


      PACK(1)                     (UNIX 5.0)                    PACK(1)



      NAME
           pack, pcat, unpack - compress and expand files

      SYNTAX
           pack [ - ] 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
           .  If pack is successful, name is removed.  Packed files can
           be restored to their original form by unpack or pcat.

           Pack uses Huffman (minimum redundancy) codes on a byte-by-
           byte basis.

           -    is a request to print the number of times each byte is
                used, its relative frequency, and the code for the
                byte.  Additional uses of - in place of name will cause
                the request 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 8192 bytes, 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;



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      PACK(1)                     (UNIX 5.0)                    PACK(1)



                the .z file cannot be created;
                an I/O error occurred during processing.

           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.  The specified files are unpacked and written to the
           standard output.  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

           With no arguments, pcat unpacks the standard input, and
           therefore can be used as a filter in a pipeline:

                pcat < packedfile.z | more

           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.





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