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diff --git a/Build/source/utils/gzip/gzip_2.html b/Build/source/utils/gzip/gzip_2.html new file mode 100644 index 00000000000..197bc4ffc7f --- /dev/null +++ b/Build/source/utils/gzip/gzip_2.html @@ -0,0 +1,119 @@ +<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> |