gzip.1

gzip源码

truncated.) When decompressing, do not restore the original file name
if present (remove only the
.I 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.
.TP
.B \-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.
.TP
.B \-q --quiet
Suppress all warnings.
.TP
.B \-r --recursive
Travel the directory structure recursively. If any of the file names
specified on the command line are directories,
.I gzip
will descend into the directory and compress all the files it finds there
(or decompress them in the case of
.I gunzip
).
.TP
.B \-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 "" *       (*.* for MSDOS)

Previous versions of gzip used
the .z suffix. This was changed to avoid a conflict with
.IR pack "(1)".
.TP
.B \-t --test
Test. Check the compressed file integrity.
.TP
.B \-v --verbose
Verbose. Display the name and percentage reduction for each file compressed
or decompressed.
.TP
.B \-V --version
Version. Display the version number and compilation options then quit.
.TP
.B \-# --fast --best
Regulate the speed of compression using the specified digit
.IR # ,
where
.B \-1
or
.B \-\-fast
indicates the fastest compression method (less compression)
and
.B \-9
or
.B \-\-best
indicates the slowest compression method (best compression).
The default compression level is
.BR \-6
(that is, biased towards high compression at expense of speed).
.SH "ADVANCED USAGE"
Multiple compressed files can be concatenated. In this case,
.I gunzip
will extract all members at once. For example:

      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:

      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.
.SH "ENVIRONMENT"
The environment variable
.B GZIP
can hold a set of default options for
.I gzip.
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.
.SH "SEE ALSO"
znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1),
pack(1), compact(1)
.PP
The
.I gzip
file format is specified in P. Deutsch, \s-1GZIP\s0 file format
specification version 4.3,
.BR <ftp://ftp.isi.edu/in-notes/rfc1952.txt> ,
Internet RFC 1952 (May 1996).
The
.I zip
deflation format is specified in P. Deutsch, \s-1DEFLATE\s0 Compressed
Data Format Specification version 1.3,
.BR <ftp://ftp.isi.edu/in-notes/rfc1951.txt> ,
Internet RFC 1951 (May 1996).
.SH "DIAGNOSTICS"
Exit status is normally 0;
if an error occurs, exit status is 1. If a warning occurs, exit status is 2.
.TP
Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
Invalid options were specified on the command line.
.TP
\fIfile\fP\^: not in gzip format
The file specified to
.I gunzip
has not been compressed.
.TP
\fIfile\fP\^: 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 \fIfile\fP > recover
.TP
\fIfile\fP\^: compressed with \fIxx\fP bits, can only handle \fIyy\fP bits
.I File
was compressed (using LZW) by a program that could deal with
more
.I bits
than the decompress code on this machine.
Recompress the file with gzip, which compresses better and uses
less memory.
.TP
\fIfile\fP\^: already has .gz suffix -- no change
The file is assumed to be already compressed.
Rename the file and try again.
.TP
\fIfile\fP already exists; do you wish to overwrite (y or n)?
Respond "y" if you want the output file to be replaced; "n" if not.
.TP
gunzip: corrupt input
A SIGSEGV violation was detected which usually means that the input file has
been corrupted.
.TP
\fIxx.x%\fP Percentage of the input saved by compression.
(Relevant only for
.BR \-v
and
.BR \-l \.)
.TP
-- 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.
.TP
-- has \fIxx\fP other links: unchanged
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.
.SH 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
.I gunzip
for decompression,
.I 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
.B GZIP
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.)
.SH 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,
.I compress
compresses better than
.I gzip.
.SH "COPYRIGHT NOTICE"
Copyright \(co 1998, 1999, 2001 Free Software Foundation, Inc.
.br
Copyright \(co 1992, 1993 Jean-loup Gailly
.PP
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.
.ig
Permission is granted to process this file through troff and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual).
..
.PP
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.
.PP
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.