GZIP(1)                                               General Commands Manual                                               GZIP(1)

NAME
       gzip, gunzip, zcat - compress or expand files

SYNOPSIS
       gzip [ -acdfhklLnNrtvV19 ] [-S suffix] [ name ...  ]
       gunzip [ -acfhklLnNrtvV ] [-S suffix] [ name ...  ]
       zcat [ -fhLV ] [ name ...  ]

DESCRIPTION
       Gzip  reduces  the  size of the named files using Lempel-Ziv coding (LZ77).  Whenever possible, each file is replaced by one
       with the extension .gz, while keeping the same ownership modes, access and modification times.  (The default extension is  z
       for  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.  Gzip will only attempt to compress regular files.  In particular, it  will  ignore  sym‐
       bolic links.

       If the compressed file name is too long for its file system, gzip truncates it.  Gzip 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  long‐
       est  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, gzip keeps the original file name and timestamp in the compressed file. These are used  when  decompressing  the
       file  with the -N option. This is useful when the compressed file name was truncated or when the timestamp was not preserved
       after a file transfer.

       Compressed files can be restored to their original form using gzip -d or gunzip or zcat.  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.

       gunzip takes a list of files on its command line and replaces each file whose name ends with .gz, -gz, .z, -z, or _z (ignor‐
       ing case) and which begins with the correct magic number with an uncompressed file without the original  extension.   gunzip
       also  recognizes  the special extensions .tgz and .taz as shorthands for .tar.gz and .tar.Z respectively.  When compressing,
       gzip uses the .tgz extension if necessary instead of truncating a file with a .tar extension.

       gunzip can currently decompress files created by gzip, zip, compress, compress -H or pack.  The detection of the input  for‐
       mat is automatic.  When using the first two formats, gunzip checks a 32 bit CRC. For pack and gunzip checks the uncompressed
       length. The standard compress format was not designed to allow consistency checks. However gunzip is sometimes able  to  de‐
       tect  a  bad .Z file. If you get an error when uncompressing a .Z file, do not assume that the .Z file is correct simply be‐
       cause the standard uncompress does not complain. This generally means that the standard uncompress does not check its input,
       and  happily  generates garbage output.  The SCO compress -H format (lzh compression method) does not include a CRC but also
       allows some consistency checks.

       Files created by zip 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 zip file with a single
       member, use a command like gunzip <foo.zip or gunzip -S .zip foo.zip.  To extract zip files with several members, use  unzip
       instead of gunzip.

       zcat  is  identical  to  gunzip  -c.  (On some systems, zcat may be installed as gzcat to preserve the original link to com‐
       press.)  zcat uncompresses either a list of files on the command line or its standard input and writes the uncompressed data
       on standard output.  zcat will uncompress files that have the correct magic number whether they have a .gz suffix or not.

       Gzip uses the Lempel-Ziv algorithm used in zip and PKZIP.  The amount of compression obtained depends on the size of the in‐
       put and the distribution of common substrings.  Typically, text such as source code or English is reduced by  60-70%.   Com‐
       pression  is  generally  much  better  than that achieved by LZW (as used in compress), Huffman coding (as used in pack), or
       adaptive Huffman coding (compact).

       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.  gzip preserves the mode,  ownership  and  timestamps  of
       files when compressing or decompressing.

OPTIONS
       -a --ascii
              Ascii  text  mode:  convert end-of-lines using local conventions. This option is supported only on some non-Unix sys‐
              tems. For MSDOS, CR LF is converted to LF when compressing, and LF is converted to CR LF when decompressing.

       -c --stdout --to-stdout
              Write output on standard output; keep original files unchanged.  If there are several input files,  the  output  con‐
              sists  of  a  sequence of independently compressed members. To obtain better compression, concatenate all input files
              before compressing them.

       -d --decompress --uncompress
              Decompress.

       -f --force
              Force compression or decompression even if the file has multiple links or the corresponding file already  exists,  or
              if  the  compressed  data  is  read from or written to a terminal. If the input data is not in a format recognized by
              gzip, and if the option --stdout is also given, copy the input data without change to the standard output:  let  zcat
              behave  as cat.  If -f is not given, and when not running in the background, gzip prompts to verify whether an exist‐
              ing file should be overwritten.

       -h --help
              Display a help screen and quit.

       -k --keep
              Keep (don't delete) input files during compression or decompression.

       -l --list
              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 format, such as compressed .Z files.  To  get  the  uncom‐
              pressed 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: timestamp for the uncompressed file

              The  compression methods currently supported are deflate, compress, 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.

       -L --license
              Display the gzip license and quit.

       -n --no-name
              When  compressing, do not save the original file name and timestamp 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
              gzip  suffix  from  the  compressed file name) and do not restore the original timestamp if present (copy it from the
              compressed file). This option is the default when decompressing.

