form, suitable for parsing by other
     programs.

     The valid format sequences for files are:

        * %a - Access rights in octal

        * %A - Access rights in human readable form

        * %b - Number of blocks allocated (see `%B')

        * %B - The size in bytes of each block reported by `%b'

        * %d - Device number in decimal

        * %D - Device number in hex

        * %f - Raw mode in hex

        * %F - File type

        * %g - Group ID of owner

        * %G - Group name of owner

        * %h - Number of hard links

        * %i - Inode number

        * %n - File name

        * %N - Quoted file name with dereference if symbolic link

        * %o - I/O block size

        * %s - Total size, in bytes

        * %t - Major device type in hex

        * %T - Minor device type in hex

        * %u - User ID of owner

        * %U - User name of owner

        * %x - Time of last access

        * %X - Time of last access as seconds since Epoch

        * %y - Time of last modification

        * %Y - Time of last modification as seconds since Epoch

        * %z - Time of last change

        * %Z - Time of last change as seconds since Epoch

     The valid format sequences for file systems are:

        * %a - Free blocks available to non-super-user

        * %b - Total data blocks in file system

        * %c - Total file nodes in file system

        * %d - Free file nodes in file system

        * %f - Free blocks in file system

        * %i - File System ID in hex

        * %l - Maximum length of file names

        * %n - File name

        * %s - Block size (for faster transfers)

        * %S - Fundamental block size (for block counts)

        * %t - Type in hex

        * %T - Type in human readable form

     Time stamps are listed according to the time zone rules specified
     by the `TZ' environment variable, or by the system default rules if
     `TZ' is not set.  *Note Specifying the Time Zone with `TZ':
     (libc)TZ Variable.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: sync invocation,  Prev: stat invocation,  Up: Disk usage

14.4 `sync': Synchronize data on disk with memory
=================================================

`sync' writes any data buffered in memory out to disk.  This can
include (but is not limited to) modified superblocks, modified inodes,
and delayed reads and writes.  This must be implemented by the kernel;
The `sync' program does nothing but exercise the `sync' system call.

   The kernel keeps data in memory to avoid doing (relatively slow) disk
reads and writes.  This improves performance, but if the computer
crashes, data may be lost or the file system corrupted as a result.
The `sync' command ensures everything in memory is written to disk.

   Any arguments are ignored, except for a lone `--help' or `--version'
(*note Common options::).

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Printing text,  Next: Conditions,  Prev: Disk usage,  Up: Top

15 Printing text
****************

This section describes commands that display text strings.

* Menu:

* echo invocation::             Print a line of text.
* printf invocation::           Format and print data.
* yes invocation::              Print a string until interrupted.


File: coreutils.info,  Node: echo invocation,  Next: printf invocation,  Up: Printing text

15.1 `echo': Print a line of text
=================================

`echo' writes each given STRING to standard output, with a space
between each and a newline after the last one.  Synopsis:

     echo [OPTION]... [STRING]...

   The program accepts the following options.  Also see *Note Common
options::.  Options must precede operands, and the normally-special
argument `--' has no special meaning and is treated like any other
STRING.

`-n'
     Do not output the trailing newline.

`-e'
     Enable interpretation of the following backslash-escaped
     characters in each STRING:

    `\a'
          alert (bell)

    `\b'
          backspace

    `\c'
          suppress trailing newline

    `\f'
          form feed

    `\n'
          new line

    `\r'
          carriage return

    `\t'
          horizontal tab

    `\v'
          vertical tab

    `\\'
          backslash

    `\0NNN'
          the eight-bit value that is the octal number NNN (zero to
          three octal digits)

    `\NNN'
          the eight-bit value that is the octal number NNN (one to
          three octal digits)

    `\xHH'
          the eight-bit value that is the hexadecimal number HH (one or
          two hexadecimal digits)

`-E'
     Disable interpretation of backslash escapes in each STRING.  This
     is the default.  If `-e' and `-E' are both specified, the last one
     given takes effect.


   If the `POSIXLY_CORRECT' environment variable is set, then when
`echo''s first argument is not `-n' it outputs option-like arguments
instead of treating them as options.  For example, `echo -ne hello'
outputs `-ne hello' instead of plain `hello'.

   POSIX does not require support for any options, and says that the
behavior of `echo' is implementation-defined if any STRING contains a
backslash or if the first argument is `-n'.  Portable programs can use
the `printf' command if they need to omit trailing newlines or output
control characters or backslashes.  *Note printf invocation::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: printf invocation,  Next: yes invocation,  Prev: echo invocation,  Up: Printing text

15.2 `printf': Format and print data
====================================

`printf' does formatted printing of text.  Synopsis:

     printf FORMAT [ARGUMENT]...

   `printf' prints the FORMAT string, interpreting `%' directives and
`\' escapes to format numeric and string arguments in a way that is
mostly similar to the C `printf' function.  The differences are as
follows:

   * The FORMAT argument is reused as necessary to convert all the
     given ARGUMENTs.  For example, the command `printf %s a b' outputs
     `ab'.

   * Missing ARGUMENTs are treated as null strings or as zeros,
     depending on whether the context expects a string or a number.  For
     example, the command `printf %sx%d' prints `x0'.

   * An additional escape, `\c', causes `printf' to produce no further
     output.  For example, the command `printf 'A%sC\cD%sF' B E' prints
     `ABC'.

   * The hexadecimal escape sequence `\xHH' has at most two digits, as
     opposed to C where it can have an unlimited number of digits.  For
     example, the command `printf '\x07e'' prints two bytes, whereas
     the C statement `printf ("\x07e")' prints just one.

   * `printf' has an additional directive, `%b', which prints its
     argument string with `\' escapes interpreted in the same way as in
     the FORMAT string, except that octal escapes are of the form
     `\0OOO' where OOO is 0 to 3 octal digits.  If a precision is also
     given, it limits the number of bytes printed from the converted
     string.

   * Numeric arguments must be single C constants, possibly with leading
     `+' or `-'.  For example, `printf %.4d -3' outputs `-0003'.

   * If the leading character of a numeric argument is `"' or `'' then
     its value is the numeric value of the immediately following
     character.  Any remaining characters are silently ignored if the
     `POSIXLY_CORRECT' environment variable is set; otherwise, a
     warning is printed.  For example, `printf "%d" "'a"' outputs `97'
     on hosts that use the ASCII character set, since `a' has the
     numeric value 97 in ASCII.


   A floating-point argument must use a period before any fractional
digits, but is printed according to the `LC_NUMERIC' category of the
current locale.  For example, in a locale whose radix character is a
comma, the command `printf %g 3.14' outputs `3,14' whereas the command
`printf %g 3,14' is an error.

   `printf' interprets `\OOO' in FORMAT as an octal number (if OOO is 1
to 3 octal digits) specifying a character to print, and `\xHH' as a
hexadecimal number (if HH is 1 to 2 hex digits) specifying a character
to print.

   `printf' interprets two character syntaxes introduced in ISO C 99:
`\u' for 16-bit Unicode (ISO/IEC 10646) characters, specified as four
hexadecimal digits HHHH, and `\U' for 32-bit Unicode characters,
specified as eight hexadecimal digits HHHHHHHH.  `printf' outputs the
Unicode characters according to the `LC_CTYPE' locale.

   The processing of `\u' and `\U' requires a full-featured `iconv'
facility.  It is activated on systems with glibc 2.2 (or newer), or
when `libiconv' is installed prior to this package.  Otherwise `\u' and
`\U' will print as-is.

   The only options are a lone `--help' or `--version'.  *Note Common
options::.  Options must precede operands.

   The Unicode character syntaxes are useful for writing strings in a
locale independent way.  For example, a string containing the Euro
currency symbol

     $ /usr/local/bin/printf '\u20AC 14.95'

will be output correctly in all locales supporting the Euro symbol
(ISO-8859-15, UTF-8, and others).  Similarly, a Chinese string

     $ /usr/local/bin/printf '\u4e2d\u6587'

will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8,
etc).

   Note that in these examples, the full name of `printf' has been
given, to distinguish it from the GNU `bash' built-in function `printf'.

   For larger strings, you don't need to look up the hexadecimal code
values of each character one by one.  ASCII characters mixed with \u
escape sequences is also known as the JAVA source file encoding.  You
can use GNU recode 3.5c (or newer) to convert strings to this encoding.
Here is how to convert a piece of text into a shell script which will
output this text in a locale-independent way:

     $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
         '\u4e2d\u6587\n' > sample.txt
     $ recode BIG5..JAVA < sample.txt \
         | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
         > sample.sh

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: yes invocation,  Prev: printf invocation,  Up: Printing text

15.3 `yes': Print a string until interrupted
============================================

`yes' prints the command line arguments, separated by spaces and
followed by a newline, forever until it is killed.  If no arguments are
given, it prints `y' followed by a newline forever until killed.

   Upon a write error, `yes' exits with status `1'.

   The only options are a lone `--help' or `--version'.  To output an
argument that begins with `-', precede it with `--', e.g., `yes --
--help'.  *Note Common options::.


File: coreutils.info,  Node: Conditions,  Next: Redirection,  Prev: Printing text,  Up: Top

16 Conditions
*************

This section describes commands that are primarily useful for their exit
status, rather than their output.  Thus, they are often used as the
condition of shell `if' statements, or as the last command in a
pipeline.

* Menu:

* false invocation::            Do nothing, unsuccessfully.
* true invocation::             Do nothing, successfully.
* test invocation::             Check file types and compare values.
* expr invocation::             Evaluate expressions.


File: coreutils.info,  Node: false invocation,  Next: true invocation,  Up: Conditions

16.1 `false': Do nothing, unsuccessfully
========================================

`false' does nothing except return an exit status of 1, meaning
"failure".  It can be used as a place holder in shell scripts where an
unsuccessful command is needed.  In most modern shells, `false' is a
built-in command, so when you use `false' in a script, you're probably
using the built-in command, not the one documented here.

   `false' honors the `--help' and `--version' options.

   This version of `false' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.

   Note that `false' (unlike all other programs documented herein)
exits unsuccessfully, even when invoked with `--help' or `--version'.

   Portable programs should not assume that the exit status of `false'
is 1, as it is greater than 1 on some non-GNU hosts.


File: coreutils.info,  Node: true invocation,  Next: test invocation,  Prev: false invocation,  Up: Conditions

16.2 `true': Do nothing, successfully
=====================================

`true' does nothing except return an exit status of 0, meaning
"success".  It can be used as a place holder in shell scripts where a
successful command is needed, although the shell built-in command `:'
(colon) may do the same thing faster.  In most modern shells, `true' is
a built-in command, so when you use `true' in a script, you're probably
using the built-in command, not the one documented here.

   `true' honors the `--help' and `--version' options.

   Note, however, that it is possible to cause `true' to exit with
nonzero status: with the `--help' or `--version' option, and with
standard output already closed or redirected to a file that evokes an
I/O error.  For example, using a Bourne-compatible shell:

     $ ./true --version >&-
     ./true: write error: Bad file number
     $ ./true --version > /dev/full
     ./true: write error: No space left on device

   This version of `true' is implemented as a C program, and is thus
more secure and faster than a shell script implementation, and may
safely be used as a dummy shell for the purpose of disabling accounts.


File: coreutils.info,  Node: test invocation,  Next: expr invocation,  Prev: true invocation,  Up: Conditions

16.3 `test': Check file types and compare values
================================================

`test' returns a status of 0 (true) or 1 (false) depending on the
evaluation of the conditional expression EXPR.  Each part of the
expression must be a separate argument.

   `test' has file status checks, string operators, and numeric
comparison operators.

   `test' has an alternate form that uses opening and closing square
brackets instead a leading `test'.  For example, instead of `test -d
/', you can write `[ -d / ]'.  The square brackets must be separate
arguments; for example, `[-d /]' does not have the desired effect.
Since `test EXPR' and `[ EXPR ]' have the same meaning, only the former
form is discussed below.

   Synopses:

     test EXPRESSION
     test
     [ EXPRESSION ]
     [ ]
     [ OPTION

   Because most shells have a built-in `test' command, using an
unadorned `test' in a script or interactively may get you different
functionality than that described here.

   If EXPRESSION is omitted, `test' returns false.  If EXPRESSION is a
single argument, `test' returns false if the argument is null and true
otherwise.  The argument can be any string, including strings like
`-d', `-1', `--', `--help', and `--version' that most other programs
would treat as options.  To get help and version information, invoke
the commands `[ --help' and `[ --version', without the usual closing
brackets.  *Note Common options::.

   Exit status:

     0 if the expression is true,
     1 if the expression is false,
     2 if an error occurred.

* Menu:

* File type tests::             -[bcdfhLpSt]
* Access permission tests::     -[gkruwxOG]
* File characteristic tests::   -e -s -nt -ot -ef
* String tests::                -z -n = !=
* Numeric tests::               -eq -ne -lt -le -gt -ge
* Connectives for test::        ! -a -o


File: coreutils.info,  Node: File type tests,  Next: Access permission tests,  Up: test invocation

16.3.1 File type tests
----------------------

These options test for particular types of files.  (Everything's a file,
but not all files are the same!)

`-b FILE'
     True if FILE exists and is a block special device.

`-c FILE'
     True if FILE exists and is a character special device.

`-d FILE'
     True if FILE exists and is a directory.

`-f FILE'
     True if FILE exists and is a regular file.

`-h FILE'
`-L FILE'
     True if FILE exists and is a symbolic link.  Unlike all other
     file-related tests, this test does not dereference FILE if it is a
     symbolic link.

`-p FILE'
     True if FILE exists and is a named pipe.

`-S FILE'
     True if FILE exists and is a socket.

`-t FD'
     True if FD is a file descriptor that is associated with a terminal.



File: coreutils.info,  Node: Access permission tests,  Next: File characteristic tests,  Prev: File type tests,  Up: test invocation

16.3.2 Access permission tests
------------------------------

These options test for particular access permissions.

`-g FILE'
     True if FILE exists and has its set-group-ID bit set.

`-k FILE'
     True if FILE exists and has its "sticky" bit set.

`-r FILE'
     True if FILE exists and read permission is granted.

`-u FILE'
     True if FILE exists and has its set-user-ID bit set.

`-w FILE'
     True if FILE exists and write permission is granted.

`-x FILE'
     True if FILE exists and execute permission is granted (or search
     permission, if it is a directory).

`-O FILE'
     True if FILE exists and is owned by the current effective user ID.

`-G FILE'
     True if FILE exists and is owned by the current effective group ID.



File: coreutils.info,  Node: File characteristic tests,  Next: String tests,  Prev: Access permission tests,  Up: test invocation

16.3.3 File characteristic tests
--------------------------------

These options test other file characteristics.

`-e FILE'
     True if FILE exists.

`-s FILE'
     True if FILE exists and has a size greater than zero.

`FILE1 -nt FILE2'
     True if FILE1 is newer (according to modification date) than
     FILE2, or if FILE1 exists and FILE2 does not.

`FILE1 -ot FILE2'
     True if FILE1 is older (according to modification date) than
     FILE2, or if FILE2 exists and FILE1 does not.

`FILE1 -ef FILE2'
     True if FILE1 and FILE2 have the same device and inode numbers,
     i.e., if they are hard links to each other.



File: coreutils.info,  Node: String tests,  Next: Numeric tests,  Prev: File characteristic tests,  Up: test invocation

16.3.4 String tests
-------------------

These options test string characteristics.  You may need to quote
STRING arguments for the shell.  For example:

     test -n "$V"

   The quotes here prevent the wrong arguments from being passed to
`test' if `$V' is empty or contains special characters.

`-z STRING'
     True if the length of STRING is zero.

`-n STRING'
`STRING'
     True if the length of STRING is nonzero.

`STRING1 = STRING2'
     True if the strings are equal.

`STRING1 != STRING2'
     True if the strings are not equal.



File: coreutils.info,  Node: Numeric tests,  Next: Connectives for test,  Prev: String tests,  Up: test invocation

16.3.5 Numeric tests
--------------------

Numeric relationals.  The arguments must be entirely numeric (possibly
negative), or the special expression `-l STRING', which evaluates to
the length of STRING.

`ARG1 -eq ARG2'
`ARG1 -ne ARG2'
`ARG1 -lt ARG2'
`ARG1 -le ARG2'
`ARG1 -gt ARG2'
`ARG1 -ge ARG2'
     These arithmetic binary operators return true if ARG1 is equal,
     not-equal, less-than, less-than-or-equal, greater-than, or
     greater-than-or-equal than ARG2, respectively.


   For example:

     test -1 -gt -2 && echo yes
     => yes
     test -l abc -gt 1 && echo yes
     => yes
     test 0x100 -eq 1
     error--> test: integer expression expected before -eq


File: coreutils.info,  Node: Connectives for test,  Prev: Numeric tests,  Up: test invocation

16.3.6 Connectives for `test'
-----------------------------

The usual logical connectives.

`! EXPR'
     True if EXPR is false.

`EXPR1 -a EXPR2'
     True if both EXPR1 and EXPR2 are true.

`EXPR1 -o EXPR2'
     True if either EXPR1 or EXPR2 is true.



File: coreutils.info,  Node: expr invocation,  Prev: test invocation,  Up: Conditions

16.4 `expr': Evaluate expressions
=================================

`expr' evaluates an expression and writes the result on standard
output.  Each token of the expression must be a separate argument.

   Operands are either integers or strings.  Integers consist of one or
more decimal digits, with an optional leading `-'.  `expr' converts
anything appearing in an operand position to an integer or a string
depending on the operation being applied to it.

