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compress(1)			 User Commands			   compress(1)

NAME
       compress,  uncompress, zcat - compress, uncompress files	or display ex-
       panded files

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

       compress	[-cfv] [-b bits] [file]

       uncompress [-cfv] [file...]

       zcat [file...]

DESCRIPTION
   compress
       The compress utility will attempt to reduce the size of the named files
       by  using  adaptive Lempel-Ziv coding. Except when the output is	to the
       standard	output,	each file will be replaced by one with	the  extension
       .Z,  while keeping the same ownership modes, change times and modifica-
       tion times. If appending	the .Z to the file  pathname  would  make  the
       pathname	 exceed	 1023  bytes,  the  command will fail. If no files are
       specified, the standard input will be compressed	to the	standard  out-
       put.

       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 cod-
       ing  (as	 used  in pack(1)) and it takes	less time to compute. The bits
       parameter 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  al-
       lowed.

   uncompress
       The uncompress utility will restore files to their original state after
       they have been compressed using the compress utility. If	no  files  are
       specified, the standard input will be uncompressed to the standard out-
       put.

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

   zcat
       The zcat	utility	will write 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:

       -c	Writes to the standard output; no files	are changed and	no  .Z
		files  are  created. 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	corre-
		sponding file.Z	file already exists. If	the -f option  is  not
		given,	and  the  process  is  not  running in the background,
		prompts	to verify whether an existing file.Z  file  should  be
		overwritten.   When  uncompressing,  does not prompt for over-
		writing	files. If the -f option	is not given, 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 given, writes a diagnostic mes-
		sage to	standard error and exits with a	status greater than 0.

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

       -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  will  result in larger, less compressed
		files.

OPERANDS
       The following operand is	supported:

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

USAGE
       See  largefile(5)  for the description of the behavior of compress, un-
       compress, 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_CTYPE,  LC_MESSAGES,	and NLSPATH.

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	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       ln(1), pack(1), attributes(5), environ(5), largefile(5),	standards(5)

DIAGNOSTICS
       Usage: compress [-fvc] [-b maxbits] [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 in-
	   put file is corrupted.

       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 unaltered.

       - - 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	uncom-
	   pressed.

       filename	too long to tack on .Z

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

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 5.10			  9 Sep	1999			   compress(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | USAGE | ENVIRONMENT VARIABLES | EXIT STATUS | ATTRIBUTES | SEE ALSO | DIAGNOSTICS | NOTES

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