Differences between version 14 and predecessor to the previous major change of zcat(1).
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| Newer page: | version 14 | Last edited on Tuesday, May 4, 2004 10:47:27 am | by zcat(1) | Revert |
| Older page: | version 10 | Last edited on Thursday, April 15, 2004 9:30:19 am | by AristotlePagaltzis | Revert |
@@ -1,571 +1,15 @@
-__Note:__ "zcat" is also the nickname of BruceKingsbury.
+__Note:__ "zcat" is also the nickname of BruceKingsbury. ([homepage|http://zcat.wired.net.nz/])
------
-
-GZIP
-!!!GZIP
-NAME
-SYNOPSIS
-DESCRIPTION
-OPTIONS
-ADVANCED USAGE
-ENVIRONMENT
-SEE ALSO
-DIAGNOSTICS
-CAVEATS
-BUGS
-COPYRIGHT NOTICE
----
-!!NAME
+__zcat__ is used for decompressing ".gz" zipped files and writing them to standard output. It behaves exactly as if you had typed "gzip -d -c" instead (-d decompresses, -c writes to stdout).
+On most systems, zcat is a link to gzip, and gzip behaves differently based on what name it was executed as.
-gzip, gunzip, zcat - compress or expand files
-!!SYNOPSIS
+See the
gzip(1) man page.
-
-__gzip__ [[ __-acdfhlLnNrtvV19__ ] [[__-S suffix__] [[
-''name ...'' ]__
-gunzip__ [[ __-acfhlLnNrtvV__ ] [[__-S suffix__] [[
-''name ...'' ]__
-zcat__ [[ __-fhLV__ ] [[ ''name ...'' ]
-!!DESCRIPTION
-
-
-''Gzip'' reduces the size of the named files using
-Lempel-Ziv coding (LZ77). Whenever possible, each file is
-replaced by one with the extension __.gz,__ while keeping
-the same ownership modes, access and modification times.
-(The default extension is __-gz__ for VMS, __z__ for
-MSDOS, OS/2 FAT, Windows NT FAT and Atari.) If no files are
-specified, or if a file name is
-__Gzip'' will
-only attempt to compress regular files. In particular, it
-will ignore symbolic links.
-
-
-If the compressed file name is too long for its file system,
-''gzip'' truncates it. ''Gzip'' attempts to truncate
-only the parts of the file name longer than 3 characters. (A
-part is delimited by dots.) If the name consists of small
-parts only, the longest parts are truncated. For example, if
-file names are limited to 14 characters, gzip.msdos.exe is
-compressed to gzi.msd.exe.gz. Names are not truncated on
-systems which do not have a limit on file name
-length.
-
-
-By default, ''gzip'' keeps the original file name and
-timestamp in the compressed file. These are used when
-decompressing the file with the __-N__ option. This is
-useful when the compressed file name was truncated or when
-the time stamp was not preserved after a file
-transfer.
-
-
-Compressed files can be restored to their original form
-using ''gzip -d'' or ''gunzip'' or ''zcat.'' If the
-original name saved in the compressed file is not suitable
-for its file system, a new name is constructed from the
-original one to make it legal.
-
-
-''gunzip'' takes a list of files on its command line and
-replaces each file whose name ends with .gz, -gz, .z, -z, _z
-or .Z and which begins with the correct magic number with an
-uncompressed file without the original extension.
-''gunzip'' also recognizes the special extensions
-__.tgz__ and __.taz__ as shorthands for __.tar.gz__
-and __.tar.Z__ respectively. When compressing,
-''gzip'' uses the __.tgz__ extension if necessary
-instead of truncating a file with a __.tar__
-extension.
-
-
-''gunzip'' can currently decompress files created by
-''gzip, zip, compress, compress -H'' or ''pack.'' The
-detection of the input format is automatic. When using the
-first two formats, ''gunzip'' checks a 32 bit CRC. For
-''pack, gunzip'' checks the uncompressed length. The
-standard ''compress'' format was not designed to allow
-consistency checks. However ''gunzip'' is sometimes able
-to detect a bad .Z file. If you get an error when
-uncompressing a .Z file, do not assume that the .Z file is
-correct simply because the standard ''uncompress'' does
-not complain. This generally means that the standard
-''uncompress'' does not check its input, and happily
-generates garbage output. The SCO compress -H format (lzh
-compression method) does not include a CRC but also allows
-some consistency checks.
