GZIP(1)
GZIP(1)



NNAAMMEE
       gzip, gunzip, zcat - compress or expand files

SSYYNNOOPPSSIISS
       ggzziipp [
       --aaccddffhhllLLnnNNrrttvvVV1199 ]
       [--SS ssuuffffiixx] [ _n_a_m_e
       _._._.  ] gguunnzziipp [
       --aaccffhhllLLnnNNrrttvvVV ] [--SS
       ssuuffffiixx] [ _n_a_m_e _._._.  ]
       zzccaatt [ --ffhhLLVV ] [ _n_a_m_e
       _._._.  ]

DDEESSCCRRIIPPTTIIOONN
       _G_z_i_p  reduces  the  size  of  the  named
       files using Lempel-Ziv coding (LZ77).  Whenever
       possible, each file  is  replaced  by  one  with
       the extension ..ggzz,, while keeping the same
       ownership modes, access and modi‐ fication times.
       (The default extension is --ggzz for VMS,  z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.  _G_z_i_p will only attempt to compress
       regular files.  In particu‐ lar, it will ignore
       symbolic links.

       If the compressed file name is too long for its file
       system, _g_z_i_p trun‐ cates  it.   _G_z_i_p
       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, _g_z_i_p keeps the original file
       name and timestamp in the com‐ pressed  file.
       These  are used when decompressing the file with the
       --N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 _g_z_i_p _-_d or _g_u_n_z_i_p
       or _z_c_a_t_.  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.

       _g_u_n_z_i_p 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.  _g_u_n_z_i_p
       also recognizes the special extensions ..ttggzz and
       ..ttaazz as shorthands for ..ttaarr..ggzz and
       ..ttaarr..ZZ respectively.   When  compressing,
       _g_z_i_p  uses the ..ttggzz extension
       if necessary instead of truncating a file with a
       ..ttaarr extension.

       _g_u_n_z_i_p can currently decompress
       files created by _g_z_i_p_,  _z_i_p_,
       _c_o_m_p_r_e_s_s_, _c_o_m_p_r_e_s_s
       _-_H  or _p_a_c_k_.  The detection of
       the input format is automatic.  When using the
       first two formats, _g_u_n_z_i_p checks a 32
       bit CRC. For _p_a_c_k_, _g_u_n_z_i_p
       checks the uncompressed length. The standard
       _c_o_m_p_r_e_s_s format was not designed to
       allow consistency checks. However _g_u_n_z_i_p
       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  _u_n_c_o_m_p_r_e_s_s  does
       not complain. This generally means that the standard
       _u_n_c_o_m_p_r_e_s_s 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 _z_i_p 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 _z_i_p file with a
       single member, use a command like _g_u_n_z_i_p
       _<_f_o_o_._z_i_p or _g_u_n_z_i_p _-_S
       _._z_i_p _f_o_o_._z_i_p.  To extract zip
       files with  several members, use _u_n_z_i_p
       instead of _g_u_n_z_i_p_.

       _z_c_a_t  is  identical  to  _g_u_n_z_i_p
       --cc..   (On  some  systems,  _z_c_a_t may be
       installed as _g_z_c_a_t to preserve the original
       link  to  _c_o_m_p_r_e_s_s_._)   _z_c_a_t
       uncompresses either a list of files on the command line
       or its standard input and writes the uncompressed data
       on standard output.   _z_c_a_t  will uncompress
       files that have the correct magic number whether they
       have a ..ggzz suffix or not.

       _G_z_i_p uses the Lempel-Ziv algorithm used in
       _z_i_p 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  _c_o_m_p_r_e_s_s),  Huffman
       coding  (as used in _p_a_c_k), or adaptive Huffman
       coding (_c_o_m_p_a_c_t).

       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.  _g_z_i_p preserves
       the mode, ownership and timestamps of files when
       compressing or decompressing.

       The _g_z_i_p file format is specified in P. Deutsch,
       GZIP file format spec‐ ification version 4.3,
       <ftp://ftp.isi.edu/in-notes/rfc1952.txt>, Inter‐
       net RFC 1952 (May 1996).  The _z_i_p deflation
       format is specified  in  P.  Deutsch,  DEFLATE
       Compressed  Data  Format  Specification version 1.3,
       <ftp://ftp.isi.edu/in-notes/rfc1951.txt>, Internet
       RFC 1951 (May 1996).


OOPPTTIIOONNSS
       --aa ----aasscciiii
              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.

       --cc ----ssttddoouutt
       ----ttoo--ssttddoouutt
              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d ----ddeeccoommpprreessss
       ----uunnccoommpprreessss
              Decompress.

