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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-15 19:43:11 +0000 |
commit | fc22b3d6507c6745911b9dfcc68f1e665ae13dbc (patch) | |
tree | ce1e3bce06471410239a6f41282e328770aa404a /upstream/opensuse-tumbleweed/man1/compress.1 | |
parent | Initial commit. (diff) | |
download | manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.tar.xz manpages-l10n-fc22b3d6507c6745911b9dfcc68f1e665ae13dbc.zip |
Adding upstream version 4.22.0.upstream/4.22.0
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'upstream/opensuse-tumbleweed/man1/compress.1')
-rw-r--r-- | upstream/opensuse-tumbleweed/man1/compress.1 | 295 |
1 files changed, 295 insertions, 0 deletions
diff --git a/upstream/opensuse-tumbleweed/man1/compress.1 b/upstream/opensuse-tumbleweed/man1/compress.1 new file mode 100644 index 00000000..a1270e51 --- /dev/null +++ b/upstream/opensuse-tumbleweed/man1/compress.1 @@ -0,0 +1,295 @@ +.TH COMPRESS 1 local +.SH NAME +compress, uncompress, zcat \- compress and expand data +.SH SYNOPSIS +.ll +8 +.B compress +[ +.B \-f +] [ +.B \-k +] [ +.B \-v +] [ +.B \-c +] [ +.B \-V +] [ +.B \-r +] [ +.B \-b +.I bits +] [ +.B \-\- +] [ +.I "name \&..." +] +.ll -8 +.br +.B uncompress +[ +.B \-f +] [ +.B \-k +] [ +.B \-v +] [ +.B \-c +] [ +.B \-V +] [ +.B \-\- +] [ +.I "name \&..." +] +.br +.B zcat +[ +.B \-V +] [ +.B \-\- +] [ +.I "name \&..." +] +.SH DESCRIPTION +.I Compress +reduces the size of the named files using adaptive Lempel\-Ziv coding. +Whenever possible, +each file is replaced by one with the extension +.B "\&.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. +.I Compress +will only attempt to compress regular files. +In particular, it will ignore symbolic links. If a file has multiple +hard links, +.I compress +will refuse to compress it unless the +.B \-f +flag is given. +.PP +If +.B \-f +is not given and +.I compress +is run in the foreground, +the user is prompted as to whether an existing file should be overwritten. +.PP +Compressed files can be restored to their original form using +.I uncompress +or +.I zcat. +.PP +.I uncompress +takes a list of files on its command line and replaces each +file whose name ends with +.B "\&.Z" +and which begins with the correct magic number with an uncompressed +file without the +.B "\&.Z." +The uncompressed file will have the mode, ownership and +timestamps of the compressed file. +.PP +The +.B \-k +option makes +.I compress/uncompress +keep the input files instead of automatically removing them. +.PP +The +.B \-c +option makes +.I compress/uncompress +write to the standard output; no files are changed. +.PP +.I zcat +is identical to +.I uncompress +.B \-c. +.I zcat +uncompresses either a list of files on the command line or its +standard input and writes the uncompressed data on standard output. +.I zcat +will uncompress files that have the correct magic number whether +they have a +.B "\&.Z" +suffix or not. +.PP +If the +.B \-r +flag is specified, +.I compress +will operate recursively. If any of the file names specified on the command +line are directories, +.I compress +will descend into the directory and compress all the files it finds there. +When compressing, any files already compressed will be ignored, and when +decompressing, any files already decompressed will be ignored. +.PP +The +.B \-V +flag tells each of these programs to print its version and patchlevel, +along with any preprocessor flags specified during compilation, on +stderr before doing any compression or uncompression. +.PP +.I Compress +uses the modified Lempel\-Ziv algorithm popularized in +"A Technique for High Performance Data Compression", +Terry A. Welch, +.I "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 \-b +flag is reached (default 16). +.I Bits +must be between 9 and 16. The default can be changed in the source to allow +.I compress +to be run on a smaller machine. +.PP +After the +.I bits +limit is attained, +.I compress +periodically checks the compression ratio. If it is increasing, +.I compress +continues to use the existing code dictionary. However, +if the compression ratio decreases, +.I 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 +Note that the +.B \-b +flag is omitted for +.I uncompress, +since the +.I 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 +.I 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 +.IR pack ), +or adaptive Huffman coding +.RI ( compact ), +and takes less time to compute. +.PP +Under the +.B \-v +option, +a message is printed yielding the percentage of +reduction for each file compressed. +.PP +.B \-\- +may be used to halt option parsing and force all remaining arguments to be +treated as paths. +.SH "DIAGNOSTICS" +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. +.PP +Usage: compress [\-dfvcVr] [\-b maxbits] [file ...] +.in +8 +Invalid options were specified on the command line. +.in -8 +Missing maxbits +.in +8 +Maxbits must follow +.BR \-b \. +.in -8 +.IR file : +not in compressed format +.in +8 +The file specified to +.I uncompress +has not been compressed. +.in -8 +.IR file : +compressed with +.I xx +bits, can only handle +.I yy +bits +.in +8 +.I File +was compressed by a program that could deal with +more +.I bits +than the compress code on this machine. +Recompress the file with smaller +.IR bits \. +.in -8 +.IR file : +already has .Z suffix \-\- no change +.in +8 +The file is assumed to be already compressed. +Rename the file and try again. +.in -8 +.IR file : +filename too long to tack on .Z +.in +8 +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. +.in -8 +.I file +already exists; do you wish to overwrite (y or n)? +.in +8 +Respond "y" if you want the output file to be replaced; "n" if not. +.in -8 +uncompress: corrupt input +.in +8 +A SIGSEGV violation was detected which usually means that the input file has +been corrupted. +.in -8 +Compression: +.I "xx.xx%" +.in +8 +Percentage of the input saved by compression. +(Relevant only for +.BR \-v \.) +.in -8 +\-\- not a regular file or directory: ignored +.in +8 +When the input file is not a regular file or directory, +(e.g. a symbolic link, socket, FIFO, device file), it is +left unaltered. +.in -8 +\-\- has +.I xx +other links: unchanged +.in +8 +The input file has links; it is left unchanged. See +.IR ln "(1)" +for more information. Use the +.B \-f +flag to force compression of multiply\-linked files. +.in -8 +\-\- file unchanged +.in +8 +No savings is achieved by +compression. The input remains virgin. +.in -8 +.SH "BUGS" +Although compressed files are compatible between machines with large memory, +.BR \-b \12 +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.) +.SH "SEE ALSO" +.BR pack (1), +.BR compact (1) |