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IRIX Base Documentation 1998 November
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IRIX 6.5.2 Base Documentation November 1998.img
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gzip.z
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1998-10-20
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463 lines
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
NNNNAAAAMMMMEEEE
gzip, gunzip, gzcat - compress or expand files
SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
ggggzzzziiiipppp [ ----aaaaccccddddffffhhhhllllLLLLnnnnNNNNrrrrttttvvvvVVVV11119999 ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
gggguuuunnnnzzzziiiipppp [ ----aaaaccccffffhhhhllllLLLLnnnnNNNNrrrrttttvvvvVVVV ] [----SSSS ssssuuuuffffffffiiiixxxx] [ _n_a_m_e ... ]
ggggzzzzccccaaaatttt [ ----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, Windows NT
FAT and Atari.) If no files are specified, or if a file name is "-", 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 compressed file name is too long for its file system, _g_z_i_p
truncates it. _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.
By default, _g_z_i_p keeps the original file name and timestamp in the
compressed file. These are used when decompressing the file with the ----NNNN
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 _g_z_i_p -_d or
_g_u_n_z_i_p or _g_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 is correct simply because the
standard _u_n_c_o_m_p_r_e_s_s does not complain. This generally means that the
PPPPaaaaggggeeee 1111
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
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.
_g_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.) _g_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. _g_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.
----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
PPPPaaaaggggeeee 2222
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
given, copy the input data without change to the standard ouput: let
_g_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:
gzcat 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 --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.
----LLLL --------lllliiiicccceeeennnnsssseeee
Display the _g_z_i_p license and quit.
----nnnn --------nnnnoooo----nnnnaaaammmmeeee
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 _g_z_i_p 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.
PPPPaaaaggggeeee 3333
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
----NNNN --------nnnnaaaammmmeeee
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.
----qqqq --------qqqquuuuiiiieeeetttt
Suppress all warnings.
----rrrr --------rrrreeeeccccuuuurrrrssssiiiivvvveeee
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 systems. 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 (best 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:
gzip -c file1 > foo.gz
gzip -c file2 >> foo.gz
PPPPaaaaggggeeee 4444
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
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:
gzip -cd old.gz | gzip > new.gz
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.
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="-8v --name"; export GZIP
for csh: setenv GZIP "-8v --name"
for MSDOS: set GZIP=-8v --name
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
compress(1), pack(1)
DDDDIIIIAAAAGGGGNNNNOOOOSSSSTTTTIIIICCCCSSSS
Exit status is normally 0; if an error occurs, exit status is 1. If a
warning occurs, exit status is 2.
PPPPaaaaggggeeee 5555
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
Usage: gzip [-cdfhlLnNrtvV19] [-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.
_f_i_l_e: Corrupt input. Use gzcat to recover some data.
The compressed file has been damaged. The data up to the point of
failure can be recovered using
gzcat 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 --block-compress /dev/rst0
for csh: (setenv GZIP -q; tar -xfz --block-compr /dev/rst0
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.)
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.
PPPPaaaaggggeeee 6666
GGGGZZZZIIIIPPPP((((1111)))) GGGGZZZZIIIIPPPP((((1111))))
In some rare cases, the --best option gives worse compression than the
default compression level (-6). On some highly redundant files, _c_o_m_p_r_e_s_s
compresses better than _g_z_i_p.
PPPPaaaaggggeeee 7777