   Strings are not quoted for `expr' itself, though you may need to
quote them to protect characters with special meaning to the shell,
e.g., spaces.  However, regardless of whether it is quoted, a string
operand should not be a parenthesis or any of `expr''s operators like
`+', so you cannot safely pass an arbitrary string `$str' to expr
merely by quoting it to the shell.  One way to work around this is to
use the GNU extension `+', (e.g., `+ "$str" = foo'); a more portable
way is to use `" $str"' and to adjust the rest of the expression to take
the leading space into account (e.g., `" $str" = " foo"').

   You should not pass a negative integer or a string with leading `-'
as `expr''s first argument, as it might be misinterpreted as an option;
this can be avoided by parenthesization.  Also, portable scripts should
not use a string operand that happens to take the form of an integer;
this can be worked around by inserting leading spaces as mentioned
above.

   Operators may be given as infix symbols or prefix keywords.
Parentheses may be used for grouping in the usual manner.  You must
quote parentheses and many operators to avoid the shell evaluating them,
however.

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   Exit status:

     0 if the expression is neither null nor 0,
     1 if the expression is null or 0,
     2 if the expression is invalid,
     3 if an internal error occurred (e.g., arithmetic overflow).

* Menu:

* String expressions::          + : match substr index length
* Numeric expressions::         + - * / %
* Relations for expr::          | & < <= = == != >= >
* Examples of expr::            Examples.


File: coreutils.info,  Node: String expressions,  Next: Numeric expressions,  Up: expr invocation

16.4.1 String expressions
-------------------------

`expr' supports pattern matching and other string operators.  These
have lower precedence than both the numeric and relational operators (in
the next sections).

`STRING : REGEX'
     Perform pattern matching.  The arguments are converted to strings
     and the second is considered to be a (basic, a la GNU `grep')
     regular expression, with a `^' implicitly prepended.  The first
     argument is then matched against this regular expression.

     If the match succeeds and REGEX uses `\(' and `\)', the `:'
     expression returns the part of STRING that matched the
     subexpression; otherwise, it returns the number of characters
     matched.

     If the match fails, the `:' operator returns the null string if
     `\(' and `\)' are used in REGEX, otherwise 0.

     Only the first `\( ... \)' pair is relevant to the return value;
     additional pairs are meaningful only for grouping the regular
     expression operators.

     In the regular expression, `\+', `\?', and `\|' are operators
     which respectively match one or more, zero or one, or separate
     alternatives.  SunOS and other `expr''s treat these as regular
     characters.  (POSIX allows either behavior.)  *Note Regular
     Expression Library: (regex)Top, for details of regular expression
     syntax.  Some examples are in *Note Examples of expr::.

`match STRING REGEX'
     An alternative way to do pattern matching.  This is the same as
     `STRING : REGEX'.

`substr STRING POSITION LENGTH'
     Returns the substring of STRING beginning at POSITION with length
     at most LENGTH.  If either POSITION or LENGTH is negative, zero,
     or non-numeric, returns the null string.

`index STRING CHARSET'
     Returns the first position in STRING where the first character in
     CHARSET was found.  If no character in CHARSET is found in STRING,
     return 0.

`length STRING'
     Returns the length of STRING.

`+ TOKEN'
     Interpret TOKEN as a string, even if it is a keyword like MATCH or
     an operator like `/'.  This makes it possible to test `expr length
     + "$x"' or `expr + "$x" : '.*/\(.\)'' and have it do the right
     thing even if the value of $X happens to be (for example) `/' or
     `index'.  This operator is a GNU extension.  Portable shell
     scripts should use `" $token" : ' \(.*\)'' instead of `+ "$token"'.


   To make `expr' interpret keywords as strings, you must use the
`quote' operator.


File: coreutils.info,  Node: Numeric expressions,  Next: Relations for expr,  Prev: String expressions,  Up: expr invocation

16.4.2 Numeric expressions
--------------------------

`expr' supports the usual numeric operators, in order of increasing
precedence.  The string operators (previous section) have lower
precedence, the connectives (next section) have higher.

`+ -'
     Addition and subtraction.  Both arguments are converted to
     integers; an error occurs if this cannot be done.

`* / %'
     Multiplication, division, remainder.  Both arguments are converted
     to integers; an error occurs if this cannot be done.



File: coreutils.info,  Node: Relations for expr,  Next: Examples of expr,  Prev: Numeric expressions,  Up: expr invocation

16.4.3 Relations for `expr'
---------------------------

`expr' supports the usual logical connectives and relations.  These are
higher precedence than either the string or numeric operators (previous
sections).  Here is the list, lowest-precedence operator first.

`|'
     Returns its first argument if that is neither null nor zero,
     otherwise its second argument if it is neither null nor zero,
     otherwise 0.  It does not evaluate its second argument if its
     first argument is neither null nor zero.

`&'
     Return its first argument if neither argument is null or zero,
     otherwise 0.  It does not evaluate its second argument if its
     first argument is null or zero.

`< <= = == != >= >'
     Compare the arguments and return 1 if the relation is true, 0
     otherwise.  `==' is a synonym for `='.  `expr' first tries to
     convert both arguments to integers and do a numeric comparison; if
     either conversion fails, it does a lexicographic comparison using
     the character collating sequence specified by the `LC_COLLATE'
     locale.



File: coreutils.info,  Node: Examples of expr,  Prev: Relations for expr,  Up: expr invocation

16.4.4 Examples of using `expr'
-------------------------------

Here are a few examples, including quoting for shell metacharacters.

   To add 1 to the shell variable `foo', in Bourne-compatible shells:

     foo=`expr $foo + 1`

   To print the non-directory part of the file name stored in `$fname',
which need not contain a `/':

     expr $fname : '.*/\(.*\)' '|' $fname

   An example showing that `\+' is an operator:

     expr aaa : 'a\+'
     => 3

     expr abc : 'a\(.\)c'
     => b
     expr index abcdef cz
     => 3
     expr index index a
     error--> expr: syntax error
     expr index quote index a
     => 0


File: coreutils.info,  Node: Redirection,  Next: File name manipulation,  Prev: Conditions,  Up: Top

17 Redirection
**************

Unix shells commonly provide several forms of "redirection"--ways to
change the input source or output destination of a command.  But one
useful redirection is performed by a separate command, not by the shell;
it's described here.

* Menu:

* tee invocation::              Redirect output to multiple files.


File: coreutils.info,  Node: tee invocation,  Up: Redirection

17.1 `tee': Redirect output to multiple files
=============================================

The `tee' command copies standard input to standard output and also to
any files given as arguments.  This is useful when you want not only to
send some data down a pipe, but also to save a copy.  Synopsis:

     tee [OPTION]... [FILE]...

   If a file being written to does not already exist, it is created.
If a file being written to already exists, the data it previously
contained is overwritten unless the `-a' option is used.

   A FILE of `-' causes `tee' to send another copy of input to standard
output, but this is typically not that useful as the copies are
interleaved.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--append'
     Append standard input to the given files rather than overwriting
     them.

`-i'
`--ignore-interrupts'
     Ignore interrupt signals.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: File name manipulation,  Next: Working context,  Prev: Redirection,  Up: Top

18 File name manipulation
*************************

This section describes commands that manipulate file names.

* Menu:

* basename invocation::         Strip directory and suffix from a file name.
* dirname invocation::          Strip non-directory suffix from a file name.
* pathchk invocation::          Check file name portability.


File: coreutils.info,  Node: basename invocation,  Next: dirname invocation,  Up: File name manipulation

18.1 `basename': Strip directory and suffix from a file name
============================================================

`basename' removes any leading directory components from NAME.
Synopsis:

     basename NAME [SUFFIX]

   If SUFFIX is specified and is identical to the end of NAME, it is
removed from NAME as well.  Note that since trailing slashes are
removed prior to suffix matching, SUFFIX will do nothing if it contains
slashes.  `basename' prints the result on standard output.

   Together, `basename' and `dirname' are designed such that if `ls
"$name"' succeeds, then the command sequence `cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too.  This works for everything except
file names containing a trailing newline.

   POSIX allows the implementation to define the results if NAME is
empty or `//'.  In the former case, GNU `basename' returns the empty
string.  In the latter case, the result is `//' on platforms where //
is distinct from /, and `/' on platforms where there is no difference.

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output "sort".
     basename /usr/bin/sort

     # Output "stdio".
     basename include/stdio.h .h


File: coreutils.info,  Node: dirname invocation,  Next: pathchk invocation,  Prev: basename invocation,  Up: File name manipulation

18.2 `dirname': Strip non-directory suffix from a file name
===========================================================

`dirname' prints all but the final slash-delimited component of a
string (presumably a file name).  Synopsis:

     dirname NAME

   If NAME is a single component, `dirname' prints `.' (meaning the
current directory).

   Together, `basename' and `dirname' are designed such that if `ls
"$name"' succeeds, then the command sequence `cd "$(dirname "$name")";
ls "$(basename "$name")"' will, too.  This works for everything except
file names containing a trailing newline.

   POSIX allows the implementation to define the results if NAME is
`//'.  With GNU `dirname', the result is `//' on platforms where // is
distinct from /, and `/' on platforms where there is no difference.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

   Examples:

     # Output "/usr/bin".
     dirname /usr/bin/sort

     # Output ".".
     dirname stdio.h


File: coreutils.info,  Node: pathchk invocation,  Prev: dirname invocation,  Up: File name manipulation

18.3 `pathchk': Check file name portability
===========================================

`pathchk' checks portability of file names.  Synopsis:

     pathchk [OPTION]... NAME...

   For each NAME, `pathchk' prints a message if any of these conditions
is true:

  1. One of the existing directories in NAME does not have search
     (execute) permission,

  2. The length of NAME is larger than the maximum supported by the
     operating system.

  3. The length of one component of NAME is longer than its file
     system's maximum.

   A nonexistent NAME is not an error, so long a file with that name
could be created under the above conditions.

   The program accepts the following options.  Also see *Note Common
options::.  Options must precede operands.

`-p'
     Instead of performing checks based on the underlying file system,
     print a message if any of these conditions is true:

       1. A file name is empty.

       2. The length of a file name or one of its components exceeds the
          POSIX minimum limits for portability.

       3. A file name contains a character outside the portable file
          name character set, namely, the ASCII letters and digits, `-',
          `.', `/', and `_'.

`-P'
     Print a message if a file name is empty, or if it contains a
     component that begins with `-'.

`--portability'
     Print a message if a file name is not portable to all POSIX hosts.
     This option is equivalent to `-p -P'.


   Exit status:

     0 if all specified file names passed all checks,
     1 otherwise.


File: coreutils.info,  Node: Working context,  Next: User information,  Prev: File name manipulation,  Up: Top

19 Working context
******************

This section describes commands that display or alter the context in
which you are working: the current directory, the terminal settings, and
so forth.  See also the user-related commands in the next section.

* Menu:

* pwd invocation::              Print working directory.
* stty invocation::             Print or change terminal characteristics.
* printenv invocation::         Print environment variables.
* tty invocation::              Print file name of terminal on standard input.


File: coreutils.info,  Node: pwd invocation,  Next: stty invocation,  Up: Working context

19.1 `pwd': Print working directory
===================================

`pwd' prints the fully resolved name of the current directory.  That
is, all components of the printed name will be actual directory
names--none will be symbolic links.

   Because most shells have a built-in `pwd' command, using an
unadorned `pwd' in a script or interactively may get you different
functionality than that described here.

   The only options are a lone `--help' or `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: stty invocation,  Next: printenv invocation,  Prev: pwd invocation,  Up: Working context

19.2 `stty': Print or change terminal characteristics
=====================================================

`stty' prints or changes terminal characteristics, such as baud rate.
Synopses:

     stty [OPTION] [SETTING]...
     stty [OPTION]

   If given no line settings, `stty' prints the baud rate, line
discipline number (on systems that support it), and line settings that
have been changed from the values set by `stty sane'.  By default, mode
reading and setting are performed on the tty line connected to standard
input, although this can be modified by the `--file' option.

   `stty' accepts many non-option arguments that change aspects of the
terminal line operation, as described below.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--all'
     Print all current settings in human-readable form.  This option
     may not be used in combination with any line settings.

`-F DEVICE'
`--file=DEVICE'
     Set the line opened by the file name specified in DEVICE instead of
     the tty line connected to standard input.  This option is necessary
     because opening a POSIX tty requires use of the `O_NONDELAY' flag
     to prevent a POSIX tty from blocking until the carrier detect line
     is high if the `clocal' flag is not set.  Hence, it is not always
     possible to allow the shell to open the device in the traditional
     manner.

`-g'
`--save'
     Print all current settings in a form that can be used as an
     argument to another `stty' command to restore the current
     settings.  This option may not be used in combination with any
     line settings.


   Many settings can be turned off by preceding them with a `-'.  Such
arguments are marked below with "May be negated" in their description.
The descriptions themselves refer to the positive case, that is, when
_not_ negated (unless stated otherwise, of course).

   Some settings are not available on all POSIX systems, since they use
extensions.  Such arguments are marked below with "Non-POSIX" in their
description.  On non-POSIX systems, those or other settings also may not
be available, but it's not feasible to document all the variations: just
try it and see.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Control::                     Control settings
* Input::                       Input settings
* Output::                      Output settings
* Local::                       Local settings
* Combination::                 Combination settings
* Characters::                  Special characters
* Special::                     Special settings


File: coreutils.info,  Node: Control,  Next: Input,  Up: stty invocation

19.2.1 Control settings
-----------------------

Control settings:

`parenb'
     Generate parity bit in output and expect parity bit in input.  May
     be negated.

`parodd'
     Set odd parity (even if negated).  May be negated.

`cs5'
`cs6'
`cs7'
`cs8'
     Set character size to 5, 6, 7, or 8 bits.

`hup'
`hupcl'
     Send a hangup signal when the last process closes the tty.  May be
     negated.

`cstopb'
     Use two stop bits per character (one if negated).  May be negated.

`cread'
     Allow input to be received.  May be negated.

`clocal'
     Disable modem control signals.  May be negated.

`crtscts'
     Enable RTS/CTS flow control.  Non-POSIX.  May be negated.


File: coreutils.info,  Node: Input,  Next: Output,  Prev: Control,  Up: stty invocation

19.2.2 Input settings
---------------------

`ignbrk'
     Ignore break characters.  May be negated.

`brkint'
     Make breaks cause an interrupt signal.  May be negated.

`ignpar'
     Ignore characters with parity errors.  May be negated.

`parmrk'
     Mark parity errors (with a 255-0-character sequence).  May be
     negated.

`inpck'
     Enable input parity checking.  May be negated.

`istrip'
     Clear high (8th) bit of input characters.  May be negated.

`inlcr'
     Translate newline to carriage return.  May be negated.

`igncr'
     Ignore carriage return.  May be negated.

`icrnl'
     Translate carriage return to newline.  May be negated.

`iutf8'
     Assume input characters are UTF-8 encoded.  May be negated.

`ixon'
     Enable XON/XOFF flow control (that is, `CTRL-S'/`CTRL-Q').  May be
     negated.

`ixoff'
`tandem'
     Enable sending of `stop' character when the system input buffer is
     almost full, and `start' character when it becomes almost empty
     again.  May be negated.

`iuclc'
     Translate uppercase characters to lowercase.  Non-POSIX.  May be
     negated.

`ixany'
     Allow any character to restart output (only the start character if
     negated).  Non-POSIX.  May be negated.

`imaxbel'
     Enable beeping and not flushing input buffer if a character arrives
     when the input buffer is full.  Non-POSIX.  May be negated.


File: coreutils.info,  Node: Output,  Next: Local,  Prev: Input,  Up: stty invocation

19.2.3 Output settings
----------------------

These arguments specify output-related operations.

`opost'
     Postprocess output.  May be negated.

`olcuc'
     Translate lowercase characters to uppercase.  Non-POSIX.  May be
     negated.

`ocrnl'
     Translate carriage return to newline.  Non-POSIX.  May be negated.

`onlcr'
     Translate newline to carriage return-newline.  Non-POSIX.  May be
     negated.

`onocr'
     Do not print carriage returns in the first column.  Non-POSIX.
     May be negated.

`onlret'
     Newline performs a carriage return.  Non-POSIX.  May be negated.

`ofill'
     Use fill (padding) characters instead of timing for delays.
     Non-POSIX.  May be negated.

`ofdel'
     Use delete characters for fill instead of null characters.
     Non-POSIX.  May be negated.

`nl1'
`nl0'
     Newline delay style.  Non-POSIX.

`cr3'
`cr2'
`cr1'
`cr0'
     Carriage return delay style.  Non-POSIX.

`tab3'
`tab2'
`tab1'
`tab0'
     Horizontal tab delay style.  Non-POSIX.

`bs1'
`bs0'
     Backspace delay style.  Non-POSIX.

`vt1'
`vt0'
     Vertical tab delay style.  Non-POSIX.

`ff1'
`ff0'
     Form feed delay style.  Non-POSIX.


File: coreutils.info,  Node: Local,  Next: Combination,  Prev: Output,  Up: stty invocation

19.2.4 Local settings
---------------------

`isig'
     Enable `interrupt', `quit', and `suspend' special characters.  May
     be negated.

`icanon'
     Enable `erase', `kill', `werase', and `rprnt' special characters.
     May be negated.

`iexten'
     Enable non-POSIX special characters.  May be negated.

`echo'
     Echo input characters.  May be negated.

`echoe'
`crterase'
     Echo `erase' characters as backspace-space-backspace.  May be
     negated.

`echok'
     Echo a newline after a `kill' character.  May be negated.

`echonl'
     Echo newline even if not echoing other characters.  May be negated.

`noflsh'
     Disable flushing after `interrupt' and `quit' special characters.
     May be negated.

