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GZIP(1)								       GZIP(1)

NAME    [Toc]    [Back]

     gzip, gunzip, gzcat - compress or expand files

SYNOPSIS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

     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 gzcat. 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

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GZIP(1)								       GZIP(1)

     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.

     gzcat is identical	to gunzip -c. (On some systems,	zcat may be installed
     as	gzcat to preserve the original link to compress.) gzcat	uncompresses
     either a list of files on the command line	or its standard	input and
     writes the	uncompressed data on standard output.  gzcat 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.

OPTIONS    [Toc]    [Back]

     -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

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GZIP(1)								       GZIP(1)

	  given, copy the input	data without change to the standard ouput: let
	  gzcat	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:

	      gzcat 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

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GZIP(1)								       GZIP(1)

     -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).

ADVANCED USAGE    [Toc]    [Back]

     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

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GZIP(1)								       GZIP(1)

	   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.

ENVIRONMENT    [Toc]    [Back]

     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    [Toc]    [Back]

     compress(1), pack(1)

DIAGNOSTICS    [Toc]    [Back]

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

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GZIP(1)								       GZIP(1)

     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 gzcat to	recover	some data.
	     The compressed file has been damaged. The data up to the point of
	     failure can be recovered using
		     gzcat 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.

CAVEATS    [Toc]    [Back]

     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    [Toc]    [Back]

     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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GZIP(1)								       GZIP(1)

     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.

									PPPPaaaaggggeeee 7777
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