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compress (1) ( Solaris man: Команды и прикладные программы пользовательского уровня ) compress (1) ( FreeBSD man: Команды и прикладные программы пользовательского уровня ) compress (1) ( Русские man: Команды и прикладные программы пользовательского уровня )>> compress (1) ( Linux man: Команды и прикладные программы пользовательского уровня ) compress (1) ( POSIX man: Команды и прикладные программы пользовательского уровня )Ключ compress обнаружен в базе ключевых слов.
compress, uncompress, zcat - compress and expand data (version 4.1)
reduces the size of the named files using adaptive Lempel-Ziv coding.
each file is replaced by one with the extension
while keeping the same ownership modes, access and modification times.
If no files are specified, the standard input is compressed to the
will only attempt to compress regular files.
In particular, it will ignore symbolic links. If a file has multiple
will refuse to compress it unless the
flag is given.
is not given and
is run in the foreground,
the user is prompted as to whether an existing file should be overwritten.
Compressed files can be restored to their original form using
takes a list of files on its command line and replaces each
file whose name ends with
and which begins with the correct magic number with an uncompressed
file without the
The uncompressed file will have the mode, ownership and
timestamps of the compressed file.
write to the standard output; no files are changed.
is identical to
uncompresses either a list of files on the command line or its
standard input and writes the uncompressed data on standard output.
will uncompress files that have the correct magic number whether
they have a
suffix or not.
flag is specified,
will operate recursively. If any of the file names specified on the command
line are directories,
will descend into the directory and compress all the files it finds there.
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.
uses the modified Lempel-Ziv algorithm popularized in
"A Technique for High Performance Data Compression",
Terry A. Welch,
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
flag is reached (default 16).
must be between 9 and 16. The default can be changed in the source to allow
to be run on a smaller machine.
limit is attained,
periodically checks the compression ratio. If it is increasing,
continues to use the existing code dictionary. However,
if the compression ratio decreases,
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
flag is omitted for
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
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
or adaptive Huffman coding
and takes less time to compute.
a message is printed yielding the percentage of
reduction for each file compressed.
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.
Usage: compress [-dfvcVr] [-b maxbits] [file ...]
Invalid options were specified on the command line.
Maxbits must follow
not in compressed format
The file specified to
has not been compressed.
bits, can only handle
was compressed by a program that could deal with
than the compress code on this machine.
Recompress the file with smaller
already has .Z suffix -- no change
The file is assumed to be already compressed.
Rename the file and try again.
filename too long to tack on .Z
The file cannot be compressed because its name is longer than
Rename and try again.
This message does not occur on BSD systems.
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
Percentage of the input saved by compression.
(Relevant only for
-- not a regular file or directory: ignored
When the input file is not a regular file or directory,
(e.g. a symbolic link, socket, FIFO, device file), it is
other links: unchanged
The input file has links; it is left unchanged. See
for more information. Use the
flag to force compression of multiply-linked files.
-- file unchanged
No savings is achieved by
compression. The input remains virgin.
Although compressed files are compatible between machines with large memory,
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.)
Invoking compress with a -r
flag will occasionally cause it to produce spurious error warnings of the form
"<filename>.Z already has .Z suffix - ignored"
These warnings can be ignored. See the comments in compress.c:compdir()
for an explanation.
- SEE ALSO