`xcase'
     Enable input and output of uppercase characters by preceding their
     lowercase equivalents with `\', when `icanon' is set.  Non-POSIX.
     May be negated.

`tostop'
     Stop background jobs that try to write to the terminal.  Non-POSIX.
     May be negated.

`echoprt'
`prterase'
     Echo erased characters backward, between `\' and `/'.  Non-POSIX.
     May be negated.

`echoctl'
`ctlecho'
     Echo control characters in hat notation (`^C') instead of
     literally.  Non-POSIX.  May be negated.

`echoke'
`crtkill'
     Echo the `kill' special character by erasing each character on the
     line as indicated by the `echoprt' and `echoe' settings, instead
     of by the `echoctl' and `echok' settings.  Non-POSIX.  May be
     negated.


File: coreutils.info,  Node: Combination,  Next: Characters,  Prev: Local,  Up: stty invocation

19.2.5 Combination settings
---------------------------

Combination settings:

`evenp'
`parity'
     Same as `parenb -parodd cs7'.  May be negated.  If negated, same
     as `-parenb cs8'.

`oddp'
     Same as `parenb parodd cs7'.  May be negated.  If negated, same as
     `-parenb cs8'.

`nl'
     Same as `-icrnl -onlcr'.  May be negated.  If negated, same as
     `icrnl -inlcr -igncr onlcr -ocrnl -onlret'.

`ek'
     Reset the `erase' and `kill' special characters to their default
     values.

`sane'
     Same as:

          cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
          -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
          -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
          ff0 isig icanon iexten echo echoe echok -echonl
          -noflsh -xcase -tostop -echoprt echoctl echoke

     and also sets all special characters to their default values.

`cooked'
     Same as `brkint ignpar istrip icrnl ixon opost isig icanon', plus
     sets the `eof' and `eol' characters to their default values if
     they are the same as the `min' and `time' characters.  May be
     negated.  If negated, same as `raw'.

`raw'
     Same as:

          -ignbrk -brkint -ignpar -parmrk -inpck -istrip
          -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
          -imaxbel -opost -isig -icanon -xcase min 1 time 0

     May be negated.  If negated, same as `cooked'.

`cbreak'
     Same as `-icanon'.  May be negated.  If negated, same as `icanon'.

`pass8'
     Same as `-parenb -istrip cs8'.  May be negated.  If negated, same
     as `parenb istrip cs7'.

`litout'
     Same as `-parenb -istrip -opost cs8'.  May be negated.  If
     negated, same as `parenb istrip opost cs7'.

`decctlq'
     Same as `-ixany'.  Non-POSIX.  May be negated.

`tabs'
     Same as `tab0'.  Non-POSIX.  May be negated.  If negated, same as
     `tab3'.

`lcase'
`LCASE'
     Same as `xcase iuclc olcuc'.  Non-POSIX.  May be negated.

`crt'
     Same as `echoe echoctl echoke'.

`dec'
     Same as `echoe echoctl echoke -ixany intr ^C erase ^? kill C-u'.


File: coreutils.info,  Node: Characters,  Next: Special,  Prev: Combination,  Up: stty invocation

19.2.6 Special characters
-------------------------

The special characters' default values vary from system to system.
They are set with the syntax `name value', where the names are listed
below and the value can be given either literally, in hat notation
(`^C'), or as an integer which may start with `0x' to indicate
hexadecimal, `0' to indicate octal, or any other digit to indicate
decimal.

   For GNU stty, giving a value of `^-' or `undef' disables that
special character.  (This is incompatible with Ultrix `stty', which
uses  a value of `u' to disable a special character.  GNU `stty' treats
a value `u' like any other, namely to set that special character to
<U>.)

`intr'
     Send an interrupt signal.

`quit'
     Send a quit signal.

`erase'
     Erase the last character typed.

`kill'
     Erase the current line.

`eof'
     Send an end of file (terminate the input).

`eol'
     End the line.

`eol2'
     Alternate character to end the line.  Non-POSIX.

`swtch'
     Switch to a different shell layer.  Non-POSIX.

`start'
     Restart the output after stopping it.

`stop'
     Stop the output.

`susp'
     Send a terminal stop signal.

`dsusp'
     Send a terminal stop signal after flushing the input.  Non-POSIX.

`rprnt'
     Redraw the current line.  Non-POSIX.

`werase'
     Erase the last word typed.  Non-POSIX.

`lnext'
     Enter the next character typed literally, even if it is a special
     character.  Non-POSIX.


File: coreutils.info,  Node: Special,  Prev: Characters,  Up: stty invocation

19.2.7 Special settings
-----------------------

`min N'
     Set the minimum number of characters that will satisfy a read until
     the time value has expired, when `-icanon' is set.

`time N'
     Set the number of tenths of a second before reads time out if the
     minimum number of characters have not been read, when `-icanon' is
     set.

`ispeed N'
     Set the input speed to N.

`ospeed N'
     Set the output speed to N.

`rows N'
     Tell the tty kernel driver that the terminal has N rows.
     Non-POSIX.

`cols N'
`columns N'
     Tell the kernel that the terminal has N columns.  Non-POSIX.

`size'
     Print the number of rows and columns that the kernel thinks the
     terminal has.  (Systems that don't support rows and columns in the
     kernel typically use the environment variables `LINES' and
     `COLUMNS' instead; however, GNU `stty' does not know anything
     about them.)  Non-POSIX.

`line N'
     Use line discipline N.  Non-POSIX.

`speed'
     Print the terminal speed.

`N'
     Set the input and output speeds to N.  N can be one of: 0 50 75
     110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200 38400
     `exta' `extb'.  `exta' is the same as 19200; `extb' is the same as
     38400.  0 hangs up the line if `-clocal' is set.


File: coreutils.info,  Node: printenv invocation,  Next: tty invocation,  Prev: stty invocation,  Up: Working context

19.3 `printenv': Print all or some environment variables
========================================================

`printenv' prints environment variable values.  Synopsis:

     printenv [OPTION] [VARIABLE]...

   If no VARIABLEs are specified, `printenv' prints the value of every
environment variable.  Otherwise, it prints the value of each VARIABLE
that is set, and nothing for those that are not set.

   The only options are a lone `--help' or `--version'.  *Note Common
options::.

   Exit status:

     0 if all variables specified were found
     1 if at least one specified variable was not found
     2 if a write error occurred


File: coreutils.info,  Node: tty invocation,  Prev: printenv invocation,  Up: Working context

19.4 `tty': Print file name of terminal on standard input
=========================================================

`tty' prints the file name of the terminal connected to its standard
input.  It prints `not a tty' if standard input is not a terminal.
Synopsis:

     tty [OPTION]...

   The program accepts the following option.  Also see *Note Common
options::.

`-s'
`--silent'
`--quiet'
     Print nothing; only return an exit status.


   Exit status:

     0 if standard input is a terminal
     1 if standard input is not a terminal
     2 if given incorrect arguments
     3 if a write error occurs


File: coreutils.info,  Node: User information,  Next: System context,  Prev: Working context,  Up: Top

20 User information
*******************

This section describes commands that print user-related information:
logins, groups, and so forth.

* Menu:

* id invocation::               Print user identity.
* logname invocation::          Print current login name.
* whoami invocation::           Print effective user ID.
* groups invocation::           Print group names a user is in.
* users invocation::            Print login names of users currently logged in.
* who invocation::              Print who is currently logged in.


File: coreutils.info,  Node: id invocation,  Next: logname invocation,  Up: User information

20.1 `id': Print user identity
==============================

`id' prints information about the given user, or the process running it
if no user is specified.  Synopsis:

     id [OPTION]... [USERNAME]

   By default, it prints the real user ID, real group ID, effective
user ID if different from the real user ID, effective group ID if
different from the real group ID, and supplemental group IDs.

   Each of these numeric values is preceded by an identifying string and
followed by the corresponding user or group name in parentheses.

   The options cause `id' to print only part of the above information.
Also see *Note Common options::.

`-g'
`--group'
     Print only the group ID.

`-G'
`--groups'
     Print only the group ID and the supplementary groups.

`-n'
`--name'
     Print the user or group name instead of the ID number.  Requires
     `-u', `-g', or `-G'.

`-r'
`--real'
     Print the real, instead of effective, user or group ID.  Requires
     `-u', `-g', or `-G'.

`-u'
`--user'
     Print only the user ID.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: logname invocation,  Next: whoami invocation,  Prev: id invocation,  Up: User information

20.2 `logname': Print current login name
========================================

`logname' prints the calling user's name, as found in a
system-maintained file (often `/var/run/utmp' or `/etc/utmp'), and
exits with a status of 0.  If there is no entry for the calling
process, `logname' prints an error message and exits with a status of 1.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: whoami invocation,  Next: groups invocation,  Prev: logname invocation,  Up: User information

20.3 `whoami': Print effective user ID
======================================

`whoami' prints the user name associated with the current effective
user ID.  It is equivalent to the command `id -un'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: groups invocation,  Next: users invocation,  Prev: whoami invocation,  Up: User information

20.4 `groups': Print group names a user is in
=============================================

`groups' prints the names of the primary and any supplementary groups
for each given USERNAME, or the current process if no names are given.
If more than one name is given, the name of each user is printed before
the list of that user's groups.  Synopsis:

     groups [USERNAME]...

   The group lists are equivalent to the output of the command `id -Gn'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: users invocation,  Next: who invocation,  Prev: groups invocation,  Up: User information

20.5 `users': Print login names of users currently logged in
============================================================

`users' prints on a single line a blank-separated list of user names of
users currently logged in to the current host.  Each user name
corresponds to a login session, so if a user has more than one login
session, that user's name will appear the same number of times in the
output.  Synopsis:

     users [FILE]

   With no FILE argument, `users' extracts its information from a
system-maintained file (often `/var/run/utmp' or `/etc/utmp').  If a
file argument is given, `users' uses that file instead.  A common
choice is `/var/log/wtmp'.

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: who invocation,  Prev: users invocation,  Up: User information

20.6 `who': Print who is currently logged in
============================================

`who' prints information about users who are currently logged on.
Synopsis:

     `who' [OPTION] [FILE] [am i]

   If given no non-option arguments, `who' prints the following
information for each user currently logged on: login name, terminal
line, login time, and remote hostname or X display.

   If given one non-option argument, `who' uses that instead of a
default system-maintained file (often `/var/run/utmp' or `/etc/utmp')
as the name of the file containing the record of users logged on.
`/var/log/wtmp' is commonly given as an argument to `who' to look at
who has previously logged on.

   If given two non-option arguments, `who' prints only the entry for
the user running it (determined from its standard input), preceded by
the hostname.  Traditionally, the two arguments given are `am i', as in
`who am i'.

   Time stamps are listed according to the time zone rules specified by
the `TZ' environment variable, or by the system default rules if `TZ'
is not set.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--all'
     Same as `-b -d --login -p -r -t -T -u'.

`-b'
`--boot'
     Print the date and time of last system boot.

`-d'
`--dead'
     Print information corresponding to dead processes.

`-H'
`--heading'
     Print column headings.

`-m'
     Same as `who am i'.

`-q'
`--count'
     Print only the login names and the number of users logged on.
     Overrides all other options.

`-s'
     Ignored; for compatibility with other versions of `who'.

`-u'
     After the login time, print the number of hours and minutes that
     the user has been idle.  `.' means the user was active in the last
     minute.  `old' means the user has been idle for more than 24 hours.

`-l'
`--login'
     List only the entries that correspond to processes via which the
     system is waiting for a user to login.  The user name is always
     `LOGIN'.

`--lookup'
     Attempt to canonicalize hostnames found in utmp through a DNS
     lookup.  This is not the default because it can cause significant
     delays on systems with automatic dial-up internet access.

`-H'
`--heading'
     Print a line of column headings.

`-w'
`-T'
`--mesg'
`--message'
`--writable'
     After each login name print a character indicating the user's
     message status:

          `+' allowing `write' messages
          `-' disallowing `write' messages
          `?' cannot find terminal device


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: System context,  Next: Modified command invocation,  Prev: User information,  Up: Top

21 System context
*****************

This section describes commands that print or change system-wide
information.

* Menu:

* date invocation::             Print or set system date and time.
* uname invocation::            Print system information.
* hostname invocation::         Print or set system name.
* hostid invocation::           Print numeric host identifier.


File: coreutils.info,  Node: date invocation,  Next: uname invocation,  Up: System context

21.1 `date': Print or set system date and time
==============================================

Synopses:

     date [OPTION]... [+FORMAT]
     date [-u|--utc|--universal] [ MMDDhhmm[[CC]YY][.ss] ]

   Invoking `date' with no FORMAT argument is equivalent to invoking it
with a default format that depends on the `LC_TIME' locale category.
In the default C locale, this format is `'+%a %b %e %H:%M:%S %Z %Y'',
so the output looks like `Thu Mar  3 13:47:51 PST 2005'.

   Normally, `date' uses the time zone rules indicated by the `TZ'
environment variable, or the system default rules if `TZ' is not set.
*Note Specifying the Time Zone with `TZ': (libc)TZ Variable.

   If given an argument that starts with a `+', `date' prints the
current date and time (or the date and time specified by the `--date'
option, see below) in the format defined by that argument, which is
similar to that of the `strftime' function.  Except for conversion
specifiers, which start with `%', characters in the format string are
printed unchanged.  The conversion specifiers are described below.

   An exit status of zero indicates success, and a nonzero value
indicates failure.

* Menu:

* Time conversion specifiers::     %[HIklMNpPrRsSTXzZ]
* Date conversion specifiers::     %[aAbBcCdDeFgGhjmuUVwWxyY]
* Literal conversion specifiers::  %[%nt]
* Padding and other flags::        Pad with zeros, spaces, etc.
* Setting the time::               Changing the system clock.
* Options for date::               Instead of the current time.
* Examples of date::               Examples.


File: coreutils.info,  Node: Time conversion specifiers,  Next: Date conversion specifiers,  Up: date invocation

21.1.1 Time conversion specifiers
---------------------------------

`date' conversion specifiers related to times.

`%H'
     hour (`00'...`23')

`%I'
     hour (`01'...`12')

`%k'
     hour (` 0'...`23').  This is a GNU extension.

`%l'
     hour (` 1'...`12').  This is a GNU extension.

`%M'
     minute (`00'...`59')

`%N'
     nanoseconds (`000000000'...`999999999').  This is a GNU extension.

`%p'
     locale's equivalent of either `AM' or `PM'; blank in many locales.
     Noon is treated as `PM' and midnight as `AM'.

`%P'
     like `%p', except lower case.  This is a GNU extension.

`%r'
     locale's 12-hour clock time (e.g., `11:11:04 PM')

`%R'
     24-hour hour and minute.  Same as `%H:%M'.  This is a GNU
     extension.

`%s'
     seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
     Leap seconds are not counted unless leap second support is
     available.  *Note %s-examples::, for examples.  This is a GNU
     extension.

`%S'
     second (`00'...`60').  This may be `60' if leap seconds are
     supported.

`%T'
     24-hour hour, minute, and second.  Same as `%H:%M:%S'.

`%X'
     locale's time representation (e.g., `23:13:48')

`%z'
     RFC 2822/ISO 8601 style numeric time zone (e.g., `-0600' or
     `+0530'), or nothing if no time zone is determinable.  This value
     reflects the numeric time zone appropriate for the current time,
     using the time zone rules specified by the `TZ' environment
     variable.  The time (and optionally, the time zone rules) can be
     overridden by the `--date' option.  This is a GNU extension.

`%:z'
     RFC 3339/ISO 8601 style numeric time zone with `:' (e.g., `-06:00'
     or `+05:30'), or nothing if no time zone is determinable.  This is
     a GNU extension.

`%::z'
     Numeric time zone to the nearest second with `:' (e.g.,
     `-06:00:00' or `+05:30:00'), or nothing if no time zone is
     determinable.  This is a GNU extension.

`%:::z'
     Numeric time zone with `:' using the minimum necessary precision
     (e.g., `-06', `+05:30', or `-04:56:02'), or nothing if no time
     zone is determinable.  This is a GNU extension.

`%Z'
     alphabetic time zone abbreviation (e.g., `EDT'), or nothing if no
     time zone is determinable.  See `%z' for how it is determined.


File: coreutils.info,  Node: Date conversion specifiers,  Next: Literal conversion specifiers,  Prev: Time conversion specifiers,  Up: date invocation

21.1.2 Date conversion specifiers
---------------------------------

`date' conversion specifiers related to dates.

`%a'
     locale's abbreviated weekday name (e.g., `Sun')

`%A'
     locale's full weekday name, variable length (e.g., `Sunday')

`%b'
     locale's abbreviated month name (e.g., `Jan')

`%B'
     locale's full month name, variable length (e.g., `January')

`%c'
     locale's date and time (e.g., `Thu Mar  3 23:05:25 2005')

`%C'
     century.  This is like `%Y', except the last two digits are
     omitted.  For example, it is `20' if `%Y' is `2000', and is `-0'
     if `%Y' is `-001'.  It is normally at least two characters, but it
     may be more.

`%d'
     day of month (e.g., `01')

`%D'
     date; same as `%m/%d/%y'

`%e'
     day of month, space padded; same as `%_d'

`%F'
     full date in ISO 8601 format; same as `%Y-%m-%d'.  This is a good
     choice for a date format, as it is standard and is easy to sort in
     the usual case where years are in the range 0000...9999.  This is
     a GNU extension.

`%g'
     year corresponding to the ISO week number, but without the century
     (range `00' through `99').  This has the same format and value as
     `%y', except that if the ISO week number (see `%V') belongs to the
     previous or next year, that year is used instead.  This is a GNU
     extension.

