uncompress(1)                                             uncompress(1)

  gzip

  NAME

    gzip, gunzip, uncompress, zcat - compress or expand files

  SYNOPSIS

    gzip [ -cdfhlLnNqrtvV19 ] [-S suffix ] [name ...]

    gunzip [ -cdfhlLnNqrtvV19] [ -S suffix ] [ name ... ]

    uncompress [-cCdf?hkKvV] [-b maxbits] [-Iinpath] [-Ooutpath]
    [filenames...]

    zcat [-cCdf?hkKvV][-b maxbits][-Iinpath][-Ooutpath][filenames...]

  DESCRIPTION

    The gzip(1) utility reduces the size of the named files using Lempel-Ziv
    coding (LZ77). Whenever possible, each file is replaced by one with the
    extension .gz, while keeping the same ownership modes, access, and
    modification times. If no files are specified, or if a file name is "-",
    the standard input is compressed to the standard output. The gzip(1)
    utility will attempt to compress regular files only. In particular, it
    will ignore symbolic links.

    If the compressed file name is too long for its file system, gzip
    truncates it. The gzip(1) utility attempts to truncate only the parts of
    the file name longer than three 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 that do
    not have a limit on file-name length.

    By default, gzip keeps the original file name and time stamp in the
    compressed file. These are used when decompressing the file with the -
    N 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 gzip -
    d gunzip(1), uncompress(1), or zcat(1). 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.

    The gunzip(1) utility takes a list of files on its command line and
    replaces with an uncompressed file without the original extension each
    file whose name ends with .gz or .Z and begins with the correct magic
    number. The gunzip(1) utility also recognizes the special extensions .tgz
    and .taz as abbreviations for .tar.gz and .tar.Z, respectively. When
    compressing, gzip(1) uses the .tgz extension if necessary instead of
    truncating a file with a .tar extension.

    The gunzip(1) utility can currently decompress files created by gzip(1),
    zip(1), compress(1), compress -H(1) or pack(1). The detection of the input
    format is automatic. When using the first two formats, gunzip(1) performs
    a 32-bit cyclical redundancy check (CRC). For pack(1), gunzip(1) checks
    the uncompressed length. The standard compress(1) format was not designed
    to allow consistency checks. However, gunzip(1) 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
    uncompress(1) does not indicate a problem. This generally means that the
    standard uncompress(1) does not check its input and generates unreliable
    output. The Santa Cruz Operation (SCO) compress -H format (lzh compression
    method) does not include a CRC, but does allow some consistency checks.

    Files created by zip(1) can be uncompressed by gzip(1) 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 unzip(1) instead of gunzip(1).
    The uncompress(1) utility is identical to gunzip(1) except that zcat(1) is
    identical to gunzip(1) -c. (On some systems, zcat(1) can be installed as
    gzcat(1) to preserve the original link to compress)(1). The zcat(1)
    utility uncompresses either a list of files on the command line or its
    standard input and writes the uncompressed data on standard output. The
    zcat(1) utility uncompresses files that have the correct magic number,
    whether they have a .gz suffix or not.

    The gzip(1) utility uses the Lempel-Ziv algorithm used in zip(1) 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 compress(1)), Huffman coding (as
    used in pack(1)), or adaptive Huffman coding (compact(1)).

    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(1) file header, plus five 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. The gzip(1) utility preserves the mode,
    ownership, and time stamps of files when compressing or decompressing.

  OPTIONS

    The gzip(1) utility takes the following options. (The long form of the
    option letter is listed in parentheses; the long forms are preceded by two
    dashes (--).)

    -L (--license)
        Display the gzip(1) license and quit.

    -n (--no-name)
        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 gzip(1) 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.

    -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 that
        have a limit on file-name length or when the time stamp has been lost
        after a file transfer.

    -q (--quiet)
        Suppress all warnings.

    -r (--recursive)
        Travel the directory structure recursively. If any of the file names
        specified on the command line are directories, gzip(1) will descend
        into the directory and compress all the files it finds there (or
        decompress them in the case of gunzip(1)).
    -S .suf (--suffix.suf)
        Use suffix .suf instead of .gz. Any suffix can be given, but avoid
        using suffixes other than .z and .gz to prevent confusion when files
        are transferred to other systems. A null suffix forces gunzip(1) to
        try decompression on all given files regardless of suffix, as in:
        gunzip -S "" *
        Previous versions of gzip used the .z suffix. This was changed to
        avoid a conflict with pack(1).

