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Diff for /src/usr.bin/compress/compress.1 between version 1.34 and 1.35

version 1.34, 2005/07/22 09:30:51

version 1.35, 2007/01/24 10:53:43

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.Sh NAME

.Nm compress ,

.Nm uncompress ,

.Nm gzip ,

.Nm zcat

.Nm gunzip ,

.Nd compress and expand data (compress mode)

.Nm zcat ,

.Nm gzcat

.Nd compress and expand data

.Sh SYNOPSIS

.Nm compress

.Op Fl LV

.Op Fl 123456789cdfghLlNnOqrtVv

.Nm compress

.Op Fl 123456789cdfghlNnOqrtv

.Op Fl b Ar bits

.Op Fl o Ar filename

.Op Fl S Ar suffix

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.Op Fl cfhlNnqrtv

.Op Fl o Ar filename

.Op Ar

.Pp

.Nm gzip

.Op Fl LV

.Nm gzip

.Op Fl 123456789cdfghlNnOqrtv

.Op Fl b Ar bits

.Op Fl o Ar filename

.Op Fl S Ar suffix

.Op Ar

.Nm gunzip

.Op Fl cfhlNnqrtv

.Op Fl o Ar filename

.Op Ar

.Pp

.Nm zcat

.Op Fl fghqr

.Op Ar

.Nm gzcat

.Op Fl fghqr

.Op Ar

.Sh DESCRIPTION

The

.Nm compress

.Nm

and

utility

.Nm gzip

reduces the size of the named files using adaptive Lempel-Ziv coding,

utilities

in compress mode.

reduce the size of the named files using adaptive Lempel-Ziv coding.

They are functionally identical, but use different algorithms for compression.

If invoked as

.Nm gzip

.Nm compress Fl g ,

the deflate mode of compression is chosen by default;

the deflate mode of compression is chosen;

otherwise the older method of compression

see

.Pq compress mode

.Xr gzip 1

is used.

for more information.

.Pp

Each file is renamed to the same name plus the extension

Each

.Dq .Z .

.Ar file

is renamed to the same name plus the extension

.Dq .Z ,

.Dq .gz

(in deflate mode).

As many of the modification time, access time, file flags, file mode,

user ID, and group ID as allowed by permissions are retained in the

new file.

If compression would not reduce the size of a

If compression would not reduce the size of a file,

.Ar file ,

the file is ignored (unless

.Fl f

is used).

.Pp

The

.Nm uncompress

and

utility restores compressed files to their original form, renaming the

.Nm gunzip

utilities restore compressed files to their original form, renaming the

files by removing the extension (or by using the stored name if the

.Fl N

flag is specified).

When decompressing, the following extensions are recognized:

It has the ability to restore files compressed by both

.Nm

and

.Xr gzip 1 ,

recognising the following extensions:

.Dq .Z ,

.Dq -Z ,

.Dq _Z ,

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command is equivalent in functionality to

.Nm uncompress

.Fl c .

The

.Nm gzcat

command is equivalent in functionality to

.Nm gunzip

.Fl c .

.Pp

If renaming the files would cause files to be overwritten and the standard

input device is a terminal, the user is prompted (on the standard error

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The options are as follows:

.Bl -tag -width Ds

.It Fl 1...9

Use deflate scheme with compression factor of

Use the deflate scheme, with compression factor of

.Fl 1

.Fl 9 .

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Compressed or uncompressed output is written to the standard output.

No files are modified (force

.Nm zcat

.Nm gzcat

mode).

.It Fl d

Decompress the source files instead of compressing them (force

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is also given, copy the input data without change

to the standard output: let

.Nm zcat

.Nm gzcat

behave as

.Xr cat 1 .

.It Fl g

Use deflate scheme which reportedly provides better compression rates (force

Use the deflate scheme, which reportedly provides better compression rates

.Nm gzip

(force

.Xr gzip 1

mode).

This flag need not be specified when invoked as

.Nm gzip

.Nm gzcat .

.It Fl h

Print a short help message.

.It Fl L

Print the license.

.It Fl l

List information for the specified compressed files.

The following information is listed:

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.It Fl N

When compressing, save the original file name and time stamp in the

compressed file.

This information is saved by default when the deflate scheme is used.

This information is saved by default when the deflate scheme

.Pf ( Fl g )

is used.

When uncompressing or listing, use the time stamp and file name stored

in the compressed file, if any, for the uncompressed version.

.It Fl n

When compressing, do not save the original file name and time stamp.

This information is saved by default when the deflate scheme is used.

This information is saved by default when the deflate scheme

.Pf ( Fl g )

is used.

When uncompressing, do not restore the original file name and time stamp.

By default, the uncompressed file inherits the time stamp of the

compressed version and the uncompressed file name is generated from

the name of the compressed file name as described above.

.It Fl O

Use old compression method.

Use compress mode

(the default).

.It Fl o Ar filename

Set the output file name.

.It Fl q

Be quiet, suppress all messages.

Be quiet: suppress all messages.

.It Fl r

Recursive mode,

Recursive mode:

.Nm

will descend into specified directories.

.It Fl S Ar suffix

Set suffix for compressed files.

Set the suffix for compressed files.

.It Fl t

Test the integrity of each file leaving any files intact.

.It Fl V

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Print the percentage reduction of each file and other information.

.El

.Pp

In normal mode,

.Nm

uses a modified Lempel-Ziv algorithm

.Pq LZW .

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.Dq block

of the file.

.Pp

.Nm gzip

uses a slightly different version of the Lempel-Ziv algorithm

.Pq LZ77 .

Common substrings are replaced by pointers to previous strings,

and are found using a hash table.

Unique substrings are emitted as a string of literal bytes,

and compressed as Huffman trees.

.Pp

The

.Fl b

flag is omitted for

.Nm uncompress

.Nm gunzip

since the

.Ar bits

parameter specified during compression

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.Ar bits

per code, and the distribution of common substrings.

Typically, text such as source code or English is reduced by 50 \- 60% using

.Nm

.Nm .

and by 60 \- 70% using

.Nm gzip .

Compression is generally much better than that achieved by Huffman

coding (as used in the historical command pack), or adaptive Huffman

coding (as used in the historical command compact), and takes less

time to compute.

.Pp

The

.Nm

.Nm compress ,

.Nm uncompress ,

and

.Nm gzip

.Nm zcat

utilities exit with 0 on success; 1 if an error occurred;

or 2 if a warning occurred.

.Sh SEE ALSO

.Xr gzexe 1 ,

.Xr gzip 1 ,

.Xr zdiff 1 ,

.Xr zforce 1 ,

.Xr zmore 1 ,

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.%V 17:6

.%P pp. 8\-19

.Re

.Pp

.Bl -tag -width 12n -compact

.It RFC 1950

ZLIB Compressed Data Format Specification.

.It RFC 1951

DEFLATE Compressed Data Format Specification.

.It RFC 1952

GZIP File Format Specification.

.El

.Sh STANDARDS

The

.Nm

utility is compliant with the

.St -p1003.2-92

specification.

.Pp

The

.Nm gzip

and

.Nm gunzip

utilities are extensions.

.Sh HISTORY

The

.Nm

command appeared in

.Bx 4.3 .

The deflate compression support was added in

Deflate compression support was added in

.Ox 2.1 .

Full

.Nm gzip

compatibility was added in

.Ox 3.4 .

The

.Sq g

in this version of

.Nm gzip

stands for

.Dq gratis .