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PACK(1V)                                                              PACK(1V)



NAME
       pack, pcat, unpack - compress and expand files

SYNOPSIS
       pack [ - ] [ -f ] filename...

       pcat filename...

       unpack filename...

AVAILABILITY
       This  command  is  available  with  the  System V software installation
       option.  Refer to for information on how to install optional software.

DESCRIPTION
       pack attempts to store the specified files in a packed form using Huff-
       man  (minimum redundancy) codes on a byte-by-byte basis.  Wherever pos-
       sible (and useful), each input file filename is replaced  by  a  packed
       file  filename.z with the same access modes, access and modified dates,
       and owner as those of filename.  If pack is successful,  filename  will
       be removed.

       Packed  files  can  be  restored to their original form using unpack or
       pcat.

       The amount of compression obtained depends on the  size  of  the  input
       file and the frequency distribution of its characters.

       Because  a  decoding  tree  forms the first part of each .z file, it is
       usually not worthwhile to pack files smaller than three  blocks  unless
       the  distribution  of  characters  is very skewed.  This may occur with
       printer plots or pictures.

       Typically, large text-files are reduced to  60-75%  of  their  original
       size.   Load  modules, which use a larger character set and have a more
       uniform distribution of characters,  show  little  compression.   Their
       packed versions come in at about 90% of the original size.

       No packing will occur if:
              the file appears to be already packed
              the file name has more than 12 characters
              the file has links
              the file is a directory
              the file cannot be opened
              no disk storage blocks will be saved by packing
              a file called name.z already exists
              the .z file cannot be created
              an I/O error occurred during processing

       The  last  segment of the filename must contain no more than 12 charac-
       ters to allow space for the appended .z extension.  Directories  cannot
       be packed.

       pcat does for packed files what cat(1V) does for ordinary files, except
       that pcat cannot be used as a filter.  The specified files are unpacked
       and written to the standard output.  To view a packed file named name.z
       use:

              pcat filename.z

       or just:

              pcat filename

       To make an unpacked copy without destroying the packed version, use

              pcat filename>> newname

       Failure may occur if:
              the filename (exclusive of the .z) has more than 12 characters;
              the file cannot be opened;
              the file does not appear to be the output of pack.

       unpack expands files created by pack.  For each file filename specified
       in  the command, a search is made for a file called filename.z (or just
       filename, if filename ends in .z).   If  this  file  appears  to  be  a
       packed,  it  is replaced by its expanded version.  The new file has the
       .z suffix stripped from its name, and has the same access modes, access
       and modification dates, and owner as those of the packed file.  Failure
       may occur for the same reasons that it may in pcat, as well as for  the
       following:

       o  a file with the "unpacked" name already exists

       o  the unpacked file cannot be created.

OPTIONS
       -      Print compression statistics for the following filename or names
              on the standard output.  Subsequent `-'s between filenames  tog-
              gle statistics off and on.

       -f     Force packing of filename.  This is useful for causing an entire
              directory to be packed, even if some of the files will not bene-
              fit.

DIAGNOSTICS
       pack returns the number of files that it failed to compress.

       pcat returns the number of files it was unable to unpack.

       unpack returns the number of files it was unable to unpack.

SEE ALSO
       cat(1V)



                               17 September 1989                      PACK(1V)