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 +==== Manuel de la commande "​gzip"​ ====
 +
 +<​code>​
 +GZIP(1) ​                                                 General Commands Manual ​                                                ​GZIP(1)
 +
 +
 +
 +NAME
 +       gzip, gunzip, zcat - compress or expand files
 +
 +SYNOPSIS
 +       gzip [ -acdfhklLnNrtvV19 ] [--rsyncable] [-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 -gz for VMS,
 +       ​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 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, 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 time stamp 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  com‐
 +       ​pressed 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  rec‐
 +       ​ognizes ​ 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 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 compress 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 uncom‐
 +       press 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 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 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 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 adaptive Huffman cod‐
 +       ing (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  com‐
 +       ​pressing or decompressing.
 +
 +OPTIONS
 +       -a --ascii
 +              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 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 compress‐
 +              ing 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 existing file should be overwrit‐
 +              ten.
 +
 +       -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: time stamp 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 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 gzip suf‐
 +              fix  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.
 +
 +       -N --name
 +              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.
 +
 +       -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 ).
 +
 +       ​--rsyncable
 +              While  compressing, ​ synchronize ​ the  output occasionally based on the input. ​ This increases size by less than 1 percent
 +              most cases, but means that the rsync(1) program can take advantage of similarities in the uncompressed input when synchro‐
 +              nizing two files compressed with this flag.  gunzip cannot tell the difference between a compressed file created with this
 +              option, and one created without it.
 +
 +       -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.
 +
 +       -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).
 +
 +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 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 complement to
 +       tar, not as a replacement.
 +
 +ENVIRONMENT
 +       The environment variable GZIP can hold a set of default options for gzip.  These options are interpreted first and can  be  over‐
 +       ​written by explicit command line parameters. For example:
 +             for sh:    GZIP="​-8v --name";​ export GZIP
 +             for csh:   ​setenv GZIP "-8v --name"​
 +             for MSDOS: set GZIP=-8v --name
 +
 +       ​On ​ Vax/VMS, the name of the environment variable is GZIP_OPT, to avoid a conflict with the symbol set for invocation of the pro‐
 +       gram.
 +
 +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,
 +       <​http://​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, <​http://​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 -- no change
 +              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 have to use the --quiet option to suppress the warning. This option can
 +       be set in the GZIP environment variable as in:
 +         for sh:  GZIP="​-q" ​ tar -xfz --block-compress /dev/rst0
 +         for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
 +
 +       In the above example, gzip is invoked implicitly by the -z option of GNU tar. Make sure that the same block size  (-b  option ​ of
 +       tar) is used for reading and writing compressed data on tapes. ​ (This example assumes you are using the GNU version of tar.)
 +
 +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 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 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)
 +
 +</​code>​
  
  • man_de_gzip.txt
  • Dernière modification: 2016/03/30 15:33
  • (modification externe)