`%G'
     year corresponding to the ISO week number.  This has the same
     format and value as `%Y', except that if the ISO week number (see
     `%V') belongs to the previous or next year, that year is used
     instead.  It is normally useful only if `%V' is also used; for
     example, the format `%G-%m-%d' is probably a mistake, since it
     combines the ISO week number year with the conventional month and
     day.  This is a GNU extension.

`%h'
     same as `%b'

`%j'
     day of year (`001'...`366')

`%m'
     month (`01'...`12')

`%u'
     day of week (`1'...`7') with `1' corresponding to Monday

`%U'
     week number of year, with Sunday as the first day of the week
     (`00'...`53').  Days in a new year preceding the first Sunday are
     in week zero.

`%V'
     ISO week number, that is, the week number of year, with Monday as
     the first day of the week (`01'...`53').  If the week containing
     January 1 has four or more days in the new year, then it is
     considered week 1; otherwise, it is week 53 of the previous year,
     and the next week is week 1.  (See the ISO 8601 standard.)

`%w'
     day of week (`0'...`6') with 0 corresponding to Sunday

`%W'
     week number of year, with Monday as first day of week
     (`00'...`53').  Days in a new year preceding the first Monday are
     in week zero.

`%x'
     locale's date representation (e.g., `12/31/99')

`%y'
     last two digits of year (`00'...`99')

`%Y'
     year.  This is normally at least four characters, but it may be
     more.  Year `0000' precedes year `0001', and year `-001' precedes
     year `0000'.


File: coreutils.info,  Node: Literal conversion specifiers,  Next: Padding and other flags,  Prev: Date conversion specifiers,  Up: date invocation

21.1.3 Literal conversion specifiers
------------------------------------

`date' conversion specifiers that produce literal strings.

`%%'
     a literal %

`%n'
     a newline

`%t'
     a horizontal tab


File: coreutils.info,  Node: Padding and other flags,  Next: Setting the time,  Prev: Literal conversion specifiers,  Up: date invocation

21.1.4 Padding and other flags
------------------------------

Unless otherwise specified, `date' normally pads numeric fields with
zeros, so that, for example, numeric months are always output as two
digits.  Seconds since the epoch are not padded, though, since there is
no natural width for them.

   As a GNU extension, `date' recognizes any of the following optional
flags after the `%':

`-'
     (hyphen) Do not pad the field; useful if the output is intended for
     human consumption.

`_'
     (underscore) Pad with spaces; useful if you need a fixed number of
     characters in the output, but zeros are too distracting.

`0'
     (zero) Pad with zeros even if the conversion specifier would
     normally pad with spaces.

`^'
     Use upper case characters if possible.

`#'
     Use opposite case characters if possible.  A field that is
     normally upper case becomes lower case, and vice versa.

Here are some examples of padding:

     date +%d/%m -d "Feb 1"
     => 01/02
     date +%-d/%-m -d "Feb 1"
     => 1/2
     date +%_d/%_m -d "Feb 1"
     =>  1/ 2

   As a GNU extension, you can specify the field width (after any flag,
if present) as a decimal number.  If the natural size of the output is
of the field has less than the specified number of characters, the
result is written right adjusted and padded to the given size.  For
example, `%9B' prints the right adjusted month name in a field of width
9.

   An optional modifier can follow the optional flag and width
specification.  The modifiers are:

`E'
     Use the locale's alternate representation for date and time.  This
     modifier applies to the `%c', `%C', `%x', `%X', `%y' and `%Y'
     conversion specifiers.  In a Japanese locale, for example, `%Ex'
     might yield a date format based on the Japanese Emperors' reigns.

`O'
     Use the locale's alternate numeric symbols for numbers.  This
     modifier applies only to numeric conversion specifiers.

   If the format supports the modifier but no alternate representation
is available, it is ignored.


File: coreutils.info,  Node: Setting the time,  Next: Options for date,  Prev: Padding and other flags,  Up: date invocation

21.1.5 Setting the time
-----------------------

If given an argument that does not start with `+', `date' sets the
system clock to the date and time specified by that argument (as
described below).  You must have appropriate privileges to set the
system clock.  The `--date' and `--set' options may not be used with
such an argument.  The `--universal' option may be used with such an
argument to indicate that the specified date and time are relative to
Coordinated Universal Time rather than to the local time zone.

   The argument must consist entirely of digits, which have the
following meaning:

`MM'
     month

`DD'
     day within month

`hh'
     hour

`mm'
     minute

`CC'
     first two digits of year (optional)

`YY'
     last two digits of year (optional)

`ss'
     second (optional)

   The `--set' option also sets the system clock; see the next section.


File: coreutils.info,  Node: Options for date,  Next: Examples of date,  Prev: Setting the time,  Up: date invocation

21.1.6 Options for `date'
-------------------------

The program accepts the following options.  Also see *Note Common
options::.

`-d DATESTR'
`--date=DATESTR'
     Display the date and time specified in DATESTR instead of the
     current date and time.  DATESTR can be in almost any common
     format.  It can contain month names, time zones, `am' and `pm',
     `yesterday', etc.  For example, `--date="2004-02-27
     14:19:13.489392193 +0530"' specifies the instant of time that is
     489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
     time zone that is 5 hours and 30 minutes east of UTC.  *Note Date
     input formats::.

`-f DATEFILE'
`--file=DATEFILE'
     Parse each line in DATEFILE as with `-d' and display the resulting
     date and time.  If DATEFILE is `-', use standard input.  This is
     useful when you have many dates to process, because the system
     overhead of starting up the `date' executable many times can be
     considerable.

`-r FILE'
`--reference=FILE'
     Display the date and time of the last modification of FILE,
     instead of the current date and time.

`-R'
`--rfc-822'
`--rfc-2822'
     Display the date and time using the format `%a, %d %b %Y %H:%M:%S
     %z', evaluated in the C locale so abbreviations are always in
     English.  For example:

          Fri, 09 Sep 2005 13:51:39 -0700

     This format conforms to Internet RFCs 2822
     (ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt) and 822
     (ftp://ftp.rfc-editor.org/in-notes/rfc822.txt), the current and
     previous standards for Internet email.

`--rfc-3339=TIMESPEC'
     Display the date using a format specified by Internet RFC 3339
     (ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt).  This is a subset
     of the ISO 8601 format, except that it also permits applications
     to use a space rather than a `T' to separate dates from times.
     Unlike the other standard formats, RFC 3339 format is always
     suitable as input for the `--date' (`-d') and `--file' (`-f')
     options, regardless of the current locale.

     The argument TIMESPEC specifies how much of the time to include.
     It can be one of the following:

    `date'
          Print just the full-date, e.g., `2005-09-14'.  This is
          equivalent to the format `%Y-%m-%d'.

    `seconds'
          Print the full-date and full-time separated by a space, e.g.,
          `2005-09-14 00:56:06+05:30'.  The output ends with a numeric
          time-offset; here the `+05:30' means that local time is five
          hours and thirty minutes east of UTC.  This is equivalent to
          the format `%Y-%m-%d %H:%M:%S%:z'.

    `ns'
          Like `seconds', but also print nanoseconds, e.g., `2005-09-14
          00:56:06.998458565+05:30'.  This is equivalent to the format
          `%Y-%m-%d %H:%M:%S.%N%:z'.


`-s DATESTR'
`--set=DATESTR'
     Set the date and time to DATESTR.  See `-d' above.

`-u'
`--utc'
`--universal'
     Use Coordinated Universal Time (UTC) by operating as if the `TZ'
     environment variable were set to the string `UTC0'.  Coordinated
     Universal Time is often called "Greenwich Mean Time" (GMT) for
     historical reasons.


File: coreutils.info,  Node: Examples of date,  Prev: Options for date,  Up: date invocation

21.1.7 Examples of `date'
-------------------------

Here are a few examples.  Also see the documentation for the `-d'
option in the previous section.

   * To print the date of the day before yesterday:

          date --date='2 days ago'

   * To print the date of the day three months and one day hence:

          date --date='3 months 1 day'

   * To print the day of year of Christmas in the current year:

          date --date='25 Dec' +%j

   * To print the current full month name and the day of the month:

          date '+%B %d'

     But this may not be what you want because for the first nine days
     of the month, the `%d' expands to a zero-padded two-digit field,
     for example `date -d 1may '+%B %d'' will print `May 01'.

   * To print a date without the leading zero for one-digit days of the
     month, you can use the (GNU extension) `-' flag to suppress the
     padding altogether:

          date -d 1may '+%B %-d

   * To print the current date and time in the format required by many
     non-GNU versions of `date' when setting the system clock:

          date +%m%d%H%M%Y.%S

   * To set the system clock forward by two minutes:

          date --set='+2 minutes'

   * To print the date in RFC 2822 format, use `date --rfc-2822'.  Here
     is some example output:

          Fri, 09 Sep 2005 13:51:39 -0700

   * To convert a date string to the number of seconds since the epoch
     (which is 1970-01-01 00:00:00 UTC), use the `--date' option with
     the `%s' format.  That can be useful in sorting and/or graphing
     and/or comparing data by date.  The following command outputs the
     number of the seconds since the epoch for the time two minutes
     after the epoch:

          date --date='1970-01-01 00:02:00 +0000' +%s
          120

     If you do not specify time zone information in the date string,
     `date' uses your computer's idea of the time zone when
     interpreting the string.  For example, if your computer's time
     zone is that of Cambridge, Massachusetts, which was then 5 hours
     (i.e., 18,000 seconds) behind UTC:

          # local time zone used
          date --date='1970-01-01 00:02:00' +%s
          18120

   * If you're sorting or graphing dated data, your raw date values may
     be represented as seconds since the epoch.  But few people can
     look at the date `946684800' and casually note "Oh, that's the
     first second of the year 2000 in Greenwich, England."

          date --date='2000-01-01 UTC' +%s
          946684800

     An alternative is to use the `--utc' (`-u') option.  Then you may
     omit `UTC' from the date string.  Although this produces the same
     result for `%s' and many other format sequences, with a time zone
     offset different from zero, it would give a different result for
     zone-dependent formats like `%z'.

          date -u --date=2000-01-01 +%s
          946684800

     To convert such an unwieldy number of seconds back to a more
     readable form, use a command like this:

          # local time zone used
          date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
          1999-12-31 19:00:00 -0500

     Or if you do not mind depending on the `@' feature present since
     coreutils 5.3.0, you could shorten this to:

          date -d @946684800 +"%F %T %z"
          1999-12-31 19:00:00 -0500

     Often it is better to output UTC-relative date and time:

          date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
          2000-01-01 00:00:00 +0000



File: coreutils.info,  Node: uname invocation,  Next: hostname invocation,  Prev: date invocation,  Up: System context

21.2 `uname': Print system information
======================================

`uname' prints information about the machine and operating system it is
run on.  If no options are given, `uname' acts as if the `-s' option
were given.  Synopsis:

     uname [OPTION]...

   If multiple options or `-a' are given, the selected information is
printed in this order:

     KERNEL-NAME NODENAME KERNEL-RELEASE KERNEL-VERSION
     MACHINE PROCESSOR HARDWARE-PLATFORM OPERATING-SYSTEM

   The information may contain internal spaces, so such output cannot be
parsed reliably.  In the following example, RELEASE is
`2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001':

     uname -a
     => Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux

   The program accepts the following options.  Also see *Note Common
options::.

`-a'
`--all'
     Print all of the below information, except omit the processor type
     and the hardware platform name if they are unknown.

`-i'
`--hardware-platform'
     Print the hardware platform name (sometimes called the hardware
     implementation).  Print `unknown' if the kernel does not make this
     information easily available, as is the case with Linux kernels.

`-m'
`--machine'
     Print the machine hardware name (sometimes called the hardware
     class or hardware type).

`-n'
`--nodename'
     Print the network node hostname.

`-p'
`--processor'
     Print the processor type (sometimes called the instruction set
     architecture or ISA).  Print `unknown' if the kernel does not make
     this information easily available, as is the case with Linux
     kernels.

`-o'
`--operating-system'
     Print the name of the operating system.

`-r'
`--kernel-release'
     Print the kernel release.

`-s'
`--kernel-name'
     Print the kernel name.  POSIX 1003.1-2001 (*note Standards
     conformance::) calls this "the implementation of the operating
     system", because the POSIX specification itself has no notion of
     "kernel".  The kernel name might be the same as the operating
     system name printed by the `-o' or `--operating-system' option,
     but it might differ.  Some operating systems (e.g., FreeBSD,
     HP-UX) have the same name as their underlying kernels; others
     (e.g., GNU/Linux, Solaris) do not.

`-v'
`--kernel-version'
     Print the kernel version.


   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: hostname invocation,  Next: hostid invocation,  Prev: uname invocation,  Up: System context

21.3 `hostname': Print or set system name
=========================================

With no arguments, `hostname' prints the name of the current host
system.  With one argument, it sets the current host name to the
specified string.  You must have appropriate privileges to set the host
name.  Synopsis:

     hostname [NAME]

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: hostid invocation,  Prev: hostname invocation,  Up: System context

21.4 `hostid': Print numeric host identifier.
=============================================

`hostid' prints the numeric identifier of the current host in
hexadecimal.  This command accepts no arguments.  The only options are
`--help' and `--version'.  *Note Common options::.

   For example, here's what it prints on one system I use:

     $ hostid
     1bac013d

   On that system, the 32-bit quantity happens to be closely related to
the system's Internet address, but that isn't always the case.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Modified command invocation,  Next: Process control,  Prev: System context,  Up: Top

22 Modified command invocation
******************************

This section describes commands that run other commands in some context
different than the current one: a modified environment, as a different
user, etc.

* Menu:

* chroot invocation::           Modify the root directory.
* env invocation::              Modify environment variables.
* nice invocation::             Modify niceness.
* nohup invocation::            Immunize to hangups.
* su invocation::               Modify user and group ID.


File: coreutils.info,  Node: chroot invocation,  Next: env invocation,  Up: Modified command invocation

22.1 `chroot': Run a command with a different root directory
============================================================

`chroot' runs a command with a specified root directory.  On many
systems, only the super-user can do this.  Synopses:

     chroot NEWROOT [COMMAND [ARGS]...]
     chroot OPTION

   Ordinarily, file names are looked up starting at the root of the
directory structure, i.e., `/'.  `chroot' changes the root to the
directory NEWROOT (which must exist) and then runs COMMAND with
optional ARGS.  If COMMAND is not specified, the default is the value
of the `SHELL' environment variable or `/bin/sh' if not set, invoked
with the `-i' option.  COMMAND must not be a special built-in utility
(*note Special built-in utilities::).

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   Here are a few tips to help avoid common problems in using chroot.
To start with a simple example, make COMMAND refer to a statically
linked binary.  If you were to use a dynamically linked executable, then
you'd have to arrange to have the shared libraries in the right place
under your new root directory.

   For example, if you create a statically linked `ls' executable, and
put it in `/tmp/empty', you can run this command as root:

     $ chroot /tmp/empty /ls -Rl /

   Then you'll see output like this:

     /:
     total 1023
     -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls

   If you want to use a dynamically linked executable, say `bash', then
first run `ldd bash' to see what shared objects it needs.  Then, in
addition to copying the actual binary, also copy the listed files to
the required positions under your intended new root directory.
Finally, if the executable requires any other files (e.g., data, state,
device files), copy them into place, too.

   Exit status:

     1   if `chroot' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise


File: coreutils.info,  Node: env invocation,  Next: nice invocation,  Prev: chroot invocation,  Up: Modified command invocation

22.2 `env': Run a command in a modified environment
===================================================

`env' runs a command with a modified environment.  Synopses:

     env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...]
     env

   Operands of the form `VARIABLE=VALUE' set the environment variable
VARIABLE to value VALUE.  VALUE may be empty (`VARIABLE=').  Setting a
variable to an empty value is different from unsetting it.  These
operands are evaluated left-to-right, so if two operands mention the
same variable the earlier is ignored.

   Environment variable names can be empty, and can contain any
characters other than `=' and the null character (ASCII NUL).  However,
it is wise to limit yourself to names that consist solely of
underscores, digits, and ASCII letters, and that begin with a
non-digit, as applications like the shell do not work well with other
names.

   The first operand that does not contain the character `=' specifies
the program to invoke; it is searched for according to the `PATH'
environment variable.  Any remaining arguments are passed as arguments
to that program.  The program should not be a special built-in utility
(*note Special built-in utilities::).

   If no command name is specified following the environment
specifications, the resulting environment is printed.  This is like
specifying the `printenv' program.

   The program accepts the following options.  Also see *Note Common
options::.  Options must precede operands.

`-u NAME'
`--unset=NAME'
     Remove variable NAME from the environment, if it was in the
     environment.

`-'
`-i'
`--ignore-environment'
     Start with an empty environment, ignoring the inherited
     environment.


   Exit status:

     0   if no COMMAND is specified and the environment is output
     1   if `env' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise


File: coreutils.info,  Node: nice invocation,  Next: nohup invocation,  Prev: env invocation,  Up: Modified command invocation

22.3 `nice': Run a command with modified niceness
=================================================

`nice' prints or modifies a process's "niceness", a parameter that
affects whether the process is scheduled favorably.  Synopsis:

     nice [OPTION]... [COMMAND [ARG]...]

   If no arguments are given, `nice' prints the current niceness.
Otherwise, `nice' runs the given COMMAND with its niceness adjusted.
By default, its niceness is incremented by 10.

   Nicenesses range at least from -20 (resulting in the most favorable
scheduling) through 19 (the least favorable).  Some systems may have a
wider range of nicenesses; conversely, other systems may enforce more
restrictive limits.  An attempt to set the niceness outside the
supported range is treated as an attempt to use the minimum or maximum
supported value.

