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author | nate <nate@FreeBSD.org> | 1993-06-18 18:39:41 +0000 |
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committer | nate <nate@FreeBSD.org> | 1993-06-18 18:39:41 +0000 |
commit | 12c4fd169736d45ab4b2b3f55301ecceaf9c67b3 (patch) | |
tree | ff423954f6049c9cdc9673d76e5867f99adeeb7e /gnu/usr.bin/gzip/gzip.1 | |
parent | 7067738d6ce62410bf037507ed279733f38b3910 (diff) | |
download | FreeBSD-src-12c4fd169736d45ab4b2b3f55301ecceaf9c67b3.zip FreeBSD-src-12c4fd169736d45ab4b2b3f55301ecceaf9c67b3.tar.gz |
Gzip 1.1
Diffstat (limited to 'gnu/usr.bin/gzip/gzip.1')
-rw-r--r-- | gnu/usr.bin/gzip/gzip.1 | 360 |
1 files changed, 360 insertions, 0 deletions
diff --git a/gnu/usr.bin/gzip/gzip.1 b/gnu/usr.bin/gzip/gzip.1 new file mode 100644 index 0000000..a7d331f --- /dev/null +++ b/gnu/usr.bin/gzip/gzip.1 @@ -0,0 +1,360 @@ +.PU +.TH GZIP 1 +.SH NAME +gzip, gunzip, zcat \- compress or expand files +.SH SYNOPSIS +.ll +8 +.B gzip +.RB [ " \-acdfhLrtvV19 " ] +.RB [ \-S\ suffix ] +[ +.I "name \&..." +] +.ll -8 +.br +.B gunzip +.RB [ " \-acfhLrtvV " ] +.RB [ \-S\ suffix ] +[ +.I "name \&..." +] +.br +.B zcat +.RB [ " \-hLV " ] +[ +.I "name \&..." +] +.SH DESCRIPTION +.I Gzip +reduces the size of the named files using Lempel-Ziv coding (LZ77). +Whenever possible, +each file is replaced by one with the extension +.B "\&.gz," +while keeping the same ownership modes, access and modification times. +(The default extension is +.B "\-gz" +for VMS, +.B "z" +for MSDOS, OS/2 and Atari.) +If no files are specified, the standard input is compressed to the +standard output. If the new file name is too long, +.I gzip +truncates it and keeps the original file name in the compressed file. +.I Gzip +will only attempt to compress regular files. +In particular, it will ignore symbolic links. +.PP +Compressed files can be restored to their original form using +.I gzip -d +or +.I gunzip +or +.I zcat. +.PP +.I gunzip +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. +.I gunzip +also recognizes the special extensions +.B "\&.tgz" +and +.B "\&.taz" +as shorthands for +.B "\&.tar.gz" +and +.B "\&.tar.Z" +respectively. +.PP +.I gunzip +can currently decompress files created by +.I gzip, zip, compress +or +.I pack. +The detection of the input format is automatic. When using +the first two formats, +.I gunzip +checks a 32 bit CRC. For +.I pack, gunzip +checks the uncompressed length. The +.I compress +format was not designed to allow consistency checks. However +.I gunzip +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 +.I uncompress +does not complain. This generally means that the standard +.I uncompress +does not check its input, and happily generates garbage output. +.PP +Files created by +.I zip +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 +.I unzip +instead of +.I gunzip. +.PP +.I zcat +is identical to +.I gunzip +.B \-c. +(On some systems, +.I zcat +may be installed as +.I gzcat +to preserve the original link to +.I compress.) +.I zcat +uncompresses either a list of files on the command line or its +standard input and writes the uncompressed data on standard output. +.I zcat +will uncompress files that have the correct magic number whether +they have a +.B "\&.gz" +suffix or not. +.PP +.I Gzip +uses the Lempel-Ziv algorithm used in +.I zip +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 +.IR compress ), +Huffman coding (as used in +.IR pack ), +or adaptive Huffman coding +.RI ( compact ). +.PP +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. +.I gzip +preserves the mode, ownership and timestamps of files when compressing +or decompressing. + +.SH OPTIONS +.TP +.B \-a --ascii +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. +.TP +.B \-c --stdout +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. +.TP +.B \-d --decompress --uncompress +Decompress. +.TP +.B \-f --force +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 +.B \-f +is not given, +and when not running in the background, +.I gzip +prompts to verify whether an existing file should be overwritten. +.TP +.B \-h --help +Display a help screen and quit. +.TP +.B \-L --license +Display the +.I gzip +license. +.TP +.B \-q --quiet +Suppress all warnings. +.TP +.B \-r --recurse +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 .z --suffix .z +Use suffix .z 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. 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. +.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 (optimal compression). +The default compression level is +.BR \-5. +.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: + + zcat old.gz | gzip > new.gz +.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="-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. +.SH "SEE ALSO" +znew(1), zcmp(1), zmore(1), zforce(1), gzexe(1), zip(1), unzip(1), compress(1), +pack(1), compact(1) +.SH "DIAGNOSTICS" +Exit status is normally 0; +if an error occurs, exit status is 1. If a warning occurs, exit status is 2. +.PP +Usage: gzip [-cdfhLrtvV19] [-S suffix] [file ...] +.in +8 +Invalid options were specified on the command line. +.in -8 +.IR file : +not in gzip format +.in +8 +The file specified to +.I gunzip +has not been compressed. +.in -8 +.IR file: +Corrupt input. Use zcat to recover some data. +.in +8 +The compressed file has been damaged. The data up to the point of failure +can be recovered using +.in +8 +zcat file > recover +.in -16 +.IR file : +compressed with +.I xx +bits, can only handle +.I yy +bits +.in +8 +.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. +.in -8 +.IR file : +already has .gz suffix -- no change +.in +8 +The file is assumed to be already compressed. +Rename the file and try again. +.in -8 +.I file +already exists; do you wish to overwrite (y or n)? +.in +8 +Respond "y" if you want the output file to be replaced; "n" if not. +.in -8 +gunzip: corrupt input +.in +8 +A SIGSEGV violation was detected which usually means that the input file has +been corrupted. +.in -8 +.I "xx.x%" +.in +8 +Percentage of the input saved by compression. +(Relevant only for +.BR \-v \.) +.in -8 +-- not a regular file or directory: ignored +.in +8 +When the input file is not a regular file or directory, +(e.g. a symbolic link, socket, FIFO, device file), it is +left unaltered. +.in -8 +-- has +.I xx +other links: unchanged +.in +8 +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. +.in -8 +.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 /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. |