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diff --git a/usr.bin/compress/compress.1 b/usr.bin/compress/compress.1 deleted file mode 100644 index 74b7348..0000000 --- a/usr.bin/compress/compress.1 +++ /dev/null @@ -1,172 +0,0 @@ -.\" Copyright (c) 1986, 1990, 1993 -.\" The Regents of the University of California. All rights reserved. -.\" -.\" This code is derived from software contributed to Berkeley by -.\" James A. Woods, derived from original work by Spencer Thomas -.\" and Joseph Orost. -.\" -.\" Redistribution and use in source and binary forms, with or without -.\" modification, are permitted provided that the following conditions -.\" are met: -.\" 1. Redistributions of source code must retain the above copyright -.\" notice, this list of conditions and the following disclaimer. -.\" 2. Redistributions in binary form must reproduce the above copyright -.\" notice, this list of conditions and the following disclaimer in the -.\" documentation and/or other materials provided with the distribution. -.\" 3. All advertising materials mentioning features or use of this software -.\" must display the following acknowledgement: -.\" This product includes software developed by the University of -.\" California, Berkeley and its contributors. -.\" 4. Neither the name of the University nor the names of its contributors -.\" may be used to endorse or promote products derived from this software -.\" without specific prior written permission. -.\" -.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND -.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE -.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE -.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE -.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL -.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS -.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) -.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT -.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY -.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF -.\" SUCH DAMAGE. -.\" -.\" @(#)compress.1 8.2 (Berkeley) 4/18/94 -.\" -.Dd April 18, 1994 -.Dt COMPRESS 1 -.Os BSD 4.3 -.Sh NAME -.Nm compress , -.Nm uncompress , -.Nm zcat -.Nd compress and expand data -.Sh SYNOPSIS -.Nm compress -.Op Fl cfv -.Op Fl b Ar bits -.Op Ar -.Nm uncompress -.Op Fl cfv -.Op Ar -.Nm zcat -.Op Ar -.Sh DESCRIPTION -.Nm Compress -reduces the size of the named files using adaptive Lempel-Ziv coding. -Each -.Ar file -is renamed to the same name plus the extension -.Dq .Z . -As many of the modification time, access time, file flags, file mode, -user ID, and group ID as allowed by permissions are retained in the -new file. -If compression would not reduce the size of a -.Ar file , -the file is ignored. -.Pp -.Nm Uncompress -restores the compressed files to their original form, renaming the -files by deleting the -.Dq .Z -extension. -.Pp -.Nm Zcat -is an alias for -.Dq "uncompress -c" . -.Pp -If renaming the files would cause files to be overwritten and the standard -input device is a terminal, the user is prompted (on the standard error -output) for confirmation. -If prompting is not possible or confirmation is not received, the files -are not overwritten. -.Pp -If no files are specified, the standard input is compressed or uncompressed -to the standard output. -If either the input and output files are not regular files, the checks for -reduction in size and file overwriting are not performed, the input file is -not removed, and the attributes of the input file are not retained. -.Pp -The options are as follows: -.Bl -tag -width Ds -.It Fl b -Specify the -.Ar bits -code limit (see below). -.It Fl c -Compressed or uncompressed output is written to the standard output. -No files are modified. -.It Fl f -Force compression of -.Ar file , -even if it is not actually reduced in size. -Additionally, files are overwritten without prompting for confirmation. -.It Fl v -Print the percentage reduction of each file. -.El -.Pp -.Nm Compress -uses a modified Lempel-Ziv algorithm. -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 -.Fl b -flag is reached (the default is 16). -.Ar Bits -must be between 9 and 16. -.Pp -After the -.Ar bits -limit is reached, -.Nm compress -periodically checks the compression ratio. -If it is increasing, -.Nm compress -continues to use the existing code dictionary. -However, if the compression ratio decreases, -.Nm compress -discards the table of substrings and rebuilds it from scratch. This allows -the algorithm to adapt to the next "block" of the file. -.Pp -The -.Fl b -flag is omitted for -.Ar uncompress -since the -.Ar 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. -.Pp -.ne 8 -The amount of compression obtained depends on the size of the -input, the number of -.Ar 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 the historical command pack), or adaptive Huffman -coding (as used in the historical command compact), and takes less -time to compute. -.Pp -The -.Nm compress -utility exits 0 on success, and >0 if an error occurs. -.Sh SEE ALSO -.Rs -.%A Welch, Terry A. -.%D June, 1984 -.%T "A Technique for High Performance Data Compression" -.%J "IEEE Computer" -.%V 17:6 -.%P pp. 8-19 -.Re -.Sh HISTORY -The -.Nm -command appeared in -.Bx 4.3 . |