# uncompress(1) - man - phpMan

[GZIP(1)](https://www.chedong.com/phpMan.php/man/GZIP/1/markdown)                                General Commands Manual                               [GZIP(1)](https://www.chedong.com/phpMan.php/man/GZIP/1/markdown)



## 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 symbolic links.

       If the compressed file name is too long for its file system, _gzip_  truncates  it.   _Gzip_  at‐
       tempts  to truncate only the parts of the file name longer than 3 characters.  (A part is de‐
       limited 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, _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 (ignoring case) and which begins with the correct magic  number  with
       an  uncompressed file without the original extension.  _gunzip_ also recognizes the special ex‐
       tensions **.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 format is automatic.  When using the  first  two  formats,  _gunzip_
       checks  a  32  bit CRC. For _pack_ and _gunzip_ checks the uncompressed length. The standard _com__‐
       _press_ format was not designed to allow consistency checks. However _gunzip_ is  sometimes  able
       to detect a bad .Z file. If you get an error when uncompressing a .Z file, do not assume that
       the .Z file is correct simply because the standard _uncompress_ does not complain. This  gener‐
       ally  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 _compress_.)  _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 uncom‐
       press 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 input and the distribution 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 _compress_), Huffman coding (as used in _pack_), or adap‐
       tive 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 ev‐
       ery 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 time‐
       stamps of files when compressing or decompressing.

## OPTIONS
### -a --ascii
              Ascii text mode: convert end-of-lines using local conventions.  This  option  is  sup‐
              ported  only  on  some non-Unix systems. For MSDOS, CR LF is converted to LF when com‐
              pressing, 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 consists 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  corre‐
              sponding  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 existing 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 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: 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 com‐
              press 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 dis‐
              played.

### -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  de‐
              fault.  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 de‐
              riving 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 considerably slower.

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

### -v --verbose
              Verbose.  Display the name and percentage reduction for each file compressed or decom‐
              pressed.

### -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**  in‐
              dicates  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 archive, 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 update 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). However, you can get better compression by compressing  all  mem‐
       bers 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  op‐
       tion to invoke gzip transparently. gzip is designed as a complement to tar, not as a replace‐
       ment.

## 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 feature
       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** con‐
       taining the following:

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

## SEE ALSO
       [znew(1)](https://www.chedong.com/phpMan.php/man/znew/1/markdown), [zcmp(1)](https://www.chedong.com/phpMan.php/man/zcmp/1/markdown), [zmore(1)](https://www.chedong.com/phpMan.php/man/zmore/1/markdown), [zforce(1)](https://www.chedong.com/phpMan.php/man/zforce/1/markdown), [gzexe(1)](https://www.chedong.com/phpMan.php/man/gzexe/1/markdown), [zip(1)](https://www.chedong.com/phpMan.php/man/zip/1/markdown), [unzip(1)](https://www.chedong.com/phpMan.php/man/unzip/1/markdown), [compress(1)](https://www.chedong.com/phpMan.php/man/compress/1/markdown)

       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 for‐
       mat 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  re‐
              covered 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 bet‐
              ter 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 cor‐
              rupted.

       _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)](https://www.chedong.com/phpMan.php/man/ln/1/markdown) 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  ze‐
       roes  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 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 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 redundant 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 permission notice are preserved on all copies.

       Permission  is granted to copy and distribute modified versions of this manual under the con‐
       ditions 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 lan‐
       guage, 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)](https://www.chedong.com/phpMan.php/man/GZIP/1/markdown)