   A niceness should not be confused with a scheduling priority, which
lets applications determine the order in which threads are scheduled to
run.  Unlike a priority, a niceness is merely advice to the scheduler,
which the scheduler is free to ignore.  Also, as a point of
terminology, POSIX defines the behavior of `nice' in terms of a "nice
value", which is the nonnegative difference between a niceness and the
minimum niceness.  Though `nice' conforms to POSIX, its documentation
and diagnostics use the term "niceness" for compatibility with
historical practice.

   COMMAND must not be a special built-in utility (*note Special
built-in utilities::).

   Because many shells have a built-in `nice' command, using an
unadorned `nice' in a script or interactively may get you different
functionality than that described here.

   The program accepts the following option.  Also see *Note Common
options::.  Options must precede operands.

`-n ADJUSTMENT'
`--adjustment=ADJUSTMENT'
     Add ADJUSTMENT instead of 10 to the command's niceness.  If
     ADJUSTMENT is negative and you lack appropriate privileges, `nice'
     issues a warning but otherwise acts as if you specified a zero
     adjustment.

     For compatibility `nice' also supports an obsolete option syntax
     `-ADJUSTMENT'.  New scripts should use `-n ADJUSTMENT' instead.


   Exit status:

     0   if no COMMAND is specified and the niceness is output
     1   if `nice' itself fails
     126 if COMMAND is found but cannot be invoked
     127 if COMMAND cannot be found
     the exit status of COMMAND otherwise

   It is sometimes useful to run a non-interactive program with reduced
niceness.

     $ nice factor 4611686018427387903

   Since `nice' prints the current niceness, you can invoke it through
itself to demonstrate how it works.

   The default behavior is to increase the niceness by `10':

     $ nice
     0
     $ nice nice
     10
     $ nice -n 10 nice
     10

   The ADJUSTMENT is relative to the current niceness.  In the next
example, the first `nice' invocation runs the second one with niceness
10, and it in turn runs the final one with a niceness that is 3 more:

     $ nice nice -n 3 nice
     13

   Specifying a niceness larger than the supported range is the same as
specifying the maximum supported value:

     $ nice -n 10000000000 nice
     19

   Only a privileged user may run a process with lower niceness:

     $ nice -n -1 nice
     nice: cannot set niceness: Permission denied
     0
     $ sudo nice -n -1 nice
     -1


File: coreutils.info,  Node: nohup invocation,  Next: su invocation,  Prev: nice invocation,  Up: Modified command invocation

22.4 `nohup': Run a command immune to hangups
=============================================

`nohup' runs the given COMMAND with hangup signals ignored, so that the
command can continue running in the background after you log out.
Synopsis:

     nohup COMMAND [ARG]...

   If standard input is a terminal, it is redirected from `/dev/null'
so that terminal sessions do not mistakenly consider the terminal to be
used by the command.  This is a GNU extension; programs intended to be
portable to non-GNU hosts should use `nohup COMMAND [ARG]... </dev/null'
instead.

   If standard output is a terminal, the command's standard output is
appended to the file `nohup.out'; if that cannot be written to, it is
appended to the file `$HOME/nohup.out'; and if that cannot be written
to, the command is not run.  Any `nohup.out' or `$HOME/nohup.out' file
created by `nohup' is made readable and writable only to the user,
regardless of the current umask settings.

   If standard error is a terminal, it is normally redirected to the
same file descriptor as the (possibly-redirected) standard output.
However, if standard output is closed, standard error terminal output
is instead appended to the file `nohup.out' or `$HOME/nohup.out' as
above.

   `nohup' does not automatically put the command it runs in the
background; you must do that explicitly, by ending the command line
with an `&'.  Also, `nohup' does not alter the niceness of COMMAND; use
`nice' for that, e.g., `nohup nice COMMAND'.

   COMMAND must not be a special built-in utility (*note Special
built-in utilities::).

   The only options are `--help' and `--version'.  *Note Common
options::.  Options must precede operands.

   Exit status:

     126 if COMMAND is found but cannot be invoked
     127 if `nohup' itself fails or if COMMAND cannot be found
     the exit status of COMMAND otherwise


File: coreutils.info,  Node: su invocation,  Prev: nohup invocation,  Up: Modified command invocation

22.5 `su': Run a command with substitute user and group ID
==========================================================

`su' allows one user to temporarily become another user.  It runs a
command (often an interactive shell) with the real and effective user
ID, group ID, and supplemental groups of a given USER.  Synopsis:

     su [OPTION]... [USER [ARG]...]

   If no USER is given, the default is `root', the super-user.  The
shell to use is taken from USER's `passwd' entry, or `/bin/sh' if none
is specified there.  If USER has a password, `su' prompts for the
password unless run by a user with effective user ID of zero (the
super-user).

   By default, `su' does not change the current directory.  It sets the
environment variables `HOME' and `SHELL' from the password entry for
USER, and if USER is not the super-user, sets `USER' and `LOGNAME' to
USER.  By default, the shell is not a login shell.

   Any additional ARGs are passed as additional arguments to the shell.

   GNU `su' does not treat `/bin/sh' or any other shells specially
(e.g., by setting `argv[0]' to `-su', passing `-c' only to certain
shells, etc.).

   `su' can optionally be compiled to use `syslog' to report failed,
and optionally successful, `su' attempts.  (If the system supports
`syslog'.)  However, GNU `su' does not check if the user is a member of
the `wheel' group; see below.

   The program accepts the following options.  Also see *Note Common
options::.

`-c COMMAND'
`--command=COMMAND'
     Pass COMMAND, a single command line to run, to the shell with a
     `-c' option instead of starting an interactive shell.

`-f'
`--fast'
     Pass the `-f' option to the shell.  This probably only makes sense
     if the shell run is `csh' or `tcsh', for which the `-f' option
     prevents reading the startup file (`.cshrc').  With Bourne-like
     shells, the `-f' option disables file name pattern expansion
     (globbing), which is not likely to be useful.

`-'
`-l'
`--login'
     Make the shell a login shell.  This means the following.  Unset all
     environment variables except `TERM', `HOME', and `SHELL' (which
     are set as described above), and `USER' and `LOGNAME' (which are
     set, even for the super-user, as described above), and set `PATH'
     to a compiled-in default value.  Change to USER's home directory.
     Prepend `-' to the shell's name, intended to make it read its
     login startup file(s).

`-m'
`-p'
`--preserve-environment'
     Do not change the environment variables `HOME', `USER', `LOGNAME',
     or `SHELL'.  Run the shell given in the environment variable
     `SHELL' instead of the shell from USER's passwd entry, unless the
     user running `su' is not the super-user and USER's shell is
     restricted.  A "restricted shell" is one that is not listed in the
     file `/etc/shells', or in a compiled-in list if that file does not
     exist.  Parts of what this option does can be overridden by
     `--login' and `--shell'.

`-s SHELL'
`--shell=SHELL'
     Run SHELL instead of the shell from USER's passwd entry, unless
     the user running `su' is not the super-user and USER's shell is
     restricted (see `-m' just above).


   Exit status:

     1   if `su' itself fails
     126 if subshell is found but cannot be invoked
     127 if subshell cannot be found
     the exit status of the subshell otherwise

22.5.1 Why GNU `su' does not support the `wheel' group
------------------------------------------------------

(This section is by Richard Stallman.)

   Sometimes a few of the users try to hold total power over all the
rest.  For example, in 1984, a few users at the MIT AI lab decided to
seize power by changing the operator password on the Twenex system and
keeping it secret from everyone else.  (I was able to thwart this coup
and give power back to the users by patching the kernel, but I wouldn't
know how to do that in Unix.)

   However, occasionally the rulers do tell someone.  Under the usual
`su' mechanism, once someone learns the root password who sympathizes
with the ordinary users, he or she can tell the rest.  The "wheel
group" feature would make this impossible, and thus cement the power of
the rulers.

   I'm on the side of the masses, not that of the rulers.  If you are
used to supporting the bosses and sysadmins in whatever they do, you
might find this idea strange at first.


File: coreutils.info,  Node: Process control,  Next: Delaying,  Prev: Modified command invocation,  Up: Top

23 Process control
******************

* Menu:

* kill invocation::             Sending a signal to processes.


File: coreutils.info,  Node: kill invocation,  Up: Process control

23.1 `kill': Send a signal to processes
=======================================

The `kill' command sends a signal to processes, causing them to
terminate or otherwise act upon receiving the signal in some way.
Alternatively, it lists information about signals.  Synopses:

     kill [-s SIGNAL | --signal SIGNAL | -SIGNAL] PID...
     kill [-l | --list | -t | --table] [SIGNAL]...

   The first form of the `kill' command sends a signal to all PID
arguments.  The default signal to send if none is specified is `TERM'.
The special signal number `0' does not denote a valid signal, but can
be used to test whether the PID arguments specify processes to which a
signal could be sent.

   If PID is positive, the signal is sent to the process with the
process ID PID.  If PID is zero, the signal is sent to all processes in
the process group of the current process.  If PID is -1, the signal is
sent to all processes for which the user has permission to send a
signal.  If PID is less than -1, the signal is sent to all processes in
the process group that equals the absolute value of PID.

   If PID is not positive, a system-dependent set of system processes
is excluded from the list of processes to which the signal is sent.

   If a negative PID argument is desired as the first one, it should be
preceded by `--'.  However, as a common extension to POSIX, `--' is not
required with `kill -SIGNAL -PID'.  The following commands are
equivalent:

     kill -15 -1
     kill -TERM -1
     kill -s TERM -- -1
     kill -- -1

   The first form of the `kill' command succeeds if every PID argument
specifies at least one process that the signal was sent to.

   The second form of the `kill' command lists signal information.
Either the `-l' or `--list' option, or the `-t' or `--table' option
must be specified.  Without any SIGNAL argument, all supported signals
are listed.  The output of `-l' or `--list' is a list of the signal
names, one per line; if SIGNAL is already a name, the signal number is
printed instead.  The output of `-t' or `--table' is a table of signal
numbers, names, and descriptions.  This form of the `kill' command
succeeds if all SIGNAL arguments are valid and if there is no output
error.

   The `kill' command also supports the `--help' and `--version'
options.  *Note Common options::.

   A SIGNAL may be a signal name like `HUP', or a signal number like
`1', or an exit status of a process terminated by the signal.  A signal
name can be given in canonical form or prefixed by `SIG'.  The case of
the letters is ignored, except for the `-SIGNAL' option which must use
upper case to avoid ambiguity with lower case option letters.  The
following signal names and numbers are supported on all POSIX compliant
systems:

`HUP'
     1.  Hangup.

`INT'
     2.  Terminal interrupt.

`QUIT'
     3.  Terminal quit.

`ABRT'
     6.  Process abort.

`KILL'
     9.  Kill (cannot be caught or ignored).

`ALRM'
     14.  Alarm Clock.

`TERM'
     15.  Termination.

Other supported signal names have system-dependent corresponding
numbers.  All systems conforming to POSIX 1003.1-2001 also support the
following signals:

`BUS'
     Access to an undefined portion of a memory object.

`CHLD'
     Child process terminated, stopped, or continued.

`CONT'
     Continue executing, if stopped.

`FPE'
     Erroneous arithmetic operation.

`ILL'
     Illegal Instruction.

`PIPE'
     Write on a pipe with no one to read it.

`SEGV'
     Invalid memory reference.

`STOP'
     Stop executing (cannot be caught or ignored).

`TSTP'
     Terminal stop.

`TTIN'
     Background process attempting read.

`TTOU'
     Background process attempting write.

`URG'
     High bandwidth data is available at a socket.

`USR1'
     User-defined signal 1.

`USR2'
     User-defined signal 2.

POSIX 1003.1-2001 systems that support the XSI extension also support
the following signals:

`POLL'
     Pollable event.

`PROF'
     Profiling timer expired.

`SYS'
     Bad system call.

`TRAP'
     Trace/breakpoint trap.

`VTALRM'
     Virtual timer expired.

`XCPU'
     CPU time limit exceeded.

`XFSZ'
     File size limit exceeded.

POSIX 1003.1-2001 systems that support the XRT extension also support
at least eight real-time signals called `RTMIN', `RTMIN+1', ...,
`RTMAX-1', `RTMAX'.


File: coreutils.info,  Node: Delaying,  Next: Numeric operations,  Prev: Process control,  Up: Top

24 Delaying
***********

* Menu:

* sleep invocation::            Delay for a specified time.


File: coreutils.info,  Node: sleep invocation,  Up: Delaying

24.1 `sleep': Delay for a specified time
========================================

`sleep' pauses for an amount of time specified by the sum of the values
of the command line arguments.  Synopsis:

     sleep NUMBER[smhd]...

   Each argument is a number followed by an optional unit; the default
is seconds.  The units are:

`s'
     seconds

`m'
     minutes

`h'
     hours

`d'
     days

   Historical implementations of `sleep' have required that NUMBER be
an integer, and only accepted a single argument without a suffix.
However, GNU `sleep' accepts arbitrary floating point numbers (using a
period before any fractional digits).

   The only options are `--help' and `--version'.  *Note Common
options::.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: Numeric operations,  Next: File permissions,  Prev: Delaying,  Up: Top

25 Numeric operations
*********************

These programs do numerically-related operations.

* Menu:

* factor invocation::              Show factors of numbers.
* seq invocation::                 Print sequences of numbers.


File: coreutils.info,  Node: factor invocation,  Next: seq invocation,  Up: Numeric operations

25.1 `factor': Print prime factors
==================================

`factor' prints prime factors.  Synopses:

     factor [NUMBER]...
     factor OPTION

   If no NUMBER is specified on the command line, `factor' reads
numbers from standard input, delimited by newlines, tabs, or spaces.

   The only options are `--help' and `--version'.  *Note Common
options::.

   The algorithm it uses is not very sophisticated, so for some inputs
`factor' runs for a long time.  The hardest numbers to factor are the
products of large primes.  Factoring the product of the two largest
32-bit prime numbers takes about 80 seconds of CPU time on a 1.6 GHz
Athlon.

     $ p=`echo '4294967279 * 4294967291'|bc`
     $ factor $p
     18446743979220271189: 4294967279 4294967291

   Similarly, it takes about 80 seconds for GNU factor (from
coreutils-5.1.2) to "factor" the largest 64-bit prime:

     $ factor 18446744073709551557
       18446744073709551557: 18446744073709551557

   In contrast, `factor' factors the largest 64-bit number in just over
a tenth of a second:

     $ factor `echo '2^64-1'|bc`
     18446744073709551615: 3 5 17 257 641 65537 6700417

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: seq invocation,  Prev: factor invocation,  Up: Numeric operations

25.2 `seq': Print numeric sequences
===================================

`seq' prints a sequence of numbers to standard output.  Synopses:

     seq [OPTION]... LAST
     seq [OPTION]... FIRST LAST
     seq [OPTION]... FIRST INCREMENT LAST

   `seq' prints the numbers from FIRST to LAST by INCREMENT.  By
default, each number is printed on a separate line.  When INCREMENT is
not specified, it defaults to `1', even when FIRST is larger than LAST.
FIRST also defaults to `1'.  So `seq 1' prints `1', but `seq 0' and
`seq 10 5' produce no output.  Floating-point numbers may be specified
(using a period before any fractional digits).

   The program accepts the following options.  Also see *Note Common
options::.  Options must precede operands.

`-f FORMAT'
`--format=FORMAT'
     Print all numbers using FORMAT.  FORMAT must contain exactly one
     of the `printf'-style floating point conversion specifications
     `%a', `%e', `%f', `%g', `%A', `%E', `%F', `%G'.  The `%' may be
     followed by zero or more flags taken from the set `-+#0 '', then
     an optional width containing one or more digits, then an optional
     precision consisting of a `.' followed by zero or more digits.
     FORMAT may also contain any number of `%%' conversion
     specifications.  All conversion specifications have the same
     meaning as with `printf'.

     The default format is derived from FIRST, STEP, and LAST.  If
     these all use a fixed point decimal representation, the default
     format is `%.Pf', where P is the minimum precision that can
     represent the output numbers exactly.  Otherwise, the default
     format is `%g'.

`-s STRING'
`--separator=STRING'
     Separate numbers with STRING; default is a newline.  The output
     always terminates with a newline.

`-w'
`--equal-width'
     Print all numbers with the same width, by padding with leading
     zeros.  FIRST, STEP, and LAST should all use a fixed point decimal
     representation.  (To have other kinds of padding, use `--format').


   You can get finer-grained control over output with `-f':

     $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
     (-9.00E+05)
     ( 2.00E+05)
     ( 1.30E+06)

   If you want hexadecimal integer output, you can use `printf' to
perform the conversion:

     $ printf '%x\n' `seq 1048575 1024 1050623`
     fffff
     1003ff
     1007ff

   For very long lists of numbers, use xargs to avoid system
limitations on the length of an argument list:

     $ seq 1000000 | xargs printf '%x\n' | tail -n 3
     f423e
     f423f
     f4240

   To generate octal output, use the printf `%o' format instead of `%x'.

   On most systems, seq can produce whole-number output for values up to
at least `2^53'.  Larger integers are approximated.  The details differ
depending on your floating-point implementation, but a common case is
that `seq' works with integers through `2^64', and larger integers may
not be numerically correct:

     $ seq 18446744073709551616 1 18446744073709551618
     18446744073709551616
     18446744073709551616
     18446744073709551618

   Be careful when using `seq' with a fractional INCREMENT; otherwise
you may see surprising results.  Most people would expect to see
`0.000003' printed as the last number in this example:

     $ seq -s ' ' 0 0.000001 0.000003
     0.000000 0.000001 0.000002

   But that doesn't happen on many systems because `seq' is implemented
using binary floating point arithmetic (via the C `long double'
type)--which means decimal fractions like `0.000001' cannot be
represented exactly.  That in turn means some nonintuitive conditions
like `0.000001 * 3 > 0.000003' will end up being true.

