gzip, gunzip, gzcat - compress or expand files

     gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ... ]
     gunzip [ -acfhlLnNrtvV ] [-S suffix] [ name ... ]
     gzcat [ -fhLV ] [ name ... ]

     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 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, _z or .Z 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 format is automatic.
     When using the first two formats, gunzip checks a 32 bit CRC.  For  pack,
     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  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 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 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.


     -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 compressing them.

     -d --decompress --uncompress

     -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 ouput: 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.

     -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 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

     -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 ).

     -S .suf --suffix .suf
          Use suffix .suf instead  of  .gz.  Any  suffix  can  be  given,  but
          suffixes  other than .z and .gz should be avoided to avoid confusion
          when files are transferred to other systems.  A null  suffix  forces
          gunzip  to   try  decompression  on  all  given  files regardless of
          suffix, as in:

              gunzip -S "" *       (*.* for MSDOS)

          Previous versions of gzip used the .z suffix. This  was  changed  to
          avoid a conflict with pack(1).

     -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

     -# --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).

     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

           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,

           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.

     The 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. 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 program.

     znew(1),  zcmp(1),  zmore(1),  zforce(1),  gzexe(1),  zip(1),   unzip(1),
     compress(1), pack(1), compact(1)

     Exit status is normally 0; if an error occurs, exit status  is  1.  If  a
     warning occurs, exit status is 2.

     Usage: gzip [-cdfhlLnNrtvV19] [-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
     gunzip: corrupt input
             A SIGSEGV violation was detected which  usually  means  that  the
             input file has been corrupted.
             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.

     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.)

     The --list option reports incorrect sizes if  they  exceed  2  gigabytes.
     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.