-
-
-Files created by ''zip'' can be uncompressed by gzip only
-if they have a single member compressed with the 'deflation'
-method. This feature is only intended to help conversion of
-tar.zip files to the tar.gz format. To extract zip files
-with several members, use ''unzip'' instead of
-''gunzip.''
-
-
-''zcat'' is identical to ''gunzip'' __-c.__ (On
-some systems, ''zcat'' may be installed as ''gzcat''
-to preserve the original link to ''compress.) zcat''
-uncompresses either a list of files on the command line or
-its standard input and writes the uncompressed data on
-standard output. ''zcat'' will uncompress files that have
-the correct magic number whether they have a __.gz__
-suffix or not.
-
-
-''Gzip'' uses the Lempel-Ziv algorithm used in ''zip''
-and PKZIP. The amount of compression obtained depends on the
-size of the input and the distribution of common substrings.
-Typically, text such as source code or English is reduced by
-60-70%. Compression is generally much better than that
-achieved by LZW (as used in ''compress''), Huffman coding
-(as used in ''pack''), or adaptive Huffman coding
-(''compact'').
-
-
-Compression is always performed, even if the compressed file
-is slightly larger than the original. The worst case
-expansion is a few bytes for the gzip file header, plus 5
-bytes every 32K block, or an expansion ratio of 0.015% for
-large files. Note that the actual number of used disk blocks
-almost never increases. ''gzip'' preserves the mode,
-ownership and timestamps of files when compressing or
-decompressing.
-!!OPTIONS
-
-
-__-a --ascii__
-
-
-Ascii text mode: convert end-of-lines using local
-conventions. This option is supported only on some non-Unix
-systems. For MSDOS, CR LF is converted to LF when
-compressing, and LF is converted to CR LF when
-decompressing.
-
-
-__-c --stdout --to-stdout__
-
-
-Write output on standard output; keep original files
-unchanged. If there are several input files, the output
-consists of a sequence of independently compressed members.
-To obtain better compression, concatenate all input files
-before compressing them.
-
-
-__-d --decompress --uncompress__
-
-
-Decompress.
-
-
-__-f --force__
-
-
-Force compression or decompression even if the file has
-multiple links or the corresponding file already exists, or
-if the compressed data is read from or written to a
-terminal. If the input data is not in a format recognized by
-''gzip,'' and if the option --stdout is also given, copy
-the input data without change to the standard ouput: let
-''zcat'' behave as ''cat.'' If __-f__ is not given,
-and when not running in the background, ''gzip'' prompts
-to verify whether an existing file should be
-overwritten.
-
-
-__-h --help__
-
-
-Display a help screen and quit.
-
-
-__-l --list__
-
-
-For each compressed file, list the following
-fields:
-
-
-compressed size: size of the compressed file uncompressed
-size: size of the uncompressed file ratio: compression ratio
-(0.0% if unknown) uncompressed_name: name of the
-uncompressed file
-
-
-The uncompressed size is given as -1 for files not in gzip
-format, such as compressed .Z files. To get the uncompressed
-size for such a file, you can use:
-
-
-zcat file.Z | wc -c
-
-
-In combination with the --verbose option, the following
-fields are also displayed:
-
-
-method: compression method crc: the 32-bit CRC of the
-uncompressed data date
-
-
-The compression methods currently supported are deflate,
-compress, lzh (SCO compress -H) and pack. The crc is given
-as ffffffff for a file not in gzip format.
-
-
-With --name, the uncompressed name, date and time are those
-stored within the compress file if present.
-
-
-With --verbose, the size totals and compression ratio for
-all files is also displayed, unless some sizes are unknown.
-With --quiet, the title and totals lines are not
-displayed.
-
-
-__-L --license__
-
-
-Display the ''gzip'' license and quit.
-
-
-__-n --no-name__
-
-
-When compressing, do not save the original file name and
-time stamp by default. (The original name is always saved if
-the name had to be truncated.) When decompressing, do not
-restore the original file name if present (remove only the
-''gzip'' suffix from the compressed file name) and do not
-restore the original time stamp if present (copy it from the
-compressed file). This option is the default when
-decompressing.