   To work around that in the above example, use a slightly larger
number as the LAST value:

     $ seq -s ' ' 0 0.000001 0.0000031
     0.000000 0.000001 0.000002 0.000003

   In general, when using an INCREMENT with a fractional part, where
(LAST - FIRST) / INCREMENT is (mathematically) a whole number, specify
a slightly larger (or smaller, if INCREMENT is negative) value for LAST
to ensure that LAST is the final value printed by seq.

   An exit status of zero indicates success, and a nonzero value
indicates failure.


File: coreutils.info,  Node: File permissions,  Next: Date input formats,  Prev: Numeric operations,  Up: Top

26 File permissions
*******************

Each file has a set of "file mode bits" that control the kinds of
access that users have to that file.  They can be represented either in
symbolic form or as an octal number.

* Menu:

* Mode Structure::              Structure of file mode bits.
* Symbolic Modes::              Mnemonic representation of file mode bits.
* Numeric Modes::               File mode bits as octal numbers.
* Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.


File: coreutils.info,  Node: Mode Structure,  Next: Symbolic Modes,  Up: File permissions

26.1 Structure of File Mode Bits
================================

The file mode bits have two parts: the "file permission bits", which
control ordinary access to the file, and "special mode bits", which
affect only some files.

   There are three kinds of permissions that a user can have for a file:

  1. permission to read the file.  For directories, this means
     permission to list the contents of the directory.

  2. permission to write to (change) the file.  For directories, this
     means permission to create and remove files in the directory.

  3. permission to execute the file (run it as a program).  For
     directories, this means permission to access files in the
     directory.

   There are three categories of users who may have different
permissions to perform any of the above operations on a file:

  1. the file's owner;

  2. other users who are in the file's group;

  3. everyone else.

   Files are given an owner and group when they are created.  Usually
the owner is the current user and the group is the group of the
directory the file is in, but this varies with the operating system, the
file system the file is created on, and the way the file is created.
You can change the owner and group of a file by using the `chown' and
`chgrp' commands.

   In addition to the three sets of three permissions listed above, the
file mode bits have three special components, which affect only
executable files (programs) and, on most systems, directories:

  1. Set the process's effective user ID to that of the file upon
     execution (called the "set-user-ID bit", or sometimes the "setuid
     bit").  For directories on a few systems, give files created in
     the directory the same owner as the directory, no matter who
     creates them, and set the set-user-ID bit of newly-created
     subdirectories.

  2. Set the process's effective group ID to that of the file upon
     execution (called the "set-group-ID bit", or sometimes the "setgid
     bit").  For directories on most systems, give files created in the
     directory the same group as the directory, no matter what group
     the user who creates them is in, and set the set-group-ID bit of
     newly-created subdirectories.

  3. Prevent unprivileged users from removing or renaming a file in a
     directory unless they own the file or the directory; this is
     called the "restricted deletion flag" for the directory, and is
     commonly found on world-writable directories like `/tmp'.

     For regular files on some older systems, save the program's text
     image on the swap device so it will load more quickly when run;
     this is called the "sticky bit".

   In addition to the file mode bits listed above, there may be file
attributes specific to the file system, e.g., access control lists
(ACLs), whether a file is compressed, whether a file can be modified
(immutability), and whether a file can be dumped.  These are usually
set using programs specific to the file system.  For example:

ext2
     On GNU and GNU/Linux the file attributes specific to the ext2 file
     system are set using `chattr'.

FFS
     On FreeBSD the file flags specific to the FFS file system are set
     using `chflags'.

   Even if a file's mode bits allow an operation on that file, that
operation may still fail, because:

   * the file-system-specific attributes or flags do not permit it; or

   * the file system is mounted as read-only.

   For example, if the immutable attribute is set on a file, it cannot
be modified, regardless of the fact that you may have just run `chmod
a+w FILE'.


File: coreutils.info,  Node: Symbolic Modes,  Next: Numeric Modes,  Prev: Mode Structure,  Up: File permissions

26.2 Symbolic Modes
===================

"Symbolic modes" represent changes to files' mode bits as operations on
single-character symbols.  They allow you to modify either all or
selected parts of files' mode bits, optionally based on their previous
values, and perhaps on the current `umask' as well (*note Umask and
Protection::).

   The format of symbolic modes is:

     [ugoa...][+-=]PERMS...[,...]

where PERMS is either zero or more letters from the set `rwxXst', or a
single letter from the set `ugo'.

   The following sections describe the operators and other details of
symbolic modes.

* Menu:

* Setting Permissions::          Basic operations on permissions.
* Copying Permissions::          Copying existing permissions.
* Changing Special Mode Bits::   Special mode bits.
* Conditional Executability::    Conditionally affecting executability.
* Multiple Changes::             Making multiple changes.
* Umask and Protection::              The effect of the umask.


File: coreutils.info,  Node: Setting Permissions,  Next: Copying Permissions,  Up: Symbolic Modes

26.2.1 Setting Permissions
--------------------------

The basic symbolic operations on a file's permissions are adding,
removing, and setting the permission that certain users have to read,
write, and execute or search the file.  These operations have the
following format:

     USERS OPERATION PERMISSIONS

The spaces between the three parts above are shown for readability only;
symbolic modes cannot contain spaces.

   The USERS part tells which users' access to the file is changed.  It
consists of one or more of the following letters (or it can be empty;
*note Umask and Protection::, for a description of what happens then).
When more than one of these letters is given, the order that they are
in does not matter.

`u'
     the user who owns the file;

`g'
     other users who are in the file's group;

`o'
     all other users;

`a'
     all users; the same as `ugo'.

   The OPERATION part tells how to change the affected users' access to
the file, and is one of the following symbols:

`+'
     to add the PERMISSIONS to whatever permissions the USERS already
     have for the file;

`-'
     to remove the PERMISSIONS from whatever permissions the USERS
     already have for the file;

`='
     to make the PERMISSIONS the only permissions that the USERS have
     for the file.

   The PERMISSIONS part tells what kind of access to the file should be
changed; it is normally zero or more of the following letters.  As with
the USERS part, the order does not matter when more than one letter is
given.  Omitting the PERMISSIONS part is useful only with the `='
operation, where it gives the specified USERS no access at all to the
file.

`r'
     the permission the USERS have to read the file;

`w'
     the permission the USERS have to write to the file;

`x'
     the permission the USERS have to execute the file, or search it if
     it is a directory.

   For example, to give everyone permission to read and write a regular
file, but not to execute it, use:

     a=rw

   To remove write permission for all users other than the file's
owner, use:

     go-w

The above command does not affect the access that the owner of the file
has to it, nor does it affect whether other users can read or execute
the file.

   To give everyone except a file's owner no permission to do anything
with that file, use the mode below.  Other users could still remove the
file, if they have write permission on the directory it is in.

     go=

Another way to specify the same thing is:

     og-rwx


File: coreutils.info,  Node: Copying Permissions,  Next: Changing Special Mode Bits,  Prev: Setting Permissions,  Up: Symbolic Modes

26.2.2 Copying Existing Permissions
-----------------------------------

You can base a file's permissions on its existing permissions.  To do
this, instead of using a series of `r', `w', or `x' letters after the
operator, you use the letter `u', `g', or `o'.  For example, the mode

     o+g

adds the permissions for users who are in a file's group to the
permissions that other users have for the file.  Thus, if the file
started out as mode 664 (`rw-rw-r--'), the above mode would change it
to mode 666 (`rw-rw-rw-').  If the file had started out as mode 741
(`rwxr----x'), the above mode would change it to mode 745
(`rwxr--r-x').  The `-' and `=' operations work analogously.


File: coreutils.info,  Node: Changing Special Mode Bits,  Next: Conditional Executability,  Prev: Copying Permissions,  Up: Symbolic Modes

26.2.3 Changing Special Mode Bits
---------------------------------

In addition to changing a file's read, write, and execute/search
permissions, you can change its special mode bits.  *Note Mode
Structure::, for a summary of these special mode bits.

   To change the file mode bits to set the user ID on execution, use
`u' in the USERS part of the symbolic mode and `s' in the PERMISSIONS
part.

   To change the file mode bits to set the group ID on execution, use
`g' in the USERS part of the symbolic mode and `s' in the PERMISSIONS
part.

   To set both user and group ID on execution, omit the USERS part of
the symbolic mode (or use `a') and use `s' in the PERMISSIONS part.

   To change the file mode bits to set the restricted deletion flag or
sticky bit, omit the USERS part of the symbolic mode (or use `a') and
use `t' in the PERMISSIONS part.

   For example, to set the set-user-ID mode bit of a program, you can
use the mode:

     u+s

   To remove both set-user-ID and set-group-ID mode bits from it, you
can use the mode:

     a-s

   To set the restricted deletion flag or sticky bit, you can use the
mode:

     +t

   The combination `o+s' has no effect.  On GNU systems the
combinations `u+t' and `g+t' have no effect, and `o+t' acts like plain
`+t'.

   The `=' operator is not very useful with special mode bits.  For
example, the mode:

     o=t

does set the restricted deletion flag or sticky bit, but it also
removes all read, write, and execute/search permissions that users not
in the file's group might have had for it.

   *Note Directory Setuid and Setgid::, for additional rules concerning
set-user-ID and set-group-ID bits and directories.


File: coreutils.info,  Node: Conditional Executability,  Next: Multiple Changes,  Prev: Changing Special Mode Bits,  Up: Symbolic Modes

26.2.4 Conditional Executability
--------------------------------

There is one more special type of symbolic permission: if you use `X'
instead of `x', execute/search permission is affected only if the file
is a directory or already had execute permission.

   For example, this mode:

     a+X

gives all users permission to search directories, or to execute files if
anyone could execute them before.


File: coreutils.info,  Node: Multiple Changes,  Next: Umask and Protection,  Prev: Conditional Executability,  Up: Symbolic Modes

26.2.5 Making Multiple Changes
------------------------------

The format of symbolic modes is actually more complex than described
above (*note Setting Permissions::).  It provides two ways to make
multiple changes to files' mode bits.

   The first way is to specify multiple OPERATION and PERMISSIONS parts
after a USERS part in the symbolic mode.

   For example, the mode:

     og+rX-w

gives users other than the owner of the file read permission and, if it
is a directory or if someone already had execute permission to it,
gives them execute/search permission; and it also denies them write
permission to the file.  It does not affect the permission that the
owner of the file has for it.  The above mode is equivalent to the two
modes:

     og+rX
     og-w

   The second way to make multiple changes is to specify more than one
simple symbolic mode, separated by commas.  For example, the mode:

     a+r,go-w

gives everyone permission to read the file and removes write permission
on it for all users except its owner.  Another example:

     u=rwx,g=rx,o=

sets all of the permission bits for the file explicitly.  (It gives
users who are not in the file's group no permission at all for it.)

   The two methods can be combined.  The mode:

     a+r,g+x-w

gives all users permission to read the file, and gives users who are in
the file's group permission to execute/search it as well, but not
permission to write to it.  The above mode could be written in several
different ways; another is:

     u+r,g+rx,o+r,g-w


File: coreutils.info,  Node: Umask and Protection,  Prev: Multiple Changes,  Up: Symbolic Modes

26.2.6 The Umask and Protection
-------------------------------

If the USERS part of a symbolic mode is omitted, it defaults to `a'
(affect all users), except that any permissions that are _set_ in the
system variable `umask' are _not affected_.  The value of `umask' can
be set using the `umask' command.  Its default value varies from system
to system.

   Omitting the USERS part of a symbolic mode is generally not useful
with operations other than `+'.  It is useful with `+' because it
allows you to use `umask' as an easily customizable protection against
giving away more permission to files than you intended to.

   As an example, if `umask' has the value 2, which removes write
permission for users who are not in the file's group, then the mode:

     +w

adds permission to write to the file to its owner and to other users who
are in the file's group, but _not_ to other users.  In contrast, the
mode:

     a+w

ignores `umask', and _does_ give write permission for the file to all
users.


File: coreutils.info,  Node: Numeric Modes,  Next: Directory Setuid and Setgid,  Prev: Symbolic Modes,  Up: File permissions

26.3 Numeric Modes
==================

As an alternative to giving a symbolic mode, you can give an octal
(base 8) number that represents the mode.  This number is always
interpreted in octal; you do not have to add a leading `0', as you do
in C.  Mode `0055' is the same as mode `55'.

   A numeric mode is usually shorter than the corresponding symbolic
mode, but it is limited in that normally it cannot take into account the
previous file mode bits; it can only set them absolutely.  (As
discussed in the next section, the set-user-ID and set-group-ID bits of
directories are an exception to this general limitation.)

   The permissions granted to the user, to other users in the file's
group, and to other users not in the file's group each require three
bits, which are represented as one octal digit.  The three special mode
bits also require one bit each, and they are as a group represented as
another octal digit.  Here is how the bits are arranged, starting with
the lowest valued bit:

     Value in  Corresponding
     Mode      Mode Bit

               Other users not in the file's group:
        1      Execute/search
        2      Write
        4      Read

               Other users in the file's group:
       10      Execute/search
       20      Write
       40      Read

               The file's owner:
      100      Execute/search
      200      Write
      400      Read

               Special mode bits:
     1000      Restricted deletion flag or sticky bit
     2000      Set group ID on execution
     4000      Set user ID on execution

   For example, numeric mode `4755' corresponds to symbolic mode
`u=rwxs,go=rx', and numeric mode `664' corresponds to symbolic mode
`ug=rw,o=r'.  Numeric mode `0' corresponds to symbolic mode `a='.


File: coreutils.info,  Node: Directory Setuid and Setgid,  Prev: Numeric Modes,  Up: File permissions

26.4 Directories and the Set-User-ID and Set-Group-ID Bits
==========================================================

On most systems, if a directory's set-group-ID bit is set, newly
created subfiles inherit the same group as the directory, and newly
created subdirectories inherit the set-group-ID bit of the parent
directory.  On a few systems, a directory's set-user-ID bit has a
similar effect on the ownership of new subfiles and the set-user-ID
bits of new subdirectories.  These mechanisms let users share files
more easily, by lessening the need to use `chmod' or `chown' to share
new files.

   These convenience mechanisms rely on the set-user-ID and set-group-ID
bits of directories.  If commands like `chmod' and `mkdir' routinely
cleared these bits on directories, the mechanisms would be less
convenient and it would be harder to share files.  Therefore, a command
like `chmod' does not affect the set-user-ID or set-group-ID bits of a
directory unless the user specifically mentions them in a symbolic
mode, or sets them in a numeric mode.  For example, on systems that
support set-group-ID inheritance:

     # These commands leave the set-user-ID and
     # set-group-ID bits of the subdirectories alone,
     # so that they retain their default values.
     mkdir A B C
     chmod 755 A
     chmod 0755 B
     chmod u=rwx,go=rx C
     mkdir -m 755 D
     mkdir -m 0755 E
     mkdir -m u=rwx,go=rx F

   If you want to try to set these bits, you must mention them
explicitly in the symbolic or numeric modes, e.g.:

     # These commands try to set the set-user-ID
     # and set-group-ID bits of the subdirectories.
     mkdir G H
     chmod 6755 G
     chmod u=rwx,go=rx,a+s H
     mkdir -m 6755 I
     mkdir -m u=rwx,go=rx,a+s J

   If you want to try to clear these bits, you must mention them
explicitly in a symbolic mode, e.g.:

     # This command tries to clear the set-user-ID
     # and set-group-ID bits of the directory D.
     chmod a-s D

   This behavior is a GNU extension.  Portable scripts should not rely
on requests to set or clear these bits on directories, as POSIX allows
implementations to ignore these requests.


File: coreutils.info,  Node: Date input formats,  Next: Opening the software toolbox,  Prev: File permissions,  Up: Top

27 Date input formats
*********************

First, a quote:

     Our units of temporal measurement, from seconds on up to months,
     are so complicated, asymmetrical and disjunctive so as to make
     coherent mental reckoning in time all but impossible.  Indeed, had
     some tyrannical god contrived to enslave our minds to time, to
     make it all but impossible for us to escape subjection to sodden
     routines and unpleasant surprises, he could hardly have done
     better than handing down our present system.  It is like a set of
     trapezoidal building blocks, with no vertical or horizontal
     surfaces, like a language in which the simplest thought demands
     ornate constructions, useless particles and lengthy
     circumlocutions.  Unlike the more successful patterns of language
     and science, which enable us to face experience boldly or at least
     level-headedly, our system of temporal calculation silently and
     persistently encourages our terror of time.

     ...  It is as though architects had to measure length in feet,
     width in meters and height in ells; as though basic instruction
     manuals demanded a knowledge of five different languages.  It is
     no wonder then that we often look into our own immediate past or
     future, last Tuesday or a week from Sunday, with feelings of
     helpless confusion.  ...

     -- Robert Grudin, `Time and the Art of Living'.

   This section describes the textual date representations that GNU
programs accept.  These are the strings you, as a user, can supply as
arguments to the various programs.  The C interface (via the `get_date'
function) is not described here.

