pack(1)                                                   pack(1)



NAME
     pack, pcat, unpack - compress and expand files

SYNOPSIS
     pack [-] [-f] file...

     pcat file...

     unpack file...

ARGUMENTS
     -    Sets an internal flag that causes the number of times
          each byte is used, its relative frequency, and the code
          for the byte to be printed on the standard output.
          Additional occurrences of - in place of file will cause
          the internal flag to be set and reset.

     -f   Forces the packing of file.  This is useful for causing
          an entire directory to be packed, even if some of the
          files will not benefit.  If pack is successful, file
          will be removed.  Packed files can be restored to their
          original form using unpack or pcat.

     file Specifies the file to be compressed or expanded.

DESCRIPTION
     pack attempts to store the specified files in a compressed
     form.  Wherever possible (and useful), each input file is
     replaced by a packed file file.z with the same access modes,
     access and modified dates, and owner as those of file.

     The pack program uses Huffman (minimum redundancy) codes on
     a byte-by-byte basis.

     The amount of compression obtained depends on the size of
     the input file and the character frequency distribution.
     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 character frequency
     distribution is very skewed, which may occur with printer
     plots or pictures.

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

     The pack program returns a value that is the number of files
     that it failed to compress.





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pack(1)                                                   pack(1)



     No packing will occur if:

          the file appears to be already packed;  the filename
          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;  the file
          is of zero length;  a file called file.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 characters to allow space for the appended .z extension.
     Directories cannot be compressed.

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

        pcat file.z

     or just:

        pcat file

     To make an unpacked copy, say nnn, of a packed file named
     file.z (without destroying file.z) use the command:

        pcat file > nnn

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

     The unpack program expands files created by pack.  For each
     file specified in the command, a search is made for a file
     called file.z (or just file, if file ends in .z).  If this
     file appears to be a packed file, 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.

     The unpack program returns a value that is the number of
     files it was unable to unpack.  Failure may occur for the
     same reasons that it may in pcat, as well as for the
     following:

        a file with the ``unpacked'' name already exists;




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pack(1)                                                   pack(1)



     if the unpacked file cannot be created.

EXAMPLES
     The command:

        pack file1

     will pack the file, file1, into the file, file1.z, then
     removes file1 if packing is successful.

FILES
     /usr/bin/pack
          Executable file
     /usr/bin/pcat
          Executable file
     /usr/bin/unpack
          Executable file
SEE ALSO
     cat(1), compact(1)




































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