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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 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
       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 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,
       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:


       tab()    allbox;    cw(2.750000i)|     cw(2.750000i)     lw(2.750000i)|
       lw(2.750000i).    ATTRIBUTE   TYPEATTRIBUTE  VALUE  AvailabilitySUNWesu
       CSIEnabled Interface StabilityStandard


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 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)