* Menu:

* General date syntax::            Common rules.
* Calendar date items::            19 Dec 1994.
* Time of day items::              9:20pm.
* Time zone items::                EST, PDT, GMT.
* Day of week items::              Monday and others.
* Relative items in date strings:: next tuesday, 2 years ago.
* Pure numbers in date strings::   19931219, 1440.
* Seconds since the Epoch::        @1078100502.
* Specifying time zone rules::     TZ="America/New_York", TZ="UTC0".
* Authors of get_date::            Bellovin, Eggert, Salz, Berets, et al.


File: coreutils.info,  Node: General date syntax,  Next: Calendar date items,  Up: Date input formats

27.1 General date syntax
========================

A "date" is a string, possibly empty, containing many items separated
by whitespace.  The whitespace may be omitted when no ambiguity arises.
The empty string means the beginning of today (i.e., midnight).  Order
of the items is immaterial.  A date string may contain many flavors of
items:

   * calendar date items

   * time of day items

   * time zone items

   * day of the week items

   * relative items

   * pure numbers.

We describe each of these item types in turn, below.

   A few ordinal numbers may be written out in words in some contexts.
This is most useful for specifying day of the week items or relative
items (see below).  Among the most commonly used ordinal numbers, the
word `last' stands for -1, `this' stands for 0, and `first' and `next'
both stand for 1.  Because the word `second' stands for the unit of
time there is no way to write the ordinal number 2, but for convenience
`third' stands for 3, `fourth' for 4, `fifth' for 5, `sixth' for 6,
`seventh' for 7, `eighth' for 8, `ninth' for 9, `tenth' for 10,
`eleventh' for 11 and `twelfth' for 12.

   When a month is written this way, it is still considered to be
written numerically, instead of being "spelled in full"; this changes
the allowed strings.

   In the current implementation, only English is supported for words
and abbreviations like `AM', `DST', `EST', `first', `January',
`Sunday', `tomorrow', and `year'.

   The output of the `date' command is not always acceptable as a date
string, not only because of the language problem, but also because
there is no standard meaning for time zone items like `IST'.  When using
`date' to generate a date string intended to be parsed later, specify a
date format that is independent of language and that does not use time
zone items other than `UTC' and `Z'.  Here are some ways to do this:

     $ LC_ALL=C TZ=UTC0 date
     Mon Mar  1 00:21:42 UTC 2004
     $ TZ=UTC0 date +'%Y-%m-%d %H:%M:%SZ'
     2004-03-01 00:21:42Z
     $ date --iso-8601=ns | tr T ' '  # --iso-8601 is a GNU extension.
     2004-02-29 16:21:42,692722128-0800
     $ date --rfc-2822  # a GNU extension
     Sun, 29 Feb 2004 16:21:42 -0800
     $ date +'%Y-%m-%d %H:%M:%S %z'  # %z is a GNU extension.
     2004-02-29 16:21:42 -0800
     $ date +'@%s.%N'  # %s and %N are GNU extensions.
     @1078100502.692722128

   Alphabetic case is completely ignored in dates.  Comments may be
introduced between round parentheses, as long as included parentheses
are properly nested.  Hyphens not followed by a digit are currently
ignored.  Leading zeros on numbers are ignored.

   Invalid dates like `2005-02-29' or times like `24:00' are rejected.
In the typical case of a host that does not support leap seconds, a
time like `23:59:60' is rejected even if it corresponds to a valid leap
second.


File: coreutils.info,  Node: Calendar date items,  Next: Time of day items,  Prev: General date syntax,  Up: Date input formats

27.2 Calendar date items
========================

A "calendar date item" specifies a day of the year.  It is specified
differently, depending on whether the month is specified numerically or
literally.  All these strings specify the same calendar date:

     1972-09-24     # ISO 8601.
     72-9-24        # Assume 19xx for 69 through 99,
                    # 20xx for 00 through 68.
     72-09-24       # Leading zeros are ignored.
     9/24/72        # Common U.S. writing.
     24 September 1972
     24 Sept 72     # September has a special abbreviation.
     24 Sep 72      # Three-letter abbreviations always allowed.
     Sep 24, 1972
     24-sep-72
     24sep72

   The year can also be omitted.  In this case, the last specified year
is used, or the current year if none.  For example:

     9/24
     sep 24

   Here are the rules.

   For numeric months, the ISO 8601 format `YEAR-MONTH-DAY' is allowed,
where YEAR is any positive number, MONTH is a number between 01 and 12,
and DAY is a number between 01 and 31.  A leading zero must be present
if a number is less than ten.  If YEAR is 68 or smaller, then 2000 is
added to it; otherwise, if YEAR is less than 100, then 1900 is added to
it.  The construct `MONTH/DAY/YEAR', popular in the United States, is
accepted.  Also `MONTH/DAY', omitting the year.

   Literal months may be spelled out in full: `January', `February',
`March', `April', `May', `June', `July', `August', `September',
`October', `November' or `December'.  Literal months may be abbreviated
to their first three letters, possibly followed by an abbreviating dot.
It is also permitted to write `Sept' instead of `September'.

   When months are written literally, the calendar date may be given as
any of the following:

     DAY MONTH YEAR
     DAY MONTH
     MONTH DAY YEAR
     DAY-MONTH-YEAR

   Or, omitting the year:

     MONTH DAY


File: coreutils.info,  Node: Time of day items,  Next: Time zone items,  Prev: Calendar date items,  Up: Date input formats

27.3 Time of day items
======================

A "time of day item" in date strings specifies the time on a given day.
Here are some examples, all of which represent the same time:

     20:02:00.000000
     20:02
     8:02pm
     20:02-0500      # In EST (U.S. Eastern Standard Time).

   More generally, the time of day may be given as
`HOUR:MINUTE:SECOND', where HOUR is a number between 0 and 23, MINUTE
is a number between 0 and 59, and SECOND is a number between 0 and 59
possibly followed by `.' or `,' and a fraction containing one or more
digits.  Alternatively, `:SECOND' can be omitted, in which case it is
taken to be zero.  On the rare hosts that support leap seconds, SECOND
may be 60.

   If the time is followed by `am' or `pm' (or `a.m.' or `p.m.'), HOUR
is restricted to run from 1 to 12, and `:MINUTE' may be omitted (taken
to be zero).  `am' indicates the first half of the day, `pm' indicates
the second half of the day.  In this notation, 12 is the predecessor of
1: midnight is `12am' while noon is `12pm'.  (This is the zero-oriented
interpretation of `12am' and `12pm', as opposed to the old tradition
derived from Latin which uses `12m' for noon and `12pm' for midnight.)

   The time may alternatively be followed by a time zone correction,
expressed as `SHHMM', where S is `+' or `-', HH is a number of zone
hours and MM is a number of zone minutes.  You can also separate HH
from MM with a colon.  When a time zone correction is given this way, it
forces interpretation of the time relative to Coordinated Universal
Time (UTC), overriding any previous specification for the time zone or
the local time zone.  For example, `+0530' and `+05:30' both stand for
the time zone 5.5 hours ahead of UTC (e.g., India).  The MINUTE part of
the time of day may not be elided when a time zone correction is used.
This is the best way to specify a time zone correction by fractional
parts of an hour.

   Either `am'/`pm' or a time zone correction may be specified, but not
both.


File: coreutils.info,  Node: Time zone items,  Next: Day of week items,  Prev: Time of day items,  Up: Date input formats

27.4 Time zone items
====================

A "time zone item" specifies an international time zone, indicated by a
small set of letters, e.g., `UTC' or `Z' for Coordinated Universal
Time.  Any included periods are ignored.  By following a
non-daylight-saving time zone by the string `DST' in a separate word
(that is, separated by some white space), the corresponding daylight
saving time zone may be specified.  Alternatively, a
non-daylight-saving time zone can be followed by a time zone
correction, to add the two values.  This is normally done only for
`UTC'; for example, `UTC+05:30' is equivalent to `+05:30'.

   Time zone items other than `UTC' and `Z' are obsolescent and are not
recommended, because they are ambiguous; for example, `EST' has a
different meaning in Australia than in the United States.  Instead,
it's better to use unambiguous numeric time zone corrections like
`-0500', as described in the previous section.

   If neither a time zone item nor a time zone correction is supplied,
time stamps are interpreted using the rules of the default time zone
(*note Specifying time zone rules::).


File: coreutils.info,  Node: Day of week items,  Next: Relative items in date strings,  Prev: Time zone items,  Up: Date input formats

27.5 Day of week items
======================

The explicit mention of a day of the week will forward the date (only
if necessary) to reach that day of the week in the future.

   Days of the week may be spelled out in full: `Sunday', `Monday',
`Tuesday', `Wednesday', `Thursday', `Friday' or `Saturday'.  Days may
be abbreviated to their first three letters, optionally followed by a
period.  The special abbreviations `Tues' for `Tuesday', `Wednes' for
`Wednesday' and `Thur' or `Thurs' for `Thursday' are also allowed.

   A number may precede a day of the week item to move forward
supplementary weeks.  It is best used in expression like `third
monday'.  In this context, `last DAY' or `next DAY' is also acceptable;
they move one week before or after the day that DAY by itself would
represent.

   A comma following a day of the week item is ignored.


File: coreutils.info,  Node: Relative items in date strings,  Next: Pure numbers in date strings,  Prev: Day of week items,  Up: Date input formats

27.6 Relative items in date strings
===================================

"Relative items" adjust a date (or the current date if none) forward or
backward.  The effects of relative items accumulate.  Here are some
examples:

     1 year
     1 year ago
     3 years
     2 days

   The unit of time displacement may be selected by the string `year'
or `month' for moving by whole years or months.  These are fuzzy units,
as years and months are not all of equal duration.  More precise units
are `fortnight' which is worth 14 days, `week' worth 7 days, `day'
worth 24 hours, `hour' worth 60 minutes, `minute' or `min' worth 60
seconds, and `second' or `sec' worth one second.  An `s' suffix on
these units is accepted and ignored.

   The unit of time may be preceded by a multiplier, given as an
optionally signed number.  Unsigned numbers are taken as positively
signed.  No number at all implies 1 for a multiplier.  Following a
relative item by the string `ago' is equivalent to preceding the unit
by a multiplier with value -1.

   The string `tomorrow' is worth one day in the future (equivalent to
`day'), the string `yesterday' is worth one day in the past (equivalent
to `day ago').

   The strings `now' or `today' are relative items corresponding to
zero-valued time displacement, these strings come from the fact a
zero-valued time displacement represents the current time when not
otherwise changed by previous items.  They may be used to stress other
items, like in `12:00 today'.  The string `this' also has the meaning
of a zero-valued time displacement, but is preferred in date strings
like `this thursday'.

   When a relative item causes the resulting date to cross a boundary
where the clocks were adjusted, typically for daylight saving time, the
resulting date and time are adjusted accordingly.

   The fuzz in units can cause problems with relative items.  For
example, `2003-07-31 -1 month' might evaluate to 2003-07-01, because
2003-06-31 is an invalid date.  To determine the previous month more
reliably, you can ask for the month before the 15th of the current
month.  For example:

     $ date -R
     Thu, 31 Jul 2003 13:02:39 -0700
     $ date --date='-1 month' +'Last month was %B?'
     Last month was July?
     $ date --date="$(date +%Y-%m-15) -1 month" +'Last month was %B!'
     Last month was June!

   Also, take care when manipulating dates around clock changes such as
daylight saving leaps.  In a few cases these have added or subtracted
as much as 24 hours from the clock, so it is often wise to adopt
universal time by setting the `TZ' environment variable to `UTC0'
before embarking on calendrical calculations.


File: coreutils.info,  Node: Pure numbers in date strings,  Next: Seconds since the Epoch,  Prev: Relative items in date strings,  Up: Date input formats

27.7 Pure numbers in date strings
=================================

The precise interpretation of a pure decimal number depends on the
context in the date string.

   If the decimal number is of the form YYYYMMDD and no other calendar
date item (*note Calendar date items::) appears before it in the date
string, then YYYY is read as the year, MM as the month number and DD as
the day of the month, for the specified calendar date.

   If the decimal number is of the form HHMM and no other time of day
item appears before it in the date string, then HH is read as the hour
of the day and MM as the minute of the hour, for the specified time of
day.  MM can also be omitted.

   If both a calendar date and a time of day appear to the left of a
number in the date string, but no relative item, then the number
overrides the year.


File: coreutils.info,  Node: Seconds since the Epoch,  Next: Specifying time zone rules,  Prev: Pure numbers in date strings,  Up: Date input formats

27.8 Seconds since the Epoch
============================

If you precede a number with `@', it represents an internal time stamp
as a count of seconds.  The number can contain an internal decimal
point (either `.' or `,'); any excess precision not supported by the
internal representation is truncated toward minus infinity.  Such a
number cannot be combined with any other date item, as it specifies a
complete time stamp.

   Internally, computer times are represented as a count of seconds
since an epoch--a well-defined point of time.  On GNU and POSIX
systems, the epoch is 1970-01-01 00:00:00 UTC, so `@0' represents this
time, `@1' represents 1970-01-01 00:00:01 UTC, and so forth.  GNU and
most other POSIX-compliant systems support such times as an extension
to POSIX, using negative counts, so that `@-1' represents 1969-12-31
23:59:59 UTC.

   Traditional Unix systems count seconds with 32-bit two's-complement
integers and can represent times from 1901-12-13 20:45:52 through
2038-01-19 03:14:07 UTC.  More modern systems use 64-bit counts of
seconds with nanosecond subcounts, and can represent all the times in
the known lifetime of the universe to a resolution of 1 nanosecond.

   On most hosts, these counts ignore the presence of leap seconds.
For example, on most hosts `@915148799' represents 1998-12-31 23:59:59
UTC, `@915148800' represents 1999-01-01 00:00:00 UTC, and there is no
way to represent the intervening leap second 1998-12-31 23:59:60 UTC.


File: coreutils.info,  Node: Specifying time zone rules,  Next: Authors of get_date,  Prev: Seconds since the Epoch,  Up: Date input formats

27.9 Specifying time zone rules
===============================

Normally, dates are interpreted using the rules of the current time
zone, which in turn are specified by the `TZ' environment variable, or
by a system default if `TZ' is not set.  To specify a different set of
default time zone rules that apply just to one date, start the date
with a string of the form `TZ="RULE"'.  The two quote characters (`"')
must be present in the date, and any quotes or backslashes within RULE
must be escaped by a backslash.

   For example, with the GNU `date' command you can answer the question
"What time is it in New York when a Paris clock shows 6:30am on October
31, 2004?" by using a date beginning with `TZ="Europe/Paris"' as shown
in the following shell transcript:

     $ export TZ="America/New_York"
     $ date --date='TZ="Europe/Paris" 2004-10-31 06:30'
     Sun Oct 31 01:30:00 EDT 2004

   In this example, the `--date' operand begins with its own `TZ'
setting, so the rest of that operand is processed according to
`Europe/Paris' rules, treating the string `2004-10-31 06:30' as if it
were in Paris.  However, since the output of the `date' command is
processed according to the overall time zone rules, it uses New York
time.  (Paris was normally six hours ahead of New York in 2004, but
this example refers to a brief Halloween period when the gap was five
hours.)

   A `TZ' value is a rule that typically names a location in the `tz'
database (http://www.twinsun.com/tz/tz-link.htm).  A recent catalog of
location names appears in the TWiki Date and Time Gateway
(http://twiki.org/cgi-bin/xtra/tzdate).  A few non-GNU hosts require a
colon before a location name in a `TZ' setting, e.g.,
`TZ=":America/New_York"'.

   The `tz' database includes a wide variety of locations ranging from
`Arctic/Longyearbyen' to `Antarctica/South_Pole', but if you are at sea
and have your own private time zone, or if you are using a non-GNU host
that does not support the `tz' database, you may need to use a POSIX
rule instead.  Simple POSIX rules like `UTC0' specify a time zone
without daylight saving time; other rules can specify simple daylight
saving regimes.  *Note Specifying the Time Zone with `TZ': (libc)TZ
Variable.


File: coreutils.info,  Node: Authors of get_date,  Prev: Specifying time zone rules,  Up: Date input formats

27.10 Authors of `get_date'
===========================

`get_date' was originally implemented by Steven M. Bellovin
(<smb@research.att.com>) while at the University of North Carolina at
Chapel Hill.  The code was later tweaked by a couple of people on
Usenet, then completely overhauled by Rich $alz (<rsalz@bbn.com>) and
Jim Berets (<jberets@bbn.com>) in August, 1990.  Various revisions for
the GNU system were made by David MacKenzie, Jim Meyering, Paul Eggert
and others.

   This chapter was originally produced by Franc,ois Pinard
(<pinard@iro.umontreal.ca>) from the `getdate.y' source code, and then
edited by K. Berry (<kb@cs.umb.edu>).


File: coreutils.info,  Node: Opening the software toolbox,  Next: Copying This Manual,  Prev: Date input formats,  Up: Top

28 Opening the Software Toolbox
*******************************

An earlier version of this chapter appeared in 2 (June 1994).  It was
written by Arnold Robbins.

* Menu:

* Toolbox introduction::        Toolbox introduction
* I/O redirection::             I/O redirection
* The who command::             The `who' command
* The cut command::             The `cut' command
* The sort command::            The `sort' command
* The uniq command::            The `uniq' command
* Putting the tools together::  Putting the tools together


File: coreutils.info,  Node: Toolbox introduction,  Next: I/O redirection,  Up: Opening the software toolbox

Toolbox Introduction
====================

This month's column is only peripherally related to the GNU Project, in
that it describes a number of the GNU tools on your GNU/Linux system
and how they might be used.  What it's really about is the "Software
Tools" philosophy of program development and usage.

   The software tools philosophy was an important and integral concept
in the initial design and development of Unix (of which Linux and GNU
are essentially clones).  Unfortunately, in the modern day press of
Internetworking and flashy GUIs, it seems to have fallen by the
wayside.  This is a shame, since it provides a powerful mental model
for solving many kinds of problems.