-
-
-__-N --name__
-
-
-When compressing, always save the original file name and
-time stamp; this is the default. When decompressing, restore
-the original file name and time stamp if present. This
-option is useful on systems which have a limit on file name
-length or when the time stamp has been lost after a file
-transfer.
-
-
-__-q --quiet__
-
-
-Suppress all warnings.
-
-
-__-r --recursive__
-
-
-Travel the directory structure recursively. If any of the
-file names specified on the command line are directories,
-''gzip'' will descend into the directory and compress all
-the files it finds there (or decompress them in the case of
-''gunzip'' ).
-
-
-__-S .suf --suffix .suf__
-
-
-Use suffix .suf instead of .gz. Any suffix can be given, but
-suffixes other than .z and .gz should be avoided to avoid
-confusion when files are transferred to other systems. A
-null suffix forces gunzip to try decompression on all given
-files regardless of suffix, as in:
-
-
-gunzip -S
-
-
-Previous versions of gzip used the .z suffix. This was
-changed to avoid a conflict with
-pack(1)''.''
-
-
-__-t --test__
-
-
-Test. Check the compressed file integrity.
-
-
-__-v --verbose__
-
-
-Verbose. Display the name and percentage reduction for each
-file compressed or decompressed.
-
-
-__-V --version__
-
-
-Version. Display the version number and compilation options
-then quit.
-
-
-__-# --fast --best__
-
-
-Regulate the speed of compression using the specified digit
-''#'', where __-1__ or __--fast__ indicates the
-fastest compression method (less compression) and __-9__
-or __--best__ indicates the slowest compression method
-(best compression). The default compression level is
-__-6__ (that is, biased towards high compression at
-expense of speed).
-!!ADVANCED USAGE
-
-
-Multiple compressed files can be concatenated. In this case,
-''gunzip'' will extract all members at once. For
-example:
-
-
-gzip -c file1
-
-
-Then
-
-
-gunzip -c foo
-
-
-is equivalent to
-
-
-cat file1 file2
-
-
-In case of damage to one member of a .gz file, other members
-can still be recovered (if the damaged member is removed).
-However, you can get better compression by compressing all
-members at once:
-
-
-cat file1 file2 | gzip
-
-
-compresses better than
-
-
-gzip -c file1 file2
-
-
-If you want to recompress concatenated files to get better
-compression, do:
-
-
-gzip -cd old.gz | gzip
-
-
-If a compressed file consists of several members, the
-uncompressed size and CRC reported by the --list option
-applies to the last member only. If you need the
-uncompressed size for all members, you can use:
-
-
-gzip -cd file.gz | wc -c
-
-
-If you wish to create a single archive file with multiple
-members so that members can later be extracted
-independently, use an archiver such as tar or zip. GNU tar
-supports the -z option to invoke gzip transparently. gzip is
-designed as a complement to tar, not as a
-replacement.
-!!ENVIRONMENT
-
-
-The environment variable __GZIP__ can hold a set of
-default options for ''gzip.'' These options are
-interpreted first and can be overwritten by explicit command
-line parameters. For example: for sh: GZIP=
-''
-
-
-On Vax/VMS, the name of the environment variable is
-GZIP_OPT, to avoid a conflict with the symbol set for
-invocation of the program.
-!!SEE ALSO
-
-
-znew(1), zcmp(1), zmore(1), zless(1), zforce(1), gzexe(1), zip(1),
-unzip(1), compress(1), pack(1), compact(1)
-
-
-The ''gzip'' file format is specified in P. Deutsch,
-GZIP file format specification version 4.3,
-____,
-Internet RFC 1952 (May 1996). The ''zip'' deflation
-format is specified in P. Deutsch, DEFLATE
-Compressed Data Format Specification version 1.3,
-____,
-Internet RFC 1951 (May 1996).
-!!DIAGNOSTICS
-
-
-Exit status is normally 0; if an error occurs, exit status
-is 1. If a warning occurs, exit status is 2.
-
-
-Usage: gzip [[-cdfhlLnNrtvV19] [[-S suffix] [[file
-...]
