.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 redundancy\&.
.PP 
.SH "OPTIONS SUMMARY" 
.PP 
Here is a summary of the options to rzip\&.

.nf 
 

-0, --worst            fastest (worst) compression
-6                     default compression level
-9, --best             slowest (best) compression
-d, --decompress       decompress
-f, --force            force overwrite of any existing files
-o, --output FILENAME  specify the output file name
-k, --keep             keep existing files
-L, --level LEVEL      set compression level
-P, --progress         show compression progress
-S, --suffix SUFFIX    specify compressed suffix (default \&'\&.rz\&')
-v, --verbose          increase verbosity
-V, --version          show version

.fi 
 

.PP 
.SH "OPTIONS" 
.PP 
.IP "\fB-h --help\fP" 
Print an options summary page
.IP 
.IP "\fB-V --version\fP" 
Print the rzip version number
.IP 
.IP "\fB-0 (or --worst) to -9 (or --best) --level\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 --decompress\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 --output\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 --suffix\fP" 
Set the compression suffix\&. The default is \&'\&.rz\&'\&.
.IP 
.IP "\fB-f --force\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 --keep\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 --progress\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\&.