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GZIP(1)			    General Commands Manual		       GZIP(1)

NAME
       gzip, gunzip, zcat - compress or	expand files

SYNOPSIS
       gzip [ -acdfhlLnNrtvV19 ] [-S suffix] [ name ...	 ]
       gunzip [	-acfhlLnNrtvV ]	[-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 modi-
       fication	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 particu-
       lar, it will ignore symbolic links.

       If the compressed file name is too long for its file system, gzip trun-
       cates  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 com-
       pressed	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 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  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.

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 con-
	      verted 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
	      Decompress.

       -f --force
	      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 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	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  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 --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 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 ).

       -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	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 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
	      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  com-
	      pression	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 transpar-
       ently. 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	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.

SEE ALSO
       znew(1),	zcmp(1), zmore(1), zforce(1), gzexe(1),	compress(1)

DIAGNOSTICS
       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
	       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 unal-
	       tered.
       -- 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 mul-
	       tiply-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  --list  option reports incorrect sizes if they exceed 2 gigabytes.
       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,  com-
       press compresses	better than gzip.

								       GZIP(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ADVANCED USAGE | ENVIRONMENT | SEE ALSO | DIAGNOSTICS | CAVEATS | BUGS

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