       -N --name
              When compressing, always save the original file name and timestamp; this is the default. When decompressing,  restore
              the  original  file  name  and timestamp if present. This option is useful on systems which have a limit on file name
              length or when the timestamp has been lost after a file transfer.

       -q --quiet
              Suppress all warnings.

       -r --recursive
              Travel the directory structure recursively. If any of the file names specified on the command line  are  directories,
              gzip  will  descend  into  the directory and compress all the files it finds there (or decompress them in the case of
              gunzip ).

       -S .suf --suffix .suf
              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.

       --synchronous
              Use synchronous output.  With this option, gzip is less likely to lose data during a system crash, but it can be con‐
              siderably slower.

       -t --test
              Test. Check the compressed file integrity.

       -v --verbose
              Verbose. Display the name and percentage reduction for each file compressed or decompressed.

       -V --version
              Version. Display the version number and compilation options then quit.

       -# --fast --best
              Regulate  the  speed of compression using the specified digit #, where -1 or --fast indicates the fastest compression
              method (less compression) and -9 or --best indicates the slowest compression method (best compression).  The  default
              compression level is -6 (that is, biased towards high compression at expense of speed).

       --rsyncable
              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  ar‐
              chive,  the  compression 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 up‐
              date the archive structure in the area that was changed.

ADVANCED USAGE
       Multiple compressed files can be concatenated. In this case, gunzip 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). How‐
       ever, 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 transparently. gzip is designed as a comple‐
       ment to tar, not as a replacement.

ENVIRONMENT
       The obsolescent environment variable GZIP can hold a set of default options for gzip.  These options are  interpreted  first
       and  can be overwritten by explicit command line parameters.  As this can cause problems when using scripts, this feature is
       supported only for options that are reasonably likely to not cause too much harm, and gzip warns if it is used.   This  fea‐
       ture will be removed in a future release of gzip.

       You can use an alias or script instead.  For example, if gzip is in the directory /usr/bin you can prepend $HOME/bin to your
       PATH and create an executable script $HOME/bin/gzip containing the following:

             #! /bin/sh
             export PATH=/usr/bin
             exec gzip -9 "$@"

SEE ALSO
       znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1)

       The   gzip   file   format   is   specified   in   P.   Deutsch,   GZIP   file    format    specification    version    4.3,
       <https://www.ietf.org/rfc/rfc1952.txt>,  Internet RFC 1952 (May 1996).  The zip deflation format is specified in P. Deutsch,
       DEFLATE Compressed Data Format Specification version 1.3, <https://www.ietf.org/rfc/rfc1951.txt>,  Internet  RFC  1951  (May
       1996).

DIAGNOSTICS
       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.

       file: not in gzip format
              The file specified to gunzip has not been compressed.

       file: 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 file > recover

       file: compressed with xx bits, can only handle yy bits
              File was compressed (using LZW) by a program that could deal with more bits than the decompress code on this machine.
              Recompress the file with gzip, which compresses better and uses less memory.

       file: already has .gz suffix -- unchanged
              The file is assumed to be already compressed.  Rename the file and try again.

       file 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.

       xx.x% Percentage of the input saved by compression.
              (Relevant only for -v and -l.)

       -- 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 xx other links: unchanged
              The input file has links; it is left unchanged.  See ln(1) for more information. Use the -f flag to force compression
              of multiply-linked files.

CAVEATS
       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 gunzip for decompression, gunzip detects that there is extra trailing
       garbage after the compressed data and emits a warning by default.  You can use the --quiet option to suppress the warning.

BUGS
       The gzip format represents the input size modulo 2^32, so the --list option reports incorrect uncompressed  sizes  and  com‐
       pression  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 compressed 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 redun‐
       dant files, compress compresses better than gzip.

COPYRIGHT NOTICE
       Copyright © 1998-1999, 2001-2002, 2012, 2015-2018 Free Software Foundation, Inc.
       Copyright © 1992, 1993 Jean-loup Gailly

       Permission  is  granted to make and distribute verbatim copies of this manual provided the copyright notice and this permis‐
       sion 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 permission notice identical to this one.

       Permission  is  granted to copy and distribute translations of this manual into another language, under the above conditions
       for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

                                                               local                                                        GZIP(1)

Usage: /usr/bin/zcat [OPTION]... [FILE]...
Uncompress FILEs to standard output.

  -f, --force       force; read compressed data even from a terminal
  -l, --list        list compressed file contents
  -q, --quiet       suppress all warnings
  -r, --recursive   operate recursively on directories
  -S, --suffix=SUF  use suffix SUF on compressed files
      --synchronous synchronous output (safer if system crashes, but slower)
  -t, --test        test compressed file integrity
  -v, --verbose     verbose mode
      --help        display this help and exit
      --version     display version information and exit

With no FILE, or when FILE is -, read standard input.

Report bugs to <bug-gzip@gnu.org>.