


GZIP(1)							GZIP(1)


NNAAMMEE
       gzip, gunzip, zcat - compress or expand files

SSYYNNOOPPSSIISS
       ggzziipp [ --aaccddffhhllLLnnrrttvvVV1199 ] [--SS ssuuffffiixx] [ _n_a_m_e _._._.	]
       gguunnzziipp [ --aaccffhhllLLnnrrttvvVV ] [--SS ssuuffffiixx] [ _n_a_m_e _._._.  ]
       zzccaatt [ --ffhhLLVV ] [ _n_a_m_e _._._.  ]

DDEESSCCRRIIPPTTIIOONN
       _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 ..ggzz,, while keeping the same own-
       ership modes, access and modification times.  (The default
       extension  is  --ggzz  for	VMS,  zz	for  MSDOS, OS/2 FAT and
       Atari.)	If no files are specified, the standard input  is
       compressed to the standard output.  _G_z_i_p will only attempt
       to compress regular files.  In particular, it will  ignore
       symbolic links.

       If the new file name is too long for its file system, _g_z_i_p
       truncates it and keeps the original file name in the  com-
       pressed file.  _G_z_i_p attempts to truncate only the parts of
       the file name longer than 3 characters.	(A part is delim-
       ited  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 com-
       pressed to gzi.msd.exe.gz.  Names  are  not  truncated  on
       systems which do not have a limit on file name length.

       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 ..ttggzz and
       ..ttaazz as shorthands for ..ttaarr..ggzz  and  ..ttaarr..ZZ  respectively.
       When  compressing,  _g_z_i_p uses the ..ttggzz extension if neces-
       sary instead of truncating a file with a ..ttaarr 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  for-
       mats,  _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



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GZIP(1)							GZIP(1)


       _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 compres-
       sion 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  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 --cc..  (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 uncom-
       press files that have the  correct  magic  number  whether
       they have a ..ggzz 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 distribution of common substrings.  Typ-
       ically, 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.


OOPPTTIIOONNSS
       --aa ----aasscciiii
	      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.

       --cc ----ssttddoouutt ----ttoo--ssttddoouutt
	      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.





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GZIP(1)							GZIP(1)


       --dd ----ddeeccoommpprreessss ----uunnccoommpprreessss
	      Decompress.

       --ff ----ffoorrccee
	      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 _g_z_i_p_, and if the
	      option --stdout is also given, copy the input  data
	      without  change  to  the	standard  ouput: let _z_c_a_t
	      behave as _c_a_t_.  If --ff is not given,  and	when  not
	      running  in  the background, _g_z_i_p prompts to verify
	      whether an existing file should be overwritten.

       --hh ----hheellpp
	      Display a help screen and quit.

       --ll ----lliisstt
	      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  fol-
	      lowing 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  --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.





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GZIP(1)							GZIP(1)


       --LL ----lliicceennssee
	      Display the _g_z_i_p license and quit.

       --nn ----nnoo--nnaammee
	      When compressing, do not	save  the  original  file
	      name by default. (The original name is always saved
	      if the name had to be truncated.) When  decompress-
	      ing,  do not restore the original file name if pre-
	      sent: remove only the _g_z_i_p  suffix  from	the  com-
	      pressed file name.

       --qq ----qquuiieett
	      Suppress all warnings.

       --rr ----rreeccuurrssee
	      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 ).

       --SS ..ssuuff ----ssuuffffiixx ..ssuuff
	      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 trans-
	      ferred to other.	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 _p_a_c_k(1)_.

       --tt ----tteesstt
	      Test. Check the compressed file integrity.

       --vv ----vveerrbboossee
	      Verbose.	Display the name and percentage reduction
	      for each file compressed or decompressed.

       --VV ----vveerrssiioonn
	      Version. Display the version number and compilation
	      options then quit.

       --## ----ffaasstt ----bbeesstt
	      Regulate	the speed of compression using the speci-
	      fied digit _#, where  --11  or  ----ffaasstt  indicates  the
	      fastest  compression  method (less compression) and
	      --99 or  ----bbeesstt  indicates	the  slowest  compression
	      method (optimal compression).  The default compres-
	      sion level is --66 (that is, biased towards high com-
	      pression at expense of speed).




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GZIP(1)							GZIP(1)


AADDVVAANNCCEEDD UUSSAAGGEE
       Multiple	compressed  files  can	be concatenated. In this
       case, _g_u_n_z_i_p will extract all members at once.  For  exam-
       ple:

	     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 mem-
       bers can still be recovered  (if	the  damaged  member  is
       removed).  However, you can get better compression by com-
       pressing 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:

	     zcat 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.

EENNVVIIRROONNMMEENNTT
       The  environment	variable  GGZZIIPP 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="-8 -v"; export GZIP
	     for csh:	setenv GZIP "-8 -v"
	     for MSDOS: set GZIP=-8 -v

       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.

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

DDIIAAGGNNOOSSTTIICCSS
       Exit status is normally 0; if an error occurs, exit status



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GZIP(1)							GZIP(1)


       is 1. If a warning occurs, exit status is 2.

       Usage: gzip [-cdfhlLnrtvV19] [-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 com-
	       pressed.
       _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 file > 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.  Recompress 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 --vv and --ll.)
       -- 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 --ff flag to
	       force compression of multiply-linked files.

CCAAVVEEAATTSS
       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 GGZZIIPP environment variable as in:
	   for sh:    GZIP="-q"	tar xfz /dev/rmt/datn
	   for csh:   (setenv GZIP "-q"; tar xfz /dev/rmt/datn)

       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.



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GZIP(1)							GZIP(1)


BBUUGGSS
       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.




















































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