   Many people carry a Swiss Army knife around in their pants pockets
(or purse).  A Swiss Army knife is a handy tool to have: it has several
knife blades, a screwdriver, tweezers, toothpick, nail file, corkscrew,
and perhaps a number of other things on it.  For the everyday, small
miscellaneous jobs where you need a simple, general purpose tool, it's
just the thing.

   On the other hand, an experienced carpenter doesn't build a house
using a Swiss Army knife.  Instead, he has a toolbox chock full of
specialized tools--a saw, a hammer, a screwdriver, a plane, and so on.
And he knows exactly when and where to use each tool; you won't catch
him hammering nails with the handle of his screwdriver.

   The Unix developers at Bell Labs were all professional programmers
and trained computer scientists.  They had found that while a
one-size-fits-all program might appeal to a user because there's only
one program to use, in practice such programs are

  a. difficult to write,

  b. difficult to maintain and debug, and

  c. difficult to extend to meet new situations.

   Instead, they felt that programs should be specialized tools.  In
short, each program "should do one thing well."  No more and no less.
Such programs are simpler to design, write, and get right--they only do
one thing.

   Furthermore, they found that with the right machinery for hooking
programs together, that the whole was greater than the sum of the
parts.  By combining several special purpose programs, you could
accomplish a specific task that none of the programs was designed for,
and accomplish it much more quickly and easily than if you had to write
a special purpose program.  We will see some (classic) examples of this
further on in the column.  (An important additional point was that, if
necessary, take a detour and build any software tools you may need
first, if you don't already have something appropriate in the toolbox.)


File: coreutils.info,  Node: I/O redirection,  Next: The who command,  Prev: Toolbox introduction,  Up: Opening the software toolbox

I/O Redirection
===============

Hopefully, you are familiar with the basics of I/O redirection in the
shell, in particular the concepts of "standard input," "standard
output," and "standard error".  Briefly, "standard input" is a data
source, where data comes from.  A program should not need to either
know or care if the data source is a disk file, a keyboard, a magnetic
tape, or even a punched card reader.  Similarly, "standard output" is a
data sink, where data goes to.  The program should neither know nor
care where this might be.  Programs that only read their standard
input, do something to the data, and then send it on, are called
"filters", by analogy to filters in a water pipeline.

   With the Unix shell, it's very easy to set up data pipelines:

     program_to_create_data | filter1 | ... | filterN > final.pretty.data

   We start out by creating the raw data; each filter applies some
successive transformation to the data, until by the time it comes out
of the pipeline, it is in the desired form.

   This is fine and good for standard input and standard output.  Where
does the standard error come in to play?  Well, think about `filter1' in
the pipeline above.  What happens if it encounters an error in the data
it sees?  If it writes an error message to standard output, it will just
disappear down the pipeline into `filter2''s input, and the user will
probably never see it.  So programs need a place where they can send
error messages so that the user will notice them.  This is standard
error, and it is usually connected to your console or window, even if
you have redirected standard output of your program away from your
screen.

   For filter programs to work together, the format of the data has to
be agreed upon.  The most straightforward and easiest format to use is
simply lines of text.  Unix data files are generally just streams of
bytes, with lines delimited by the ASCII LF (Line Feed) character,
conventionally called a "newline" in the Unix literature.  (This is
`'\n'' if you're a C programmer.)  This is the format used by all the
traditional filtering programs.  (Many earlier operating systems had
elaborate facilities and special purpose programs for managing binary
data.  Unix has always shied away from such things, under the
philosophy that it's easiest to simply be able to view and edit your
data with a text editor.)

   OK, enough introduction.  Let's take a look at some of the tools,
and then we'll see how to hook them together in interesting ways.   In
the following discussion, we will only present those command line
options that interest us.  As you should always do, double check your
system documentation for the full story.


File: coreutils.info,  Node: The who command,  Next: The cut command,  Prev: I/O redirection,  Up: Opening the software toolbox

The `who' Command
=================

The first program is the `who' command.  By itself, it generates a list
of the users who are currently logged in.  Although I'm writing this on
a single-user system, we'll pretend that several people are logged in:

     $ who
     -| arnold   console Jan 22 19:57
     -| miriam   ttyp0   Jan 23 14:19(:0.0)
     -| bill     ttyp1   Jan 21 09:32(:0.0)
     -| arnold   ttyp2   Jan 23 20:48(:0.0)

   Here, the `$' is the usual shell prompt, at which I typed `who'.
There are three people logged in, and I am logged in twice.  On
traditional Unix systems, user names are never more than eight
characters long.  This little bit of trivia will be useful later.  The
output of `who' is nice, but the data is not all that exciting.


File: coreutils.info,  Node: The cut command,  Next: The sort command,  Prev: The who command,  Up: Opening the software toolbox

The `cut' Command
=================

The next program we'll look at is the `cut' command.  This program cuts
out columns or fields of input data.  For example, we can tell it to
print just the login name and full name from the `/etc/passwd' file.
The `/etc/passwd' file has seven fields, separated by colons:

     arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash

   To get the first and fifth fields, we would use `cut' like this:

     $ cut -d: -f1,5 /etc/passwd
     -| root:Operator
     ...
     -| arnold:Arnold D. Robbins
     -| miriam:Miriam A. Robbins
     ...

   With the `-c' option, `cut' will cut out specific characters (i.e.,
columns) in the input lines.  This is useful for input data that has
fixed width fields, and does not have a field separator.  For example,
list the Monday dates for the current month:

     $ cal | cut -c 3-5
     -|Mo
     -|
     -|  6
     -| 13
     -| 20
     -| 27


File: coreutils.info,  Node: The sort command,  Next: The uniq command,  Prev: The cut command,  Up: Opening the software toolbox

The `sort' Command
==================

Next we'll look at the `sort' command.  This is one of the most
powerful commands on a Unix-style system; one that you will often find
yourself using when setting up fancy data plumbing.

   The `sort' command reads and sorts each file named on the command
line.  It then merges the sorted data and writes it to standard output.
It will read standard input if no files are given on the command line
(thus making it into a filter).  The sort is based on the character
collating sequence or based on user-supplied ordering criteria.


File: coreutils.info,  Node: The uniq command,  Next: Putting the tools together,  Prev: The sort command,  Up: Opening the software toolbox

The `uniq' Command
==================

Finally (at least for now), we'll look at the `uniq' program.  When
sorting data, you will often end up with duplicate lines, lines that
are identical.  Usually, all you need is one instance of each line.
This is where `uniq' comes in.  The `uniq' program reads its standard
input.  It prints only one copy of each repeated line.  It does have
several options.  Later on, we'll use the `-c' option, which prints
each unique line, preceded by a count of the number of times that line
occurred in the input.


File: coreutils.info,  Node: Putting the tools together,  Prev: The uniq command,  Up: Opening the software toolbox

Putting the Tools Together
==========================

Now, let's suppose this is a large ISP server system with dozens of
users logged in.  The management wants the system administrator to
write a program that will generate a sorted list of logged in users.
Furthermore, even if a user is logged in multiple times, his or her
name should only show up in the output once.

   The administrator could sit down with the system documentation and
write a C program that did this.  It would take perhaps a couple of
hundred lines of code and about two hours to write it, test it, and
debug it.  However, knowing the software toolbox, the administrator can
instead start out by generating just a list of logged on users:

     $ who | cut -c1-8
     -| arnold
     -| miriam
     -| bill
     -| arnold

   Next, sort the list:

     $ who | cut -c1-8 | sort
     -| arnold
     -| arnold
     -| bill
     -| miriam

   Finally, run the sorted list through `uniq', to weed out duplicates:

     $ who | cut -c1-8 | sort | uniq
     -| arnold
     -| bill
     -| miriam

   The `sort' command actually has a `-u' option that does what `uniq'
does.  However, `uniq' has other uses for which one cannot substitute
`sort -u'.

   The administrator puts this pipeline into a shell script, and makes
it available for all the users on the system (`#' is the system
administrator, or `root', prompt):

     # cat > /usr/local/bin/listusers
     who | cut -c1-8 | sort | uniq
     ^D
     # chmod +x /usr/local/bin/listusers

   There are four major points to note here.  First, with just four
programs, on one command line, the administrator was able to save about
two hours worth of work.  Furthermore, the shell pipeline is just about
as efficient as the C program would be, and it is much more efficient in
terms of programmer time.  People time is much more expensive than
computer time, and in our modern "there's never enough time to do
everything" society, saving two hours of programmer time is no mean
feat.

   Second, it is also important to emphasize that with the
_combination_ of the tools, it is possible to do a special purpose job
never imagined by the authors of the individual programs.

   Third, it is also valuable to build up your pipeline in stages, as
we did here.  This allows you to view the data at each stage in the
pipeline, which helps you acquire the confidence that you are indeed
using these tools correctly.

   Finally, by bundling the pipeline in a shell script, other users can
use your command, without having to remember the fancy plumbing you set
up for them.  In terms of how you run them, shell scripts and compiled
programs are indistinguishable.

   After the previous warm-up exercise, we'll look at two additional,
more complicated pipelines.  For them, we need to introduce two more
tools.

   The first is the `tr' command, which stands for "transliterate."
The `tr' command works on a character-by-character basis, changing
characters.  Normally it is used for things like mapping upper case to
lower case:

     $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
     -| this example has mixed case!

   There are several options of interest:

`-c'
     work on the complement of the listed characters, i.e., operations
     apply to characters not in the given set

`-d'
     delete characters in the first set from the output

`-s'
     squeeze repeated characters in the output into just one character.

   We will be using all three options in a moment.

   The other command we'll look at is `comm'.  The `comm' command takes
two sorted input files as input data, and prints out the files' lines
in three columns.  The output columns are the data lines unique to the
first file, the data lines unique to the second file, and the data
lines that are common to both.  The `-1', `-2', and `-3' command line
options _omit_ the respective columns.  (This is non-intuitive and
takes a little getting used to.)  For example:

     $ cat f1
     -| 11111
     -| 22222
     -| 33333
     -| 44444
     $ cat f2
     -| 00000
     -| 22222
     -| 33333
     -| 55555
     $ comm f1 f2
     -|         00000
     -| 11111
     -|                 22222
     -|                 33333
     -| 44444
     -|         55555

   The file name `-' tells `comm' to read standard input instead of a
regular file.

   Now we're ready to build a fancy pipeline.  The first application is
a word frequency counter.  This helps an author determine if he or she
is over-using certain words.

   The first step is to change the case of all the letters in our input
file to one case.  "The" and "the" are the same word when doing
counting.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...

   The next step is to get rid of punctuation.  Quoted words and
unquoted words should be treated identically; it's easiest to just get
the punctuation out of the way.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...

   The second `tr' command operates on the complement of the listed
characters, which are all the letters, the digits, the underscore, and
the blank.  The `\n' represents the newline character; it has to be
left alone.  (The ASCII tab character should also be included for good
measure in a production script.)

   At this point, we have data consisting of words separated by blank
space.  The words only contain alphanumeric characters (and the
underscore).  The next step is break the data apart so that we have one
word per line.  This makes the counting operation much easier, as we
will see shortly.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | ...

   This command turns blanks into newlines.  The `-s' option squeezes
multiple newline characters in the output into just one.  This helps us
avoid blank lines.  (The `>' is the shell's "secondary prompt."  This
is what the shell prints when it notices you haven't finished typing in
all of a command.)

   We now have data consisting of one word per line, no punctuation,
all one case.  We're ready to count each word:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort | uniq -c | ...

   At this point, the data might look something like this:

          60 a
           2 able
           6 about
           1 above
           2 accomplish
           1 acquire
           1 actually
           2 additional

   The output is sorted by word, not by count!  What we want is the most
frequently used words first.  Fortunately, this is easy to accomplish,
with the help of two more `sort' options:

`-n'
     do a numeric sort, not a textual one

`-r'
     reverse the order of the sort

   The final pipeline looks like this:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
     -|    156 the
     -|     60 a
     -|     58 to
     -|     51 of
     -|     51 and
     ...

   Whew!  That's a lot to digest.  Yet, the same principles apply.
With six commands, on two lines (really one long one split for
convenience), we've created a program that does something interesting
and useful, in much less time than we could have written a C program to
do the same thing.

   A minor modification to the above pipeline can give us a simple
spelling checker!  To determine if you've spelled a word correctly, all
you have to do is look it up in a dictionary.  If it is not there, then
chances are that your spelling is incorrect.  So, we need a dictionary.
The conventional location for a dictionary is `/usr/dict/words'.  On my
GNU/Linux system,(1) this is a is a sorted, 45,402 word dictionary.

   Now, how to compare our file with the dictionary?  As before, we
generate a sorted list of words, one per line:

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort -u | ...

   Now, all we need is a list of words that are _not_ in the
dictionary.  Here is where the `comm' command comes in.

     $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
     > tr -s ' ' '\n' | sort -u |
     > comm -23 - /usr/dict/words

   The `-2' and `-3' options eliminate lines that are only in the
dictionary (the second file), and lines that are in both files.  Lines
only in the first file (standard input, our stream of words), are words
that are not in the dictionary.  These are likely candidates for
spelling errors.  This pipeline was the first cut at a production
spelling checker on Unix.

   There are some other tools that deserve brief mention.

`grep'
     search files for text that matches a regular expression

`wc'
     count lines, words, characters

`tee'
     a T-fitting for data pipes, copies data to files and to standard
     output

`sed'
     the stream editor, an advanced tool

`awk'
     a data manipulation language, another advanced tool

   The software tools philosophy also espoused the following bit of
advice: "Let someone else do the hard part."  This means, take
something that gives you most of what you need, and then massage it the
rest of the way until it's in the form that you want.

   To summarize:

  1. Each program should do one thing well.  No more, no less.

  2. Combining programs with appropriate plumbing leads to results where
     the whole is greater than the sum of the parts.  It also leads to
     novel uses of programs that the authors might never have imagined.

  3. Programs should never print extraneous header or trailer data,
     since these could get sent on down a pipeline.  (A point we didn't
     mention earlier.)

  4. Let someone else do the hard part.

  5. Know your toolbox!  Use each program appropriately.  If you don't
     have an appropriate tool, build one.

   As of this writing, all the programs we've discussed are available
via anonymous `ftp' from:
`ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz'.  (There may be
more recent versions available now.)

   None of what I have presented in this column is new.  The Software
Tools philosophy was first introduced in the book `Software Tools', by
Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
This book showed how to write and use software tools.  It was written in
1976, using a preprocessor for FORTRAN named `ratfor' (RATional
FORtran).  At the time, C was not as ubiquitous as it is now; FORTRAN
was.  The last chapter presented a `ratfor' to FORTRAN processor,
written in `ratfor'.  `ratfor' looks an awful lot like C; if you know
C, you won't have any problem following the code.

   In 1981, the book was updated and made available as `Software Tools
in Pascal' (Addison-Wesley, ISBN 0-201-10342-7).  Both books are still
in print and are well worth reading if you're a programmer.  They
certainly made a major change in how I view programming.

   The programs in both books are available from Brian Kernighan's home
page (http://cm.bell-labs.com/who/bwk).  For a number of years, there
was an active Software Tools Users Group, whose members had ported the
original `ratfor' programs to essentially every computer system with a
FORTRAN compiler.  The popularity of the group waned in the middle 1980s
as Unix began to spread beyond universities.

   With the current proliferation of GNU code and other clones of Unix
programs, these programs now receive little attention; modern C
versions are much more efficient and do more than these programs do.
Nevertheless, as exposition of good programming style, and evangelism
for a still-valuable philosophy, these books are unparalleled, and I
recommend them highly.

   Acknowledgment: I would like to express my gratitude to Brian
Kernighan of Bell Labs, the original Software Toolsmith, for reviewing
this column.

   ---------- Footnotes ----------

   (1) Redhat Linux 6.1, for the November 2000 revision of this article.


File: coreutils.info,  Node: Copying This Manual,  Next: Index,  Prev: Opening the software toolbox,  Up: Top

Appendix A Copying This Manual
******************************

* Menu:

* GNU Free Documentation License::  License for copying this manual.


File: coreutils.info,  Node: GNU Free Documentation License,  Up: Copying This Manual

A.1 GNU Free Documentation License
==================================

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
     51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

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     This License is a kind of "copyleft", which means that derivative
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     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
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          previous versions it was based on.  These may be placed in
          the "History" section.  You may omit a network location for a
          work that was published at least four years before the
          Document itself, or if the original publisher of the version
          it refers to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the
          section all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document,
          unaltered in their text and in their titles.  Section numbers
          or the equivalent are not considered part of the section
          titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option
     designate some or all of these sections as invariant.  To do this,
     add their titles to the list of Invariant Sections in the Modified
     Version's license notice.  These titles must be distinct from any
     other section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties--for example, statements of peer review or that the text
     has been approved by an organization as the authoritative
     definition of a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end
     of the list of Cover Texts in the Modified Version.  Only one
     passage of Front-Cover Text and one of Back-Cover Text may be
     added by (or through arrangements made by) any one entity.  If the
     Document already includes a cover text for the same cover,
     previously added by you or by arrangement made by the same entity
     you are acting on behalf of, you may not add another; but you may
     replace the old one, on explicit permission from the previous
     publisher that added the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination
     all of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the
     documents in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow
     this License in all other respects regarding verbatim copying of
     that document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of
     a storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     `http://www.gnu.org/copyleft/'.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If
     the Document does not specify a version number of this License,
     you may choose any version ever published (not as a draft) by the
     Free Software Foundation.

ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


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