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Text File
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1995-07-25
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20KB
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397 lines
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
NNNNAAAAMMMMEEEE
gzip, gunzip, zcat - compress or expand files
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ggggzzzziiiipppp [ ----aaaaccccddddffffhhhhllllLLLLnnnnrrrrttttvvvvVVVV11119999 ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
gggguuuunnnnzzzziiiipppp [ ----aaaaccccffffhhhhllllLLLLnnnnrrrrttttvvvvVVVV ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
zzzzccccaaaatttt [ ----ffffhhhhLLLLVVVV ] [ _n_a_m_e ... ]
DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
_G_z_i_p reduces the size of the named files using Lempel-Ziv
coding (LZ77). Whenever possible, each file is replaced by
one with the extension ....ggggzzzz,,,, while keeping the same ownership
modes, access and modification times. (The default
extension is ----ggggzzzz for VMS, zzzz for MSDOS, OS/2 FAT and Atari.)
If no files are specified, the standard input is compressed
to the standard output. _G_z_i_p will only attempt to compress
regular files. In particular, it will ignore symbolic
links.
If the new file name is too long for its file system, _g_z_i_p
truncates it and keeps the original file name in the
compressed file. _G_z_i_p 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.
Compressed files can be restored to their original form
using _g_z_i_p -_d or _g_u_n_z_i_p or _z_c_a_t. 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.
_g_u_n_z_i_p 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. _g_u_n_z_i_p
also recognizes the special extensions ....ttttggggzzzz and ....ttttaaaazzzz as
shorthands for ....ttttaaaarrrr....ggggzzzz and ....ttttaaaarrrr....ZZZZ respectively. When
compressing, _g_z_i_p uses the ....ttttggggzzzz extension if necessary
instead of truncating a file with a ....ttttaaaarrrr extension.
_g_u_n_z_i_p can currently decompress files created by _g_z_i_p, _z_i_p,
_c_o_m_p_r_e_s_s, _c_o_m_p_r_e_s_s -_H or _p_a_c_k. The detection of the input
format is automatic. When using the first two formats,
_g_u_n_z_i_p checks a 32 bit CRC. For _p_a_c_k, _g_u_n_z_i_p checks the
uncompressed length. The standard _c_o_m_p_r_e_s_s format was not
designed to allow consistency checks. However _g_u_n_z_i_p 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
Page 1 (printed 7/3/94)
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
is correct simply because the standard _u_n_c_o_m_p_r_e_s_s does not
complain. This generally means that the standard _u_n_c_o_m_p_r_e_s_s
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 _z_i_p 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 _u_n_z_i_p instead of _g_u_n_z_i_p.
_z_c_a_t is identical to _g_u_n_z_i_p ----cccc.... (On some systems, _z_c_a_t may
be installed as _g_z_c_a_t to preserve the original link to
_c_o_m_p_r_e_s_s.) _z_c_a_t uncompresses either a list of files on the
command line or its standard input and writes the
uncompressed data on standard output. _z_c_a_t will uncompress
files that have the correct magic number whether they have a
....ggggzzzz suffix or not.
_G_z_i_p uses the Lempel-Ziv algorithm used in _z_i_p 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 _c_o_m_p_r_e_s_s), Huffman coding (as
used in _p_a_c_k), or adaptive Huffman coding (_c_o_m_p_a_c_t).
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. _g_z_i_p preserves the mode, ownership
and timestamps of files when compressing or decompressing.
OOOOPPPPTTTTIIIIOOOONNNNSSSS
----aaaa --------aaaasssscccciiiiiiii
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.
----cccc --------ssssttttddddoooouuuutttt --------ttttoooo----ssssttttddddoooouuuutttt
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.
Page 2 (printed 7/3/94)
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
----dddd --------ddddeeeeccccoooommmmpppprrrreeeessssssss --------uuuunnnnccccoooommmmpppprrrreeeessssssss
Decompress.
----ffff --------ffffoooorrrrcccceeee
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 _g_z_i_p, and if the option --stdout
is also given, copy the input data without change to
the standard ouput: let _z_c_a_t behave as _c_a_t. If ----ffff is
not given, and when not running in the background, _g_z_i_p
prompts to verify whether an existing file should be
overwritten.
----hhhh --------hhhheeeellllpppp
Display a help screen and quit.
----llll --------lllliiiisssstttt
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 & time: time stamp for the uncompressed file
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 --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.
----LLLL --------lllliiiicccceeeennnnsssseeee
Display the _g_z_i_p license and quit.
----nnnn --------nnnnoooo----nnnnaaaammmmeeee
Page 3 (printed 7/3/94)
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
When compressing, do not save the original file name 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 _g_z_i_p suffix from the compressed file name.
