pack(1)     UNIX System V(Directory and File Management Utilities)      pack(1)


NAME
      pack, pcat, unpack - compress and expand files

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

      pcat name ...

      unpack name ...

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

      pack uses Huffman (minimum redundancy) codes on a byte-by-byte basis.  If
      the - argument is used, an internal flag is set 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 name will cause the internal flag to be set and reset.

      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.

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

      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;


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pack(1)     UNIX System V(Directory and File Management Utilities)      pack(1)


            the file size is over 16 MB.

      The last segment of the file name must contain no more than 12 characters
      to allow space for the appended .z extension.  Directories cannot be
      compressed.

      pcat 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
      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

      pcat returns the number of files it was unable to unpack.  Failure may
      occur if:

            the file name (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 name 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.

      Unpack 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;
            if the unpacked file cannot be created.

SEE ALSO
      cat(1), compress(1).











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