File: rzip.1

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rzip 2.1-1
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.TH "rzip" "1" "October 2003" "" "" 
.SH "NAME" 
rzip \- a large-file compression program
.SH "SYNOPSIS" 
.PP 
rzip [OPTIONS] <files\&.\&.\&.>
.PP 
.SH "DESCRIPTION" 
.PP 
rzip is a file compression program designed to do particularly
well on very large files containing long distance redundency\&.
.PP 
.SH "OPTIONS SUMMARY" 
.PP 
Here is a summary of the options to rzip\&.

.nf 
 

 -0            fastest (worst) compression
 -6            default compression
 -9            slowest (best) compression
 -d            decompress
 -o filename   specify the output file name
 -S suffix     specify compressed suffix (default \&'\&.rz\&')
 -f            force overwrite of any existing files
 -k            keep existing files
 -P            show compression progress
 -V            show version

.fi 
 

.PP 
.SH "OPTIONS" 
.PP 
.IP "\fB-h\fP" 
Print an options summary page
.IP 
.IP "\fB-V\fP" 
Print the rzip version number
.IP 
.IP "\fB-0\&.\&.9\fP" 
Set the compression level from 0 to 9\&. The default is
to use level 6, which is a reasonable compromise between speed and
compression\&. The compression level is also strongly related to how much
memory rzip uses, so if you are running rzip on a machine with limited
amounts of memory then you will probably want to choose a smaller level\&.
.IP 
.IP "\fB-d\fP" 
Decompress\&. If this option is not used then rzip looks at
the name used to launch the program\&. If it contains the string
\&'runzip\&' then the -d option is automatically set\&.
.IP 
.IP "\fB-o\fP" 
Set the output file name\&. If this option is not set then
the output file name is chosen based on the input name and the
suffix\&. The -o option cannot be used if more than one file name is
specified on the command line\&.
.IP 
.IP "\fB-S\fP" 
Set the compression suffix\&. The default is \&'\&.rz\&'\&. 
.IP 
.IP "\fB-f\fP" 
If this option is not specified then rzip will not
overwrite any existing files\&. If you set this option then rzip will
silently overwrite any files as needed\&.
.IP 
.IP "\fB-k\fP" 
If this option is not specified then rzip will delete the
source file after successful compression or decompression\&. When this
option is specified then the source files are not deleted\&.
.IP 
.IP "\fB-P\fP" 
If this option is specified then rzip will show the
percentage progress while compressing\&.
.IP 
.PP 
.SH "INSTALLATION" 
.PP 
Just install rzip in your search path\&.
.PP 
.SH "COMPRESSION ALGORITHM" 
.PP 
rzip operates in two stages\&. The first stage finds and encodes large
chunks of duplicated data over potentially very long distances (up to
nearly a gigabyte) in the input file\&. The second stage is to use a
standard compression algorithm (bzip2) to compress the output of the
first stage\&.
.PP 
The key difference between rzip and other well known compression
algorithms is its ability to take advantage of very long distance
redundency\&. The well known deflate algorithm used in gzip uses a
maximum history buffer of 32k\&. The block sorting algorithm used in
bzip2 is limited to 900k of history\&. The history buffer in rzip can be
up to 900MB long, several orders of magnitude larger than gzip or
bzip2\&.
.PP 
It is quite common these days to need to compress files that contain
long distance redundancies\&. For example, when compressing a set of
home directories several users might have copies of the same file, or
of quite similar files\&. It is also common to have a single file that
contains large duplicated chunks over long distances, such as pdf
files containing repeated copies of the same image\&. Most compression
programs won\&'t be able to take advantage of this redundency, and thus
might achieve a much lower compression ratio than rzip can achieve\&.
.PP 
.SH "HISTORY" 
.PP 
The ideas behind rzip were first implemented in 1998 while I was
working on rsync\&. That version was too slow to be practical, and was
replaced by this version in 2003\&.
.PP 
.SH "BUGS" 
.PP 
Unlike most Unix compression programs, rzip cannot compress or
decompress to or from standard input or standard output\&. This is due
to the nature of the algorithm that rzip uses and cannot easily be
fixed\&. 
.PP 
.SH "CREDITS" 
.PP 
Thanks to the following people for their contributions to rzip
.IP o 
Paul Russell for many suggestions and the debian packaging
.IP o 
The authors of bzlib for an excellent library
.PP 
.SH "AUTHOR" 
.PP 
rzip was written by Andrew Tridgell
http://samba\&.org/~tridge/
.PP 
If you wish to report a problem or make a suggestion then please email
bugs-rzip@tridgell\&.net
.PP 
rzip is released under the GNU General Public License version 2 or
later\&. Please see the file COPYING for license details\&.