Description

Lunzip is a decompressor for the lzip format. It is written in C and its
small size makes it well suited for embedded devices or software
installers that need to decompress files but don't need compression
capabilities. Lunzip is fully compatible with lzip-1.4 or newer.

The lzip file format is designed for data sharing and long-term
archiving, taking into account both data integrity and decoder
availability:

   * The lzip format provides very safe integrity checking and some data
     recovery means. The lziprecover program can repair bit-flip errors
     (one of the most common forms of data corruption) in lzip files,
     and provides data recovery capabilities, including error-checked
     merging of damaged copies of a file.

   * The lzip format is as simple as possible (but not simpler). The
     lzip manual provides the source code of a simple decompressor along
     with a detailed explanation of how it works, so that with the only
     help of the lzip manual it would be possible for a digital
     archaeologist to extract the data from a lzip file long after
     quantum computers eventually render LZMA obsolete.

   * Additionally the lzip reference implementation is copylefted, which
     guarantees that it will remain free forever.

A nice feature of the lzip format is that a corrupt byte is easier to
repair the nearer it is from the beginning of the file. Therefore, with
the help of lziprecover, losing an entire archive just because of a
corrupt byte near the beginning is a thing of the past.

Lunzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer than decompressors returning ambiguous
warning values (like gunzip) when it is used as a back end for other
programs like tar or zutils.

Lunzip provides a "low memory" mode able to decompress any file using as
little memory as 50 kB, irrespective of the dictionary size used to
compress the file. To activate it, specify the size of the output buffer
with the "--buffer-size" option and lunzip will use the decompressed
file as dictionary for distances beyond the buffer size. Of course, the
smaller the buffer size used in relation to the dictionary size, the
more accesses to disk are needed and the slower the decompression is.
This "low memory" mode only works when decompressing to a regular file
and is intended for systems without enough memory (RAM + swap) to keep
the whole dictionary at once. It has been tested on a laptop with a 486
processor and 4 MiB of RAM.

The amount of memory required by lunzip to decompress a file is about
46 kB larger than the dictionary size used to compress that file, unless
the "--buffer-size" option is specified.

Lunzip attempts to guess the name for the decompressed file from that of
the compressed file as follows:

filename.lz    becomes   filename
filename.tlz   becomes   filename.tar
anyothername   becomes   anyothername.out

Decompressing a file is much like copying or moving it; therefore lunzip
preserves the access and modification dates, permissions, and, when
possible, ownership of the file just as "cp -p" does. (If the user ID or
the group ID can't be duplicated, the file permission bits S_ISUID and
S_ISGID are cleared).

Lunzip is able to read from some types of non regular files if the
"--stdout" option is specified.

If no file names are specified, lunzip decompresses from standard input
to standard output. In this case, lunzip will decline to read compressed
input from a terminal.

Lunzip will correctly decompress a file which is the concatenation of
two or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.

The ideas embodied in lunzip are due to (at least) the following people:
Abraham Lempel and Jacob Ziv (for the LZ algorithm), Andrey Markov (for
the definition of Markov chains), G.N.N. Martin (for the definition of
range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI).


Copyright (C) 2010-2017 Antonio Diaz Diaz.

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

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