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.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, 1m22m, Internet RFC 1952 (May 1996). The 4mzip24m deflation format is specified in P. Deutsch, DEFLATE Compressed Data Format Specification version 1.3, 1m22m, 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)