lunzip/README

See the file INSTALL for compilation and installation instructions.

Description

Lunzip is a decompressor for the lzip format written in C. Its small size
makes it well suited for embedded devices or software installers that need
to decompress files but don't need compression capabilities.

Lzip is a lossless data compressor with a user interface similar to the one
of gzip or bzip2. Lzip uses a simplified form of LZMA (Lempel-Ziv-Markov
chain-Algorithm) designed to achieve complete interoperability between
implementations. The maximum dictionary size is 512 MiB so that any lzip
file can be decompressed on 32-bit machines. Lzip provides accurate and
robust 3-factor integrity checking. 'lzip -0' compresses about as fast as
gzip, while 'lzip -9' compresses most files more than bzip2. Decompression
speed is intermediate between gzip and bzip2. Lzip provides better data
recovery capabilities than gzip and bzip2. Lzip has been designed, written,
and tested with great care to replace gzip and bzip2 as general-purpose
compressed format for Unix-like systems.

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

   * The program lziprecover 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 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 option '--buffer-size' and lunzip will use the decompressed
file as dictionary for distances beyond the buffer size. Of course, the
larger the difference between the buffer size and the dictionary size, the
more accesses to disc 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 option '--buffer-size' may help to decompress a file erroneously created
with a dictionary size much larger than the uncompressed size. (Lzip adjusts
the dictionary size to the uncompressed size, but third-party tools may not).

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
'--buffer-size' is specified.

When decompressing, 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, if you have
appropriate privileges, 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 either the
option '-c' or the option '-o' is specified.

If no file names are specified, lunzip decompresses from standard input to
standard output. In this case, lunzip refuses to read compressed input from
a terminal, as this might leave the terminal in an abnormal state.

Lunzip correctly decompresses a file which is the concatenation of two or
more compressed files. The result is the concatenation of the corresponding
decompressed 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), Andrei 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).

LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never have
been compressed. Decompressed is used to refer to data which have undergone
the process of decompression.

Lunzip uses Arg_parser for command-line argument parsing:
http://www.nongnu.org/arg-parser/arg_parser.html


Copyright (C) 2010-2025 Antonio Diaz Diaz.

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

The file Makefile.in is a data file used by configure to produce the Makefile.
It has the same copyright owner and permissions that configure itself.