gzip.doc

gzip源码

	  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.

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User Commands						  GZIP(1)

     -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  com-
	  pression  method  (less  compression)	 and -9	or --best
	  indicates the	slowest	compression method (best compres-
	  sion).   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 uncom-
     pressed 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:

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User Commands						  GZIP(1)

	   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 indepen-
     dently, 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
     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  invo-
     cation of the program.

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

     The gzip file format is specified in P. Deutsch,  GZIP  file
     format  specification  version  4.3,  <ftp://ftp.isi.edu/in-
     notes/rfc1952.txt>, Internet RFC 1952 (May	1996).	 The  zip
     deflation	format	is  specified in P. Deutsch, DEFLATE Com-
     pressed   Data    Format	 Specification	  version    1.3,
     <ftp://ftp.isi.edu/in-notes/rfc1951.txt>,	Internet RFC 1951
     (May 1996).

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

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User Commands						  GZIP(1)

	  machine.  Recompress the file	 with  gzip,  which  com-
	  presses 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 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
     When writing compressed data to a tape, it	is generally nec-
     essary to pad the output with zeroes up to	a block	boundary.
     When the data is read and the whole block is passed to  gun-
     zip  for  decompression,  gunzip detects that there is extra
     trailing garbage after the	compressed data	and emits a warn-
     ing  by  default. You have	to use the --quiet option to sup-
     press the warning.	This option can	be set in the GZIP  envi-
     ronment 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 gzip format represents	the 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 fol-
     lowing command to discover	a large	uncompressed file's  true

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User Commands						  GZIP(1)

     size:

	   zcat	file.gz	| wc -c

     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	 compres-
     sion than the default compression level (-6). On some highly
     redundant files, compress compresses better than gzip.

COPYRIGHT NOTICE
     Copyright (C) 1998, 1999,	2001  Free  Software  Foundation,
     Inc.
     Copyright (C) 1992, 1993 Jean-loup	Gailly

     Permission	is granted to make and distribute verbatim copies
     of	this manual provided the copyright notice and  this  per-
     mission notice are	preserved on all copies.

     Permission	 is  granted to	copy and distribute modified ver-
     sions of this manual under	the conditions for verbatim copy-
     ing, provided that	the entire resulting derived work is dis-
     tributed under the	terms of a permission notice identical to
     this one.

     Permission	is granted to copy and distribute translations of
     this manual into another language,	under  the  above  condi-
     tions  for	 modified  versions,  except that this permission
     notice may	be stated in a translation approved by the  Foun-
     dation.

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