+GZIP(1) General Commands Manual GZIP(1)
+
+1mNAME0m
+ gzip, gunzip, zcat - compress or expand files
+
+1mSYNOPSIS0m
+ 1mgzip 22m[ 1m-acdfhklLnNrtvV19 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
+ 1mgunzip 22m[ 1m-acfhklLnNrtvV 22m] [1m-S suffix22m] [ 4mname24m 4m...24m ]
+ 1mzcat 22m[ 1m-fhLV 22m] [ 4mname24m 4m...24m ]
+
+1mDESCRIPTION0m
+ 4mGzip24m reduces the size of the named files using Lempel-Ziv coding
+ (LZ77). Whenever possible, each file is replaced by one with the
+ extension 1m.gz22m, while keeping the same ownership modes, access and modi-
+ fication times. (The default extension is 1m-gz 22mfor VMS, 1mz 22mfor 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. 4mGzip24m will only attempt to compress regular files. In particu-
+ lar, it will ignore symbolic links.
+
+ If the compressed file name is too long for its file system, 4mgzip24m trun-
+ cates it. 4mGzip24m 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, 4mgzip24m keeps the original file name and timestamp in the com-
+ pressed file. These are used when decompressing the file with the 1m-N0m
+ 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 4mgzip24m 4m-d0m
+ or 4mgunzip24m or 4mzcat24m. 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.
+
+ 4mgunzip24m takes a list of files on its command line and replaces each file
+ whose name ends with .gz, -gz, .z, -z, or _z (ignoring case) and which
+ begins with the correct magic number with an uncompressed file without
+ the original extension. 4mgunzip24m also recognizes the special extensions
+ 1m.tgz 22mand 1m.taz 22mas shorthands for 1m.tar.gz 22mand 1m.tar.Z 22mrespectively. When
+ compressing, 4mgzip24m uses the 1m.tgz 22mextension if necessary instead of trun-
+ cating a file with a 1m.tar 22mextension.
+
+ 4mgunzip24m can currently decompress files created by 4mgzip24m, 4mzip24m, 4mcompress24m,
+ 4mcompress24m 4m-H24m or 4mpack24m. The detection of the input format is automatic.
+ When using the first two formats, 4mgunzip24m checks a 32 bit CRC. For 4mpack0m
+ and 4mgunzip24m checks the uncompressed length. The standard 4mcompress24m format
+ was not designed to allow consistency checks. However 4mgunzip24m is some-
+ times able to detect a bad .Z file. If you get an error when uncom-
+ pressing a .Z file, do not assume that the .Z file is correct simply
+ because the standard 4muncompress24m does not complain. This generally means
+ that the standard 4muncompress24m does not check its input, and happily gen-
+ erates garbage output. The SCO compress -H format (lzh compression
+ method) does not include a CRC but also allows some consistency checks.
+
+ Files created by 4mzip24m 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 a 4mzip24m file with a single member, use a command like 4mgunzip0m
+ 4m<foo.zip24m or 4mgunzip24m 4m-S24m 4m.zip24m 4mfoo.zip24m. To extract zip files with several
+ members, use 4munzip24m instead of 4mgunzip24m.
+
+ 4mzcat24m is identical to 4mgunzip24m 1m-c22m. (On some systems, 4mzcat24m may be
+ installed as 4mgzcat24m to preserve the original link to 4mcompress24m.) 4mzcat0m
+ uncompresses either a list of files on the command line or its standard
+ input and writes the uncompressed data on standard output. 4mzcat24m will
+ uncompress files that have the correct magic number whether they have a
+ 1m.gz 22msuffix or not.
+
+ 4mGzip24m uses the Lempel-Ziv algorithm used in 4mzip24m and PKZIP. The amount
+ of compression obtained depends on the size of the input and the dis-
+ tribution 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 4mcompress24m), Huffman coding (as
+ used in 4mpack24m), or adaptive Huffman coding (4mcompact24m).
+
+ 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. 4mgzip24m preserves the mode,
+ ownership and timestamps of files when compressing or decompressing.
+
+1mOPTIONS0m
+ 1m-a --ascii0m
+ 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 con-
+ verted to CR LF when decompressing.
+
+ 1m-c --stdout --to-stdout0m
+ 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.
+
+ 1m-d --decompress --uncompress0m
+ Decompress.
+
+ 1m-f --force0m
+ Force compression or decompression even if the file has multiple
+ links or the corresponding file already exists, or if the com-
+ pressed data is read from or written to a terminal. If the input
+ data is not in a format recognized by 4mgzip24m, and if the option
+ --stdout is also given, copy the input data without change to
+ the standard output: let 4mzcat24m behave as 4mcat24m. If 1m-f 22mis not
+ given, and when not running in the background, 4mgzip24m prompts to
+ verify whether an existing file should be overwritten.
+
+ 1m-h --help0m
+ Display a help screen and quit.
+
+ 1m-k --keep0m
+ Keep (don't delete) input files during compression or decompres-
+ sion.
+
+ 1m-l --list0m
+ 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 for-
+ mat, such as compressed .Z files. To get the uncompressed size
+ for such a file, you can use:
+
+ zcat 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, com-
+ press, 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.
+
+ 1m-L --license0m
+ Display the 4mgzip24m license and quit.
+
+ 1m-n --no-name0m
+ 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 4mgzip24m 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.
+
+ 1m-N --name0m
+ 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.
+
+ 1m-q --quiet0m
+ Suppress all warnings.
+
+ 1m-r --recursive0m
+ Travel the directory structure recursively. If any of the file
+ names specified on the command line are directories, 4mgzip24m will
+ descend into the directory and compress all the files it finds
+ there (or decompress them in the case of 4mgunzip24m ).
+
+ 1m-S .suf --suffix .suf0m
+ When compressing, use suffix .suf instead of .gz. Any non-empty
+ suffix can be given, but suffixes other than .z and .gz should
+ be avoided to avoid confusion when files are transferred to
+ other systems.
+
+ When decompressing, add .suf to the beginning of the list of
+ suffixes to try, when deriving an output file name from an input
+ file name.
+
+ 1m--synchronous0m
+ Use synchronous output. With this option, 4mgzip24m is less likely
+ to lose data during a system crash, but it can be considerably
+ slower.
+
+ 1m-t --test0m
+ Test. Check the compressed file integrity.
+
+ 1m-v --verbose0m
+ Verbose. Display the name and percentage reduction for each file
+ compressed or decompressed.
+
+ 1m-V --version0m
+ Version. Display the version number and compilation options then
+ quit.
+
+ 1m-# --fast --best0m
+ Regulate the speed of compression using the specified digit 4m#24m,
+ where 1m-1 22mor 1m--fast 22mindicates the fastest compression method
+ (less compression) and 1m-9 22mor 1m--best 22mindicates the slowest com-
+ pression method (best compression). The default compression
+ level is 1m-6 22m(that is, biased towards high compression at expense
+ of speed).