-
-
-Invalid options were specified on the command
-line.
-
-
-''file'': not in gzip format
-
-
-The file specified to ''gunzip'' has not been
-compressed.
-
-
-''file'': Corrupt input. Use zcat to recover some
-data.
-
-
-The compressed file has been damaged. The data up to the
-point of failure can be recovered using
-
-
-zcat ''file'' ''
-
-
-''file'': compressed with ''xx'' bits, can only handle
-''yy'' bits
-
-
-''File'' was compressed (using LZW) by a program that
-could deal with more ''bits'' than the decompress code on
-this machine. Recompress the file with gzip, which
-compresses better and uses less memory.
-
-
-''file'': already has .gz suffix -- no
-change
-
-
-The file is assumed to be already compressed. Rename the
-file and try again.
-
-
-''file'' already exists; do you wish to overwrite (y or
-n)?
-
-
-Respond
-
-
-gunzip: corrupt input
-
-
-A SIGSEGV violation was detected which usually means that
-the input file has been corrupted.
-
-
-''xx.x%'' Percentage of the input saved by
-compression.
-
-
-(Relevant only for __-v__ and __-l__.)
-
-
--- 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
-left unaltered.
-
-
--- has ''xx'' other links: unchanged
-
-
-The input file has links; it is left unchanged. See
-ln(1) for more information. Use the __-f__ flag to
-force compression of multiply-linked files.
-!!CAVEATS
-
-
-When writing compressed data to a tape, it is generally
-necessary to pad the output with zeroes up to a block
-boundary. When the data is read and the whole block is
-passed to ''gunzip'' for decompression, ''gunzip''
-detects that there is extra trailing garbage after the
-compressed data and emits a warning by default. You have to
-use the --quiet option to suppress the warning. This option
-can be set in the __GZIP__ environment variable as in:
-for sh: GZIP=
-__
-
-
-In the above example, gzip is invoked implicitly by the -z
-option of GNU tar. Make sure that the same block size (-b
-option of tar) is used for reading and writing compressed
-data on tapes. (This example assumes you are using the GNU
-version of tar.)
-!!BUGS
-
-
-The gzip format represents the the input size modulo 2^32,
-so the --list option reports incorrect uncompressed sizes
-and compression ratios for uncompressed files 4 GB and
-larger. To work around this problem, you can use the
-following command to discover a large uncompressed file's
-true size:
-
-
-zcat file.gz | wc -c
-
-
-The --list option reports sizes as -1 and crc as ffffffff if
-the compressed file is on a non seekable media.
-
-
-In some rare cases, the --best option gives worse
-compression than the default compression level (-6). On some
-highly redundant files, ''compress'' compresses better
-than ''gzip.''
-!!COPYRIGHT NOTICE
-
-
-Copyright 1998, 1999, 2001 Free Software Foundation,
-Inc.
-Copyright 1992, 1993 Jean-loup Gailly
-
-
-Permission is granted to make and distribute verbatim copies
-of this manual provided the copyright notice and this
-permission notice are preserved on all copies.
-
-
-Permission is granted to copy and distribute modified
-versions of this manual under the conditions for verbatim
-copying, provided that the entire resulting derived work is
-distributed under the terms of a permission notice identical
-to this one.
-
-
-Permission is granted to copy and distribute translations of
-this manual into another language, under the above
-conditions for modified versions, except that this
-permission notice may be stated in a translation approved by
-the Foundation.
----
-!!user comments
+!!User Comments
someone was searching for examples for zcat, so well, why disappoint?
$ ls
@@ -580,4 +24,9 @@
Probably the best example I can think of would be;
$ zcat patch-x.y.z.gz | patch -p0
Patches are usually compressed, and patch(1) doesn't have a 'compressed' switch like tar(1) does..
+
+
+Another example (make sure to have your speakers on!):
+ $ zcat /vmlinuz > /dev/audio
+(BruceKingsbury notes; this is a pointless example at best, the difference between compressed and uncompressed executable code, or /dev/urandom for that matter, piped into /dev/audio is fairly insignificant. Also; zcat: /boot/vmlinuz-2.6.5: not in gzip format)
