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+<HTML>
+<HEAD>
+<!-- Created by texi2html 1.56k from gzip.texi on 9 August 2001 -->
+
+<TITLE>Gzip User's Manual - 1. Overview</TITLE>
+</HEAD>
+<BODY>
+Go to the <A HREF="gzip_1.html">first</A>, <A HREF="gzip_1.html">previous</A>, <A HREF="gzip_3.html">next</A>, <A HREF="gzip_9.html">last</A> section, <A HREF="gzip_toc.html">table of contents</A>.
+<P><HR><P>
+
+
+<H1><A NAME="SEC4" HREF="gzip_toc.html#TOC4">1. Overview</A></H1>
+<P>
+<A NAME="IDX1"></A>
+
+
+<P>
+<CODE>gzip</CODE> reduces the size of the named files using Lempel-Ziv coding
+(LZ77). Whenever possible, each file is replaced by one with the
+extension <SAMP>`.gz'</SAMP>, while keeping the same ownership modes, access and
+modification times. (The default extension is <SAMP>`-gz'</SAMP> for VMS,
+<SAMP>`z'</SAMP> for MSDOS, OS/2 FAT and Atari.) If no files are specified or
+if a file name is "-", the standard input is compressed to the standard
+output. <CODE>gzip</CODE> will only attempt to compress regular files. In
+particular, it will ignore symbolic links.
+
+
+<P>
+If the new file name is too long for its file system, <CODE>gzip</CODE>
+truncates it. <CODE>gzip</CODE> 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.
+
+
+<P>
+By default, <CODE>gzip</CODE> keeps the original file name and timestamp in
+the compressed file. These are used when decompressing the file with the
+<SAMP>`-N'</SAMP> option. This is useful when the compressed file name was
+truncated or when the time stamp was not preserved after a file
+transfer.
+
+
+<P>
+Compressed files can be restored to their original form using <SAMP>`gzip -d'</SAMP>
+or <CODE>gunzip</CODE> or <CODE>zcat</CODE>. 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.
+
+
+<P>
+<CODE>gunzip</CODE> takes a list of files on its command line and replaces
+each file whose name ends with <SAMP>`.gz'</SAMP>, <SAMP>`.z'</SAMP>, <SAMP>`.Z'</SAMP>,
+<SAMP>`-gz'</SAMP>, <SAMP>`-z'</SAMP> or <SAMP>`_z'</SAMP> and which begins with the correct
+magic number with an uncompressed file without the original extension.
+<CODE>gunzip</CODE> also recognizes the special extensions <SAMP>`.tgz'</SAMP> and
+<SAMP>`.taz'</SAMP> as shorthands for <SAMP>`.tar.gz'</SAMP> and <SAMP>`.tar.Z'</SAMP>
+respectively. When compressing, <CODE>gzip</CODE> uses the <SAMP>`.tgz'</SAMP>
+extension if necessary instead of truncating a file with a <SAMP>`.tar'</SAMP>
+extension.
+
+
+<P>
+<CODE>gunzip</CODE> can currently decompress files created by <CODE>gzip</CODE>,
+<CODE>zip</CODE>, <CODE>compress</CODE> or <CODE>pack</CODE>. The detection of the input
+format is automatic. When using the first two formats, <CODE>gunzip</CODE>
+checks a 32 bit CRC (cyclic redundancy check). For <CODE>pack</CODE>,
+<CODE>gunzip</CODE> checks the uncompressed length. The <CODE>compress</CODE> format
+was not designed to allow consistency checks. However <CODE>gunzip</CODE> is
+sometimes able to detect a bad <SAMP>`.Z'</SAMP> file. If you get an error when
+uncompressing a <SAMP>`.Z'</SAMP> file, do not assume that the <SAMP>`.Z'</SAMP> file is
+correct simply because the standard <CODE>uncompress</CODE> does not complain.
+This generally means that the standard <CODE>uncompress</CODE> does not check
+its input, and happily generates garbage output. The SCO <SAMP>`compress
+-H'</SAMP> format (<CODE>lzh</CODE> compression method) does not include a CRC but
+also allows some consistency checks.
+
+
+<P>
+Files created by <CODE>zip</CODE> can be uncompressed by <CODE>gzip</CODE> only if
+they have a single member compressed with the 'deflation' method. This
+feature is only intended to help conversion of <CODE>tar.zip</CODE> files to
+the <CODE>tar.gz</CODE> format. To extract <CODE>zip</CODE> files with several
+members, use <CODE>unzip</CODE> instead of <CODE>gunzip</CODE>.
+
+
+<P>
+<CODE>zcat</CODE> is identical to <SAMP>`gunzip -c'</SAMP>. <CODE>zcat</CODE>
+uncompresses either a list of files on the command line or its standard
+input and writes the uncompressed data on standard output. <CODE>zcat</CODE>
+will uncompress files that have the correct magic number whether they
+have a <SAMP>`.gz'</SAMP> suffix or not.
+
+
+<P>
+<CODE>gzip</CODE> uses the Lempel-Ziv algorithm used in <CODE>zip</CODE> 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 <CODE>compress</CODE>), Huffman
+coding (as used in <CODE>pack</CODE>), or adaptive Huffman coding
+(<CODE>compact</CODE>).
+
+
+<P>
+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 <CODE>gzip</CODE> 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. <CODE>gzip</CODE> preserves the mode,
+ownership and timestamps of files when compressing or decompressing.
+
+
+<P><HR><P>
+Go to the <A HREF="gzip_1.html">first</A>, <A HREF="gzip_1.html">previous</A>, <A HREF="gzip_3.html">next</A>, <A HREF="gzip_9.html">last</A> section, <A HREF="gzip_toc.html">table of contents</A>.
+</BODY>
+</HTML>