gzip.texi

早期freebsd实现

is read from or written to a terminal. If the input data is not in
a format recognized by @code{gzip}, and if the option --stdout is also
given, copy the input data without change to the standard ouput: let
@code{zcat} behave as @code{cat}. If @samp{-f} is not given, and
when not running in the background, @code{gzip} prompts to verify
whether an existing file should be overwritten.

@item --help
@itemx -h
Print an informative help message describing the options then quit.

@item --list
@itemx -l
For each compressed file, list the following fields:

@example
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
@end example

The uncompressed size is given as @samp{-1} for files not in @code{gzip}
format, such as compressed @samp{.Z} files. To get the uncompressed size for
such a file, you can use:

@example
zcat file.Z | wc -c
@end example

In combination with the --verbose option, the following fields are also
displayed:

@example
method: compression method (deflate,compress,lzh,pack)
crc: the 32-bit CRC of the uncompressed data
date & time: time stamp for the uncompressed file
@end example

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.

@item --license
@itemx -L
Display the @code{gzip} license then quit.

@item --no-name
@itemx -n
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 @code{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.

@item --name
@itemx -N
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.

@item --quiet
@itemx -q
Suppress all warning messages.

@item --recursive
@itemx -r
Travel the directory structure recursively. If any of the file names
specified on the command line are directories, @code{gzip} will descend
into the directory and compress all the files it finds there (or
decompress them in the case of @code{gunzip}).

@item --suffix @var{suf}
@itemx -S @var{suf}
Use suffix @samp{@var{suf}} instead of @samp{.gz}. Any suffix can be
given, but suffixes other than @samp{.z} and @samp{.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:

@example
gunzip -S "" *        (*.* for MSDOS)
@end example

Previous versions of gzip used the @samp{.z} suffix. This was changed to
avoid a conflict with @code{pack}.

@item --test
@itemx -t
Test. Check the compressed file integrity.

@item --verbose
@itemx -v
Verbose. Display the name and percentage reduction for each file compressed.

@item --version
@itemx -V
Version. Display the version number and compilation options, then quit.

@item --fast
@itemx --best
@itemx -@var{n}
Regulate the speed of compression using the specified digit @var{n},
where @samp{-1} or @samp{--fast} indicates the fastest compression
method (less compression) and @samp{--best} or @samp{-9} indicates the
slowest compression method (optimal compression).  The default
compression level is @samp{-6} (that is, biased towards high compression at
expense of speed).
@end table

@node Advanced usage, Environment, Invoking gzip, Top
@chapter Advanced usage
@cindex concatenated files

Multiple compressed files can be concatenated. In this case,
@code{gunzip} will extract all members at once. If one member is
damaged, other members might still be recovered after removal of the
damaged member. Better compression can be usually obtained if all
members are decompressed and then recompressed in a single step.

This is an example of concatenating @code{gzip} files:

@example
gzip -c file1  > foo.gz
gzip -c file2 >> foo.gz
@end example

Then

@example
gunzip -c foo
@end example

is equivalent to

@example
cat file1 file2
@end example

In case of damage to one member of a @samp{.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:

@example
cat file1 file2 | gzip > foo.gz
@end example

compresses better than

@example
gzip -c file1 file2 > foo.gz
@end example

If you want to recompress concatenated files to get better compression, do:

@example
zcat old.gz | gzip > new.gz
@end example

If a compressed file consists of several members, the uncompressed
size and CRC reported by the @samp{--list} option applies to the last member
only. If you need the uncompressed size for all members, you can use:

@example
zcat file.gz | wc -c
@end example

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 @code{tar} or @code{zip}. GNU @code{tar} supports the @samp{-z}
option to invoke @code{gzip} transparently. @code{gzip} is designed as a
complement to @code{tar}, not as a replacement.

@node Environment, Tapes, Advanced usage, Top
@chapter Environment
@cindex Environment

The environment variable @code{GZIP} can hold a set of default options for
@code{gzip}.  These options are interpreted first and can be overwritten by
explicit command line parameters.  For example:

@example
for sh:    GZIP="-8v --name"; export GZIP
for csh:   setenv GZIP "-8v --name"
for MSDOS: set GZIP=-8v --name
@end example

On Vax/VMS, the name of the environment variable is @code{GZIP_OPT}, to
avoid a conflict with the symbol set for invocation of the program.

@node Tapes, Problems, Environment, Top
@chapter Using @code{gzip} on tapes
@cindex tapes

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 @code{gunzip} for decompression,
@code{gunzip} detects that there is extra trailing garbage after the
compressed data and emits a warning by default. You have to use the
@samp{--quiet} option to suppress the warning. This option can be set in the
@code{GZIP} environment variable, as in:

@example
for sh:    GZIP="-q"  tar -xfz --block-compress /dev/rst0
for csh:   (setenv GZIP "-q"; tar -xfz --block-compress /dev/rst0)
@end example

In the above example, @code{gzip} is invoked implicitly by the @samp{-z}
option of GNU @code{tar}.  Make sure that the same block size (@samp{-b}
option of @code{tar}) is used for reading and writing compressed data on
tapes.  (This example assumes you are using the GNU version of
@code{tar}.)

@node Problems, Concept Index, Tapes, Top
@chapter Reporting Bugs
@cindex bugs

If you find a bug in @code{gzip}, please send electronic mail to
@w{@samp{jloup@@chorus.fr}} or, if this fails, to
@w{@samp{bug-gnu-utils@@prep.ai.mit.edu}}.  Include the version number,
which you can find by running @w{@samp{gzip -V}}.  Also include in your
message the hardware and operating system, the compiler used to compile
@code{gzip},
a description of the bug behavior, and the input to @code{gzip} that triggered
the bug.@refill

@node Concept Index, , Problems, Top
@unnumbered Concept Index

@printindex cp

@contents
@bye