    -t (--test)
        Test. Check the compressed file integrity.

    -v (--verbose)
        Verbose. Display the name and percentage reduction for each file
        compressed or decompressed.

    -V (--version)
        Version. Display the version number and compilation options, then
        quit.

    -# (--fast --best)
        Regulate the speed of compression using the specified digit #, where -
        1 or --fast indicates the fastest compression method (less
        compression) and -9 or --best indicates the slowest compression method
        (best compression). The default compression level is -6 (that is,
        biased towards high compression at the expense of speed).

    The uncompress(1) and zcat(1) commands use the following options:

    -V
        print Version

    -d
        do_decomp default = on

    -v
        verbose

    -f
        force overwrite of output file default = off

    -n
        no header: useful to uncompress old files

    -c
        cat all output to stdout default = off

    -C
        generate output compatible with compress 2.0.

    -k
        keep input file, default == kill (erase)

    -K
        keep output file on error, default == kill (erase)
    -b maxbits
        default == 16 bits, max == 16 bits
    -I pathname
        infile path ==
    -O pathname
        outfile path ==
    -? | -h
        help usage.

  ADVANCED USAGE

    Multiple compressed files can be concatenated. In this case, gunzip(1)
    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). You can get better
    compression by compressing all members at once, however. For example:

    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,
    use the following:

    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

    To create a single archive file with multiple members so that members can
    later be extracted independently, use an archiver, such as tar(1) or
    zip(1). GNU tar(1) supports the -z option to invoke gzip(1) transparently.
    The gzip(1) utility is designed as a complement to tar(1), not as a
    replacement.

  ENVIRONMENT VARIABLES

    The environment variable GZIP can hold a set of default options for
    gzip(1). These options are interpreted first, and can be overwritten by
    explicit command-line parameters, as shown in the following example:
    for sh:      GZIP="-8v --name"; export GZIP

    for csh:     setenv GZIP "-8v --name"

  DIAGNOSTICS

    Exit status is normally 0; if an error occurs, exit status is 1. If a
    warning occurs, exit status is 2.

    Usage: gzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
        Invalid options were specified on the command line.
    file: not in gzip format
        The file specified to gunzip(1) has not been compressed.
    file: 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 the following:
        zcat file > recover
    file: compressed with xx bits, can only handle yy bits
        The file was compressed (using LZW) by a program that could handle
        more bits than the decompress code on this computer. Recompress the
        file with gzip, which compresses better and uses less memory.
    file: already has .gz suffix -- no change
        The file is assumed to be already compressed. Rename the file and try
        again.
    file already exists; do you want to overwrite (y or n)?
        Respond "y" if you want the output file to be replaced; "n" if not.

    gunzip: corrupt input
        A SIGSEGV violation was detected, which usually means that the input
        file has been corrupted.
    xx.x%
        Percentage of the input saved by compression. (Relevant only for -
        v and -l.)

    -- not a regular file or directory: ignored
        When the input file is not a regular file or directory, (for example,
        a symbolic link, socket, first-in/first-out [FIFO], or device file),
        it is left unaltered.
    -- has xx other links: unchanged
        The input file has links; it is left unchanged. See ln(1) for more
        information. Use the -f flag to force compression of multiply linked
        files.

  CAVEATS

    When writing compressed data to a tape, it is usually necessary to pad the
    output with zeroes up to a block boundary. When the data is read and the
    whole block is passed to gunzip(1) for decompression, gunzip(1) 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 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(1) is invoked implicitly by the -z option of
    GNU tar(1). Ensure that the same block size (the -b option of tar(1)) is
    used for reading and writing compressed data on tapes. (This example
    assumes you are using the GNU version of tar(1).)

  BUGS

    The --list option reports incorrect sizes if they exceed two gigabytes.
    The --list option reports sizes as -1 and CRC as ffffffff if the
    compressed file is on a non-seekable medium.

    In rare cases, the --best option gives worse compression than the default
    compression level(-6). On some highly redundant files, traditional
    compress(1) compresses better than gzip(1); this is not true, hhowever on
    Interix, where compress(1) is a link to gzip(1).

  SEE ALSO

    zip(1)

    unzip(1)