compress(1)							   User Commands						       compress(1)

NAME

       compress, uncompress, zcat - compress, uncompress files or display expanded 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 mod-
       ification 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 output.

       The amount of compression obtained depends on the size of the input, the number of bits per code,  and  the  distribution  of  common  sub-
       strings.  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 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 allowed.

   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 output.

       This utility supports the uncompressing of any files produced by compress. 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  equiva-
       lent 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  corresponding
		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  overwriting  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 over-
		written. If the standard input is not a terminal and -f is not given, 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.

       -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, 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 will be 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_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 input 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 uncompressed.

       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)