4BSD/usr/man/cat1/compact.1

COMPACT(1)          UNIX Programmer's Manual           COMPACT(1)



NAME
     compact, uncompact, ccat - compress and uncompress files,
     and cat them

SYNOPSIS
     compact [ name ... ]
     uncompact [ name ...  ]
     ccat [ file ... ]

DESCRIPTION
     _C_o_m_p_a_c_t compresses the named files using an adaptive Huffman
     code.  If no file names are given, then the standard input
     is compacted to the standard output.  _C_o_m_p_a_c_t operates as an
     on-line algorithm.  Each time a byte is read, it is encoded
     immediately according to the current prefix code.  This code
     is an optimal Huffman code for the set of frequencies seen
     so far.  It is unnecessary to prepend a decoding tree to the
     compressed file since the encoder and the decoder start in
     the same state and stay synchronized.  Furthermore, _c_o_m_p_a_c_t
     and _u_n_c_o_m_p_a_c_t can operate as filters.  In particular,

          ... | compact | uncompact | ...

     operates as a (very slow) no-op.

     When an argument _f_i_l_e is given, it is compacted and the
     resulting file is placed in _f_i_l_e._C; _f_i_l_e is unlinked.  The
     first two bytes of the compacted file code the fact that the
     file is compacted.  This code is used to prohibit recompac-
     tion.

     The amount of compression to be expected depends on the type
     of file being compressed.  Typical values of compression
     are: Text (38%), Pascal Source (43%), C Source (36%) and
     Binary (19%).  These values are the percentages of file
     bytes reduced.

     _U_n_c_o_m_p_a_c_t restores the original file from a file compressed
     by _c_o_m_p_a_c_t. If no file names are given, then the standard
     input is uncompacted to the standard output.

     _C_c_a_t cats the original file from a file compressed by _c_o_m_-
     _p_a_c_t, without uncompressing the file.

RESTRICTION
     The last segment of the filename must contain fewer than
     thirteen characters to allow space for the appended '.C'.

FILES
     *.C       compacted file created by compact, removed by
     uncompact




Printed 11/10/80                                                1






COMPACT(1)          UNIX Programmer's Manual           COMPACT(1)



SEE ALSO
     Gallager, Robert G., "Variations on a Theme of Huffman",
     _I._E._E._E.  _T_r_a_n_s_a_c_t_i_o_n_s _o_n _I_n_f_o_r_m_a_t_i_o_n _T_h_e_o_r_y, vol. IT-24,
     no. 6, November 1978, pp. 668 - 674.

AUTHOR
     Colin L. Mc Master

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Printed 11/10/80                                                2