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LZ4(1) User Commands LZ4(1)
NAME
lz4 - lz4, unlz4, lz4cat - Compress or decompress .lz4 files
SYNOPSIS
lz4 [OPTIONS] [-|INPUT-FILE] OUTPUT-FILE
unlz4 is equivalent to lz4 -d
lz4cat is equivalent to lz4 -dcfm
When writing scripts that need to decompress files, it is recommended to always use the
name lz4 with appropriate arguments (lz4 -d or lz4 -dc) instead of the names unlz4 and
lz4cat.
DESCRIPTION
lz4 is an extremely fast lossless compression algorithm, based on byte-aligned LZ77 family
of compression scheme. lz4 offers compression speeds of 400 MB/s per core, linearly scal-
able with multi-core CPUs. It features an extremely fast decoder, with speed in multiple
GB/s per core, typically reaching RAM speed limit on multi-core systems. The native file
format is the .lz4 format.
Difference between lz4 and gzip
lz4 supports a command line syntax similar but not identical to gzip(1). Differences are :
o lz4 preserves original files
o lz4 compresses a single file by default (see -m for multiple files)
o lz4 file1 file2 means : compress file1 into file2
o lz4 file.lz4 will default to decompression (use -z to force compression)
o lz4 shows real-time notification statistics during compression or decompression of a
single file (use -q to silence them)
o If no destination name is provided, result is sent to stdout except if stdout is the
console.
o If no destination name is provided, and if stdout is the console, file is compressed
into file.lz4.
o As a consequence of previous rules, note the following example : lz4 file | consumer
sends compressed data to consumer through stdout, hence it does not create file.lz4.
o Another consequence of those rules is that to run lz4 under nohup, you should provide
a destination file: nohup lz4 file file.lz4, because nohup writes the specified com-
mand's output to a file.
Default behaviors can be modified by opt-in commands, detailed below.
o lz4 -m makes it possible to provide multiple input filenames, which will be compressed
into files using suffix .lz4. Progress notifications are also disabled by default (use
-v to enable them). This mode has a behavior which more closely mimics gzip command
line, with the main remaining difference being that source files are preserved by
default.
o Similarly, lz4 -m -d can decompress multiple *.lz4 files.
o It's possible to opt-in to erase source files on successful compression or decompres-
sion, using --rm command.
o Consