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diff --git a/gzip.doc b/gzip.doc new file mode 100644 index 0000000..e8efea7 --- /dev/null +++ b/gzip.doc @@ -0,0 +1,388 @@ +GZIP(1) General Commands Manual GZIP(1) + +1mNAME0m + gzip, gunzip, zcat - compress or expand files + +1mSYNOPSIS0m + 1mgzip 22m[ 1m-acdfhklLnNrtvV19 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ] + 1mgunzip 22m[ 1m-acfhklLnNrtvV 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ] + 1mzcat 22m[ 1m-fhLV 22m] [ 4mname24m 4m...24m ] + +1mDESCRIPTION0m + 4mGzip24m reduces the size of the named files using Lempel-Ziv coding + (LZ77). Whenever possible, each file is replaced by one with the + extension 1m.gz22m, while keeping the same ownership modes, access and modi- + fication times. (The default extension is 1m-gz 22mfor VMS, 1mz 22mfor MSDOS, + OS/2 FAT, Windows NT FAT and Atari.) If no files are specified, or if + a file name is "-", the standard input is compressed to the standard + output. 4mGzip24m will only attempt to compress regular files. In particu- + lar, it will ignore symbolic links. + + If the compressed file name is too long for its file system, 4mgzip24m trun- + cates it. 4mGzip24m attempts to truncate only the parts of the file name + longer than 3 characters. (A part is delimited by dots.) If the name + consists of small parts only, the longest parts are truncated. For + example, if file names are limited to 14 characters, gzip.msdos.exe is + compressed to gzi.msd.exe.gz. Names are not truncated on systems which + do not have a limit on file name length. + + By default, 4mgzip24m keeps the original file name and timestamp in the com- + pressed file. These are used when decompressing the file with the 1m-N0m + option. This is useful when the compressed file name was truncated or + when the time stamp was not preserved after a file transfer. + + Compressed files can be restored to their original form using 4mgzip24m 4m-d0m + or 4mgunzip24m or 4mzcat24m. If the original name saved in the compressed file + is not suitable for its file system, a new name is constructed from the + original one to make it legal. + + 4mgunzip24m takes a list of files on its command line and replaces each file + whose name ends with .gz, -gz, .z, -z, or _z (ignoring case) and which + begins with the correct magic number with an uncompressed file without + the original extension. 4mgunzip24m also recognizes the special extensions + 1m.tgz 22mand 1m.taz 22mas shorthands for 1m.tar.gz 22mand 1m.tar.Z 22mrespectively. When + compressing, 4mgzip24m uses the 1m.tgz 22mextension if necessary instead of trun- + cating a file with a 1m.tar 22mextension. + + 4mgunzip24m can currently decompress files created by 4mgzip24m, 4mzip24m, 4mcompress24m, + 4mcompress24m 4m-H24m or 4mpack24m. The detection of the input format is automatic. + When using the first two formats, 4mgunzip24m checks a 32 bit CRC. For 4mpack0m + and 4mgunzip24m checks the uncompressed length. The standard 4mcompress24m format + was not designed to allow consistency checks. However 4mgunzip24m is some- + times able to detect a bad .Z file. If you get an error when uncom- + pressing a .Z file, do not assume that the .Z file is correct simply + because the standard 4muncompress24m does not complain. This generally means + that the standard 4muncompress24m does not check its input, and happily gen- + erates garbage output. The SCO compress -H format (lzh compression + method) does not include a CRC but also allows some consistency checks. + + Files created by 4mzip24m can be uncompressed by gzip only if they have a + single member compressed with the 'deflation' method. This feature is + only intended to help conversion of tar.zip files to the tar.gz format. + To extract a 4mzip24m file with a single member, use a command like 4mgunzip0m + 4m<foo.zip24m or 4mgunzip24m 4m-S24m 4m.zip24m 4mfoo.zip24m. To extract zip files with several + members, use 4munzip24m instead of 4mgunzip24m. + + 4mzcat24m is identical to 4mgunzip24m 1m-c22m. (On some systems, 4mzcat24m may be + installed as 4mgzcat24m to preserve the original link to 4mcompress24m.) 4mzcat0m + uncompresses either a list of files on the command line or its standard + input and writes the uncompressed data on standard output. 4mzcat24m will + uncompress files that have the correct magic number whether they have a + 1m.gz 22msuffix or not. + + 4mGzip24m uses the Lempel-Ziv algorithm used in 4mzip24m and PKZIP. The amount + of compression obtained depends on the size of the input and the dis- + tribution of common substrings. Typically, text such as source code or + English is reduced by 60-70%. Compression is generally much better + than that achieved by LZW (as used in 4mcompress24m), Huffman coding (as + used in 4mpack24m), or adaptive Huffman coding (4mcompact24m). + + Compression is always performed, even if the compressed file is + slightly larger than the original. The worst case expansion is a few + bytes for the gzip file header, plus 5 bytes every 32K block, or an + expansion ratio of 0.015% for large files. Note that the actual number + of used disk blocks almost never increases. 4mgzip24m preserves the mode, + ownership and timestamps of files when compressing or decompressing. + +1mOPTIONS0m + 1m-a --ascii0m + Ascii text mode: convert end-of-lines using local conventions. + This option is supported only on some non-Unix systems. For + MSDOS, CR LF is converted to LF when compressing, and LF is con- + verted to CR LF when decompressing. + + 1m-c --stdout --to-stdout0m + Write output on standard output; keep original files unchanged. + If there are several input files, the output consists of a + sequence of independently compressed members. To obtain better + compression, concatenate all input files before compressing + them. + + 1m-d --decompress --uncompress0m + Decompress. + + 1m-f --force0m + Force compression or decompression even if the file has multiple + links or the corresponding file already exists, or if the com- + pressed data is read from or written to a terminal. If the input + data is not in a format recognized by 4mgzip24m, and if the option + --stdout is also given, copy the input data without change to + the standard output: let 4mzcat24m behave as 4mcat24m. If 1m-f 22mis not + given, and when not running in the background, 4mgzip24m prompts to + verify whether an existing file should be overwritten. + + 1m-h --help0m + Display a help screen and quit. + + 1m-k --keep0m + Keep (don't delete) input files during compression or decompres- + sion. + + 1m-l --list0m + For each compressed file, list the following fields: + + compressed size: size of the compressed file + uncompressed size: size of the uncompressed file + ratio: compression ratio (0.0% if unknown) + uncompressed_name: name of the uncompressed file + + The uncompressed size is given as -1 for files not in gzip for- + mat, such as compressed .Z files. To get the uncompressed size + for such a file, you can use: + + zcat file.Z | wc -c + + In combination with the --verbose option, the following fields + are also displayed: + + method: compression method + crc: the 32-bit CRC of the uncompressed data + date & time: time stamp for the uncompressed file + + The compression methods currently supported are deflate, com- + press, lzh (SCO compress -H) and pack. The crc is given as + ffffffff for a file not in gzip format. + + With --name, the uncompressed name, date and time are those + stored within the compress file if present. + + With --verbose, the size totals and compression ratio for all + files is also displayed, unless some sizes are unknown. With + --quiet, the title and totals lines are not displayed. + + 1m-L --license0m + Display the 4mgzip24m license and quit. + + 1m-n --no-name0m + When compressing, do not save the original file name and time + stamp by default. (The original name is always saved if the name + had to be truncated.) When decompressing, do not restore the + original file name if present (remove only the 4mgzip24m suffix from + the compressed file name) and do not restore the original time + stamp if present (copy it from the compressed file). This option + is the default when decompressing. + + 1m-N --name0m + When compressing, always save the original file name and time + stamp; this is the default. When decompressing, restore the + original file name and time stamp if present. This option is + useful on systems which have a limit on file name length or when + the time stamp has been lost after a file transfer. + + 1m-q --quiet0m + Suppress all warnings. + + 1m-r --recursive0m + Travel the directory structure recursively. If any of the file + names specified on the command line are directories, 4mgzip24m will + descend into the directory and compress all the files it finds + there (or decompress them in the case of 4mgunzip24m ). + + 1m-S .suf --suffix .suf0m + When compressing, use suffix .suf instead of .gz. Any non-empty + suffix can be given, but suffixes other than .z and .gz should + be avoided to avoid confusion when files are transferred to + other systems. + + When decompressing, add .suf to the beginning of the list of + suffixes to try, when deriving an output file name from an input + file name. + + 1m--synchronous0m + Use synchronous output. With this option, 4mgzip24m is less likely + to lose data during a system crash, but it can be considerably + slower. + + 1m-t --test0m + Test. Check the compressed file integrity. + + 1m-v --verbose0m + Verbose. Display the name and percentage reduction for each file + compressed or decompressed. + + 1m-V --version0m + Version. Display the version number and compilation options then + quit. + + 1m-# --fast --best0m + Regulate the speed of compression using the specified digit 4m#24m, + where 1m-1 22mor 1m--fast 22mindicates the fastest compression method + (less compression) and 1m-9 22mor 1m--best 22mindicates the slowest com- + pression method (best compression). The default compression + level is 1m-6 22m(that is, biased towards high compression at expense + of speed). + + 1m--rsyncable0m + When you synchronize a compressed file between two computers, + this option allows rsync to transfer only files that were + changed in the archive instead of the entire archive. Normally, + after a change is made to any file in the archive, the compres- + sion algorithm can generate a new version of the archive that + does not match the previous version of the archive. In this + case, rsync transfers the entire new version of the archive to + the remote computer. With this option, rsync can transfer only + the changed files as well as a small amount of metadata that is + required to update the archive structure in the area that was + changed. + +1mADVANCED USAGE0m + Multiple compressed files can be concatenated. In this case, 4mgunzip0m + will extract all members at once. For example: + + gzip -c file1 > foo.gz + gzip -c file2 >> foo.gz + + Then + + gunzip -c foo + + is equivalent to + + cat file1 file2 + + In case of damage to one member of a .gz file, other members can still + be recovered (if the damaged member is removed). However, you can get + better compression by compressing all members at once: + + cat file1 file2 | gzip > foo.gz + + compresses better than + + gzip -c file1 file2 > foo.gz + + If you want to recompress concatenated files to get better compression, + do: + + gzip -cd old.gz | gzip > new.gz + + If a compressed file consists of several members, the uncompressed size + and CRC reported by the --list option applies to the last member only. + If you need the uncompressed size for all members, you can use: + + gzip -cd file.gz | wc -c + + If you wish to create a single archive file with multiple members so + that members can later be extracted independently, use an archiver such + as tar or zip. GNU tar supports the -z option to invoke gzip transpar- + ently. gzip is designed as a complement to tar, not as a replacement. + +1mENVIRONMENT0m + The obsolescent environment variable 1mGZIP 22mcan hold a set of default + options for 4mgzip24m. These options are interpreted first and can be over- + written by explicit command line parameters. As this can cause prob- + lems when using scripts, this feature is supported only for options + that are reasonably likely to not cause too much harm, and 4mgzip24m warns + if it is used. This feature will be removed in a future release of + 4mgzip24m. + + You can use an alias or script instead. For example, if 4mgzip24m is in the + directory 1m/usr/bin 22myou can prepend 1m$HOME/bin 22mto your 1mPATH 22mand create an + executable script 1m$HOME/bin/gzip 22mcontaining the following: + + #! /bin/sh + export PATH=/usr/bin + exec gzip -9 "$@" + + On VMS, the name of the obsolescent environment variable is GZIP_OPT, + to avoid a conflict with the symbol set for invocation of the program. + +1mSEE ALSO0m + znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), com- + press(1) + + The 4mgzip24m file format is specified in P. Deutsch, GZIP file format spec- + ification version 4.3, 1m<http://www.ietf.org/rfc/rfc1952.txt>22m, Internet + RFC 1952 (May 1996). The 4mzip24m deflation format is specified in P. + Deutsch, DEFLATE Compressed Data Format Specification version 1.3, + 1m<http://www.ietf.org/rfc/rfc1951.txt>22m, Internet RFC 1951 (May 1996). + +1mDIAGNOSTICS0m + Exit status is normally 0; if an error occurs, exit status is 1. If a + warning occurs, exit status is 2. + + Usage: gzip [-cdfhklLnNrtvV19] [-S suffix] [file ...] + Invalid options were specified on the command line. + + 4mfile24m: not in gzip format + The file specified to 4mgunzip24m has not been compressed. + + 4mfile24m: Corrupt input. Use zcat to recover some data. + The compressed file has been damaged. The data up to the point + of failure can be recovered using + + zcat 4mfile24m > recover + + 4mfile24m: compressed with 4mxx24m bits, can only handle 4myy24m bits + 4mFile24m was compressed (using LZW) by a program that could deal + with more 4mbits24m than the decompress code on this machine. Recom- + press the file with gzip, which compresses better and uses less + memory. + + 4mfile24m: already has .gz suffix -- unchanged + The file is assumed to be already compressed. Rename the file + and try again. + + 4mfile24m already exists; do you wish to overwrite (y or n)? + Respond "y" if you want the output file to be replaced; "n" if + not. + + gunzip: corrupt input + A SIGSEGV violation was detected which usually means that the + input file has been corrupted. + + 4mxx.x%24m Percentage of the input saved by compression. + (Relevant only for 1m-v 22mand 1m-l22m.) + + -- not a regular file or directory: ignored + When the input file is not a regular file or directory, (e.g. a + symbolic link, socket, FIFO, device file), it is left unaltered. + + -- has 4mxx24m other links: unchanged + The input file has links; it is left unchanged. See 4mln24m(1) for + more information. Use the 1m-f 22mflag to force compression of multi- + ply-linked files. + +1mCAVEATS0m + When writing compressed data to a tape, it is generally necessary to + pad the output with zeroes up to a block boundary. When the data is + read and the whole block is passed to 4mgunzip24m for decompression, 4mgunzip0m + detects that there is extra trailing garbage after the compressed data + and emits a warning by default. You can use the --quiet option to sup- + press the warning. + +1mBUGS0m + The gzip format represents the input size modulo 2^32, so the --list + option reports incorrect uncompressed sizes and compression ratios for + uncompressed files 4 GB and larger. To work around this problem, you + can use the following command to discover a large uncompressed file's + true size: + + zcat file.gz | wc -c + + The --list option reports sizes as -1 and crc as ffffffff if the com- + pressed file is on a non seekable media. + + In some rare cases, the --best option gives worse compression than the + default compression level (-6). On some highly redundant files, 4mcom-0m + 4mpress24m compresses better than 4mgzip24m. + +1mCOPYRIGHT NOTICE0m + Copyright (C) 1998-1999, 2001-2002, 2012, 2015-2016 Free Software Foun- + dation, Inc. + Copyright (C) 1992, 1993 Jean-loup Gailly + + Permission is granted to make and distribute verbatim copies of this + manual provided the copyright notice and this permission notice are + preserved on all copies. + + Permission is granted to copy and distribute modified versions of this + manual under the conditions for verbatim copying, provided that the + entire resulting derived work is distributed under the terms of a per- + mission notice identical to this one. + + Permission is granted to copy and distribute translations of this man- + ual into another language, under the above conditions for modified ver- + sions, except that this permission notice may be stated in a transla- + tion approved by the Foundation. + + local GZIP(1) |