delete trailing whitespace from control files

[debian/gzip] / gzip.doc

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 1mz 22mfor MSDOS, OS/2 FAT,  Win-
       dows  NT  FAT and Atari.)  If no files are specified, or if a file name
       is "-", the standard input is compressed to the standard output.   4mGzip0m
       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, 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 timestamp 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: timestamp 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 timestamp if present. This option is use-
              ful on systems which have a limit on file name  length  or  when
              the timestamp 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 "$@"

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<https://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<https://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, 2015-2018 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.

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