pack(1)                             CLIX                             pack(1)



  NAME

    pack, pcat, unpack - Compresses/expands files

  SYNOPSIS

    pack [-] [-f] name ...

    pcat name ...

    unpack name ...

  FLAGS

    -    Sets an internal flag that determines the number of times each byte
         is used, its relative frequency, and the code for the byte that is
         displayed on stdout.  Additional occurrences of - in place of name
         will cause the internal flag to be set and reset.

    -f   Forces the packing of name.  This is useful for packing an entire
         directory even if some of the files will not benefit.

  DESCRIPTION

    The pack command attempts to store the specified files in a compressed
    form.  Wherever possible (and useful), each input file name is replaced by
    a packed file name.z with the same access modes, access and modified
    dates, and owner as those of name.  If pack is successful, name will be
    removed.  Packed files can be restored to their original form using unpack
    or pcat

    The pack command 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 60-75% 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% of the original size.

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

    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.




  2/94 - Intergraph Corporation                                              1

  pack(1)                             CLIX                             pack(1)



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

    pcat name.z

    or just:

    pcat name

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

    pcat name >nnn

    The pcat command 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 command expands files created by pack.  For each filename
    specified in the command, a search is made for a file called name.z (or
    just name, if name 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 command 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.  In addition, if a file with the ``unpacked'' name already exists
    then the unpacked file cannot be created.

  DIAGNOSTICS

    .z: write error
           An error was encountered trying to write the output file.

    : trivial file
           The file consisted of only one character repeated.

    : Huffman tree has too many levels
           This file cannot be packed.

    : no saving
           No disk storage blocks will be saved by packing.




  2                                              Intergraph Corporation - 2/94

  pack(1)                             CLIX                             pack(1)



    : filename too long
           A filename cannot be longer than 12 bytes

    : cannot open
           The file does not exist or has incorrect permissions.

    : cannot pack a directory
           A directory cannot be packed.

    : cannot pack a zero length file.
           This message is self-explanatory.

    : has links
           A file that has links cannot be packed.

    .z: already exists
           A file exists in this directory with the filename created by
           packing this file.

    .z: cannot create
           Either there is no space available or there is a permission
           problem.

    : can't change mode to mode
           This message is self-explanatory.

    : file unchanged
           No packing was done.

  EXIT VALUES

    The pack command exits with a value of 0 if successful and reports error
    numbers if not successful.

  RELATED INFORMATION

    Commands: cat(1)

















  2/94 - Intergraph Corporation                                              3