
     NAME
	  compress, uncompress, zcat - compress and expand data

     SYYNOPSIS
	  compress [ -f ] [ -v ] [ -c ] [ -V ] [ -b <bits> ] [ name ... ]
	  uncompress [ -f ] [ -v ] [ -c ] [ -V ] [ name ... ]
	  zcat [ -V ] [ name ... ]

	  NOTE:  These three execuatbles are exactly the same, simply named
	  differently causing different default action.

     DESCRIPTION
	  Compress reduces the size of the named files using adaptive
	  Lempel-Ziv coding.  Whenever possible, each file is replaced by
	  one with the extension .Z , while keeping the same ownership
	  modes, access and modification times.  If no files are specified,
	  the standard input is compressed to the standard output.
	  Compressed files can be restored to their original form using
	  uncompress or zcat.

	  As of 1.16, AmigaUUCP's compress will decompress up to 16 bit
	  compression formats.	Default compression is 14 bits but may be
	  set to 16 bits with the '-b 16' option.  The minimum supported
	  compression bits is 12.

	  The -f option will force compression of name. This is useful for
	  compressing an entire directory, even if some of the files do not
	  actually shrink.  If -f is not given and compress is run in the
	  foreground, the user is prompted as to whether an existing file
	  should be overwritten.

	  The -c option makes compress/uncompress write to the standard
	  output; no files are changed.  The nondestructive behavior of
	  zcat is identical to that of uncompress -c.

	  Compress uses the modified Lempel-Ziv algorithm popularized in "A
	  Technique for High Performance Data Compression", Terry A. Welch,
	  IEEE Computer, vol. 17, no. 6 (June 1984), pp. 8-19.  Common
	  substrings in the file are first replaced by 9-bit codes 257 and
	  up.  When code 512 is reached, the algorithm switches to 10-bit
	  codes and continues to use more bits until the limit specified by
	  the -b flag is reached (default 16).  Bits must be between 9 and
	  16.  The default can be changed in the source to allow compress
	  to be run on a smaller machine.

	  After the bits limit is attained, compress periodically checks
	  the compression ratio.  If it is increasing, compress continues
	  to use the existing code dictionary.	However, if the compression
	  ratio decreases, compress discards the table of substrings and
	  rebuilds it from scratch.  This allows the algorithm to adapt to
	  the next "block" of the file.

	  Note that the -b flag is omitted for uncompress, since the bits
	  parameter specified during compression is encoded within the
	  output, along with a magic number to ensure that neither
	  decompression of random data nor recompression of compressed data
	  is attempted.

	  The amount of compression obtained depends on the size of the
	  input, the number of bits per code, and the distribution of
	  common substrings.  Typically, text such as source code or
	  English is reduced by 50-60%.  Compression is generally much
	  better than that achieved by Huffman coding (as used in pack), or
	  adaptive Huffman coding (compact), and takes less time to
	  compute.

	  Under the -v option, a message is printed yielding the percentage
	  of reduction for each file compressed.

	  If the -V option is specified, the current version and compile
	  options are printed on stderr.

	  Exit status is normally 0; if the last file is larger after
	  (attempted) compression, the status is 2; if an error occurs,
	  exit status is 1.

     DIAGNOSTICS
	  Usage: compress [-dfvcV] [-b maxbits] [file ...]
		  Invalid options were specified on the command line.
	  Missing maxbits
		  Maxbits must follow -b.
	  file: not in compressed format
		  The file specified to uncompress has not been
		  compressed.
	  file: compressed with xx bits, can only handle yy bits
		  File was compressed by a program that could deal
		  with more bits than the compress code on this
		  machine.  Recompress the file with smaller bits.
	  file: already has .Z suffix -- no change
		  The file is assumed to be already compressed.
		  Rename the file and try again.
	  file: filename too long to tack on .Z
		  The file cannot be compressed because its name is
		  longer than 12 characters.  Rename and try again.
		  This message does not occur on BSD systems.
	  file already exists; do you wish to overwrite (y or n)?
		  Respond "y" if you want the output file to be
		  replaced; "n" if not.
	  uncompress: corrupt input
		  A SIGSEGV violation was detected which usually means
		  that the input file has been corrupted.
	  Compression: xx.xx%
		  Percentage of the input saved by compression.
		  (Relevant only for -v.)
	  -- not a regular file: unchanged
		  When the input file is not a regular file, (e.g. a
		  directory), it is left unaltered.

	  -- has xx other links: unchanged
		  The input file has links; it is left unchanged.  See
		  ln(1) for more information.
	  -- file unchanged
		  No savings is achieved by compression.  The input
		  remains virgin.

     BUGS
	  Although compressed files are compatible between machines with
	  large memory, -b12 should be used for file transfer to
	  architectures with a small process data space (64KB or less, as
	  exhibited by the DEC PDP series, the Intel 80286, etc.)