       --ff ----ffoorrccee
              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
              _g_z_i_p_, and  if  the  option --stdout
              is  also  given, copy the input data without
              change to the standard output: let _z_c_a_t
              behave  as  _c_a_t_.   If  --ff  is  not
              given,  and  when not running in the background,
              _g_z_i_p prompts to verify whether an
              existing file should be overwritten.

       --hh ----hheellpp
              Display a help screen and quit.

       --ll ----lliisstt
              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:
                  time stamp 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.

       --LL ----lliicceennssee
              Display the _g_z_i_p license and quit.

       --nn ----nnoo--nnaammee
              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 _g_z_i_p 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.

       --NN ----nnaammee
              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q ----qquuiieett
              Suppress all warnings.

       --rr ----rreeccuurrssiivvee
              Travel the directory structure recursively. If
              any of  the  file names  specified  on the
              command line are directories, _g_z_i_p will
              descend into the directory and compress all the
              files  it  finds there (or decompress them in
              the case of _g_u_n_z_i_p ).

       --SS ..ssuuff ----ssuuffffiixx
       ..ssuuff
              Use  suffix  .suf  instead  of .gz. Any suffix
              can be given, but suffixes other than .z and .gz
              should be avoided to avoid confu‐ sion when
              files are transferred to other systems.  A null
              suffix forces gunzip to  try decompression on all
              given  files  regard‐ less of suffix, as in:

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

              Previous  versions  of gzip used the .z
              suffix. This was changed to avoid a conflict
              with _p_a_c_k(1)_.

       --tt ----tteesstt
              Test. Check the compressed file integrity.

       --vv ----vveerrbboossee
              Verbose. Display the name and percentage
              reduction for each file compressed or
              decompressed.

       --VV ----vveerrssiioonn
              Version. Display the version number and
              compilation options then quit.

       --## ----ffaasstt ----bbeesstt
              Regulate the speed of compression using the
              specified  digit  _#, where  --11  or
              ----ffaasstt  indicates  the fastest
              compression method (less compression) and --99
              or ----bbeesstt indicates the  slowest
              com‐ pression  method  (best  compression).
              The default compression level is --66 (that
              is, biased towards high compression at expense
              of speed).

AADDVVAANNCCEEDD UUSSAAGGEE
       Multiple  compressed  files  can  be concatenated. In
       this case, _g_u_n_z_i_p 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.

EENNVVIIRROONNMMEENNTT
       The environment variable GGZZIIPP can hold a set  of
       default  options  for _g_z_i_p_.   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.

SSEEEE AALLSSOO
       znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1),
       zip(1), unzip(1), com‐ press(1), pack(1), compact(1)

       The _g_z_i_p file format is specified in P. Deutsch,
       GZIP file format spec‐ ification version 4.3,
       <<ffttpp::////ffttpp..iissii..eedduu//iinn--nnootteess//rrffcc11995522..ttxxtt>>,
       Inter‐ net RFC 1952 (May 1996).  The _z_i_p
       deflation format is specified  in  P.  Deutsch,  DEFLATE
       Compressed  Data  Format  Specification version 1.3,
       <<ffttpp::////ffttpp..iissii..eedduu//iinn--nnootteess//rrffcc11995511..ttxxtt>>,
       Internet RFC 1951 (May 1996).

DDIIAAGGNNOOSSTTIICCSS
       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.

       _f_i_l_e: not in gzip format
              The file specified to _g_u_n_z_i_p has
              not been compressed.

       _f_i_l_e: 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 _f_i_l_e > recover

       _f_i_l_e: compressed with _x_x bits, can only
       handle _y_y bits
              _F_i_l_e was compressed (using LZW)
              by a  program  that  could  deal with more
              _b_i_t_s than the decompress code on this
              machine.  Recom‐ press the file with gzip,
              which compresses better and uses  less memory.

       _f_i_l_e: already has .gz suffix -- no change
              The  file  is assumed to be already compressed.
              Rename the file and try again.

       _f_i_l_e 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.

       _x_x_._x_% Percentage of the input saved by
       compression.
              (Relevant only for --vv and --l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 _x_x other links: unchanged
              The  input  file has links; it is left unchanged.
              See _l_n(1) for more information. Use the
              --ff flag to force compression of multi‐
              ply-linked files.

CCAAVVEEAATTSS
       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 _g_u_n_z_i_p for
       decompression, _g_u_n_z_i_p 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  GGZZIIPP  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.)

BBUUGGSS
       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,  _c_o_m_‐
       _p_r_e_s_s compresses better than _g_z_i_p_.

CCOOPPYYRRIIGGHHTT NNOOTTIICCEE
       Copyright © 1998, 1999, 2001, 2002 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 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.



                                     local
                                     GZIP(1)