----qqqq --------qqqquuuuiiiieeeetttt
Suppress all warnings.
----rrrr --------rrrreeeeccccuuuurrrrsssseeee
Travel the directory structure recursively. If any of
the file names specified on the command line are
directories, _g_z_i_p will descend into the directory and
compress all the files it finds there (or decompress
them in the case of _g_u_n_z_i_p ).
----SSSS ....ssssuuuuffff --------ssssuuuuffffffffiiiixxxx ....ssssuuuuffff
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. A null suffix forces gunzip to try
decompression on all given files regardless of suffix,
as in:
gunzip -S "" * (*.* for MSDOS)
Previous versions of gzip used the .z suffix. This was
changed to avoid a conflict with _p_a_c_k(1).
----tttt --------tttteeeesssstttt
Test. Check the compressed file integrity.
----vvvv --------vvvveeeerrrrbbbboooosssseeee
Verbose. Display the name and percentage reduction for
each file compressed or decompressed.
----VVVV --------vvvveeeerrrrssssiiiioooonnnn
Version. Display the version number and compilation
options then quit.
----#### --------ffffaaaasssstttt --------bbbbeeeesssstttt
Regulate the speed of compression using the specified
digit #, where ----1111 or --------ffffaaaasssstttt indicates the fastest
compression method (less compression) and ----9999 or --------bbbbeeeesssstttt
indicates the slowest compression method (optimal
compression). The default compression level is ----6666
(that is, biased towards high compression at expense of
speed).
AAAADDDDVVVVAAAANNNNCCCCEEEEDDDD UUUUSSSSAAAAGGGGEEEE
Multiple compressed files can be concatenated. In this case,
_g_u_n_z_i_p will extract all members at once. For example:
Page 4 (printed 7/3/94)
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
gzip -c file1 > foo.gz
gzip -c file2 >> foo.gz
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 > foo.gz
compresses better than
gzip -c file1 file2 > foo.gz
If you want to recompress concatenated files to get better
compression, do:
zcat old.gz | gzip > new.gz
EEEENNNNVVVVIIIIRRRROOOONNNNMMMMEEEENNNNTTTT
The environment variable GGGGZZZZIIIIPPPP can hold a set of default
options for _g_z_i_p. These options are interpreted first and
can be overwritten by explicit command line parameters. For
example:
for sh: GZIP="-8 -v"; export GZIP
for csh: setenv GZIP "-8 -v"
for MSDOS: set GZIP=-8 -v
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.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1),
unzip(1), compress(1), pack(1), compact(1)
DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
Exit status is normally 0; if an error occurs, exit status
is 1. If a warning occurs, exit status is 2.
Usage: gzip [-cdfhlLnrtvV19] [-S suffix] [file ...]
Invalid options were specified on the command line.
_f_i_l_e: not in gzip format
The file specified to _g_u_n_z_i_p has not been
compressed.
Page 5 (printed 7/3/94)
GGGGZZZZIIIIPPPP((((1111)))) UUUUNNNNIIIIXXXX SSSSyyyysssstttteeeemmmm VVVV ((((llllooooccccaaaallll)))) GGGGZZZZIIIIPPPP((((1111))))
_f_i_l_e: 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 > recover
_f_i_l_e: compressed with _x_x bits, can only handle _y_y bits
_F_i_l_e was compressed (using LZW) by a program that
could deal with more _b_i_t_s than the decompress code
on this machine. Recompress the file with gzip,
which compresses better and uses less memory.
_f_i_l_e: already has .gz suffix -- no change
The file is assumed to be already compressed.
Rename the file and try again.
_f_i_l_e already exists; do you wish to overwrite (y or n)?
Respond "y" if you want the output file to be
replaced; "n" if not.
gunzip: corrupt input
A SIGSEGV violation was detected which usually means
that the input file has been corrupted.
_x_x._x%
Percentage of the input saved by compression.
(Relevant only for ----vvvv and ----llll.)
-- 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 _x_x other links: unchanged
The input file has links; it is left unchanged. See
_l_n(1) for more information. Use the ----ffff flag to force
compression of multiply-linked files.
CCCCAAAAVVVVEEEEAAAATTTTSSSS
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 _g_u_n_z_i_p for decompression, _g_u_n_z_i_p 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 GGGGZZZZIIIIPPPP environment variable as in:
for sh: GZIP="-q" tar xfz /dev/rmt/datn
for csh: (setenv GZIP "-q"; tar xfz /dev/rmt/datn)
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.
BBBBUUUUGGGGSSSS
The --list option reports incorrect sizes if they exceed 2
gigabytes. The --list option reports sizes as -1 and crc as
ffffffff if the compressed file is on a non seekable media.
Page 6 (printed 7/3/94)