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OpenSolaris 2009.06 - man page for compress (opensolaris section 1)

compress(1)				  User Commands 			      compress(1)

NAME
       compress, uncompress, zcat - compress, uncompress files or display expanded files

SYNOPSIS
       compress [-fv/] [-b bits] [file]...

       compress -c [-fv] [-b bits] [file]

       uncompress [-fv] [-c | -/] [file]...

       zcat [file]...

DESCRIPTION
   compress
       The compress utility attempts to reduce the size of the named files by using adaptive Lem-
       pel-Ziv coding. Except when the output is to the standard output, each file is replaced by
       one  with the extension .Z, while keeping the same ownership modes, change times and modi-
       fication times, ACLs, and extended attributes. The compress utility also  attempt  to  set
       the  owner  and	group of file.z to the owner and group of file, but does not fail if this
       cannot be done. If appending the .Z to the file pathname would make  the  pathname  exceed
       1023 bytes, the command fails. If no files are specified, the standard input is compressed
       to the standard output.

       The amount of compression obtained depends on the size of the input, the  number  of  bits
       per  code,  and the distribution of common substrings. Typically, text such as source code
       or English is reduced by 50-60%. Compression is generally much better than  that  achieved
       by Huffman coding (as used in pack(1)) and it takes less time to compute. The bits parame-
       ter specified during compression is encoded within the compressed file, along with a magic
       number to ensure that neither decompression of random data nor recompression of compressed
       data is subsequently allowed.

   uncompress
       The uncompress utility restores files to their original state after they  have  been  com-
       pressed	using  the  compress  utility.	If  no files are specified, the standard input is
       uncompressed to the standard output.

       This utility supports the uncompressing of any files produced by compress. For files  pro-
       duced by compress on other systems, uncompress supports 9- to 16-bit compression (see -b).

   zcat
       The  zcat  utility writes to standard output the uncompressed form of files that have been
       compressed using compress. It is the equivalent	of  uncompress-c.  Input  files  are  not
       affected.

OPTIONS
       The following options are supported:

       -b bits	  Sets the upper limit (in bits) for common substring codes. bits must be between
		  9 and 16 (16 is the default). Lowering the number of	bits  result  in  larger,
		  less compressed files.

       -c	  Writes  to  the  standard output; no files are changed and no .Z files are cre-
		  ated. The behavior of zcat is identical to that of `uncompress -c'.

       -f	  When compressing, forces compression of file, even  if  it  does  not  actually
		  reduce  the  size  of  the  file,  or  if the corresponding file.Z file already
		  exists.

		  If the -f option is not specified, and the process is not running in the  back-
		  ground,  prompts  to	verify whether an existing file should be overwritten. If
		  the response is affirmative, the existing file is overwritten. When uncompress-
		  ing,	does not prompt for overwriting files. If the -f option is not specified,
		  and the process is not running in the background, prompts to verify whether  an
		  existing  file  should  be overwritten. If the standard input is not a terminal
		  and -f is not specified, writes a diagnostic	message  to  standard  error  and
		  exits with a status greater than 0.

       -v	  Verbose.  Writes to standard error messages concerning the percentage reduction
		  or expansion of each file.

       -/	  When compressing or decompressing, copies any extended system attributes  asso-
		  ciated  with	the source file to the target file and copies any extended system
		  attributes associated with extended attributes of the source file to the corre-
		  sponding  extended  attributes associated with the target file. If any extended
		  system attributes cannot be copied, the original file is retained, a diagnostic
		  is written to stderr, and the final exit status is non-zero.

OPERANDS
       The following operand is supported:

       file    A path name of a file to be compressed by compress, uncompressed by uncompress, or
	       whose uncompressed form is written to standard out by zcat. If file is -, or if no
	       file is specified, the standard input is used.

USAGE
       See  largefile(5)  for  the  description of the behavior of compress, uncompress, and zcat
       when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

ENVIRONMENT VARIABLES
       See environ(5) for descriptions of the following environment  variables	that  affect  the
       execution  of  compress, uncompress, and zcat: LANG, LC_ALL, LC_COLLATE, LC_CTYPE, LC_MES-
       SAGES, and NLSPATH.

       Affirmative responses are processed using the extended regular expression defined for  the
       yesexpr	keyword in the LC_MESSAGES category of the user's locale. The locale specified in
       the LC_COLLATE category defines the behavior of ranges, equivalence  classes,  and  multi-
       character collating elements used in the expression defined for yesexpr. The locale speci-
       fied in LC_CTYPE determines the locale for interpretation of sequences of  bytes  of  text
       data  a	characters,  the behavior of character classes used in the expression defined for
       the yesexpr. See locale(5).

EXIT STATUS
       The following error values are returned:

       0     Successful completion.

       1     An error occurred.

       2     One or more files were not compressed because they would have increased in size (and
	     the -f option was not specified).

       >2    An error occurred.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWesu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

SEE ALSO
       ln(1),  pack(1),  fgetattr(3C),	fsetattr(3C),  attributes(5),  environ(5),  largefile(5),
       locale(5), standards(5)

DIAGNOSTICS
       Usage: compress [-fv/] [-b bits] [file... ]
       compress c [-fv] [-b bits] [file... ]

	   Invalid options were specified on the command line.

       Usage: uncompress [-fv] [-c | -/] [file]...

	   Invalid options were specified on the command line.

       Missing maxbits

	   Maxbits must follow -b, or invalid maxbits, not a numeric value.

       file: not in compressed format

	   The file specified to uncompress has not been compressed.

       file: compressed with xxbits, can only handle yybits

	   file was compressed by a program that could deal with more bits than the compress code
	   on this machine. Recompress the file with smaller bits.

       file: already has .Z 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.

       uncompress: corrupt input

	   A  SIGSEGV  violation  was  detected,  which usually means that the input file is cor-
	   rupted.

       Compression:xx.xx%

	   Percentage of the input saved by compression. (Relevant only for -v.)

       - - not a regular file: unchanged

	   When the input file is not a regular file, (such as a directory),  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.

       - - file unchanged

	   No savings are achieved by compression. The input remains uncompressed.

       - -filename too long to tack on .Z

	   The path name is too long to append the .Z suffix.

       - -cannot preserve extended attributes. file unchanged

	   Extended system attributes could not be copied.

NOTES
       Although  compressed files are compatible between machines with large memory, -b 12 should
       be used for file transfer to architectures with a small process data space (64KB or less).

       compress should be more flexible about the existence of the .Z suffix.

SunOS 5.11				   13 Mar 2008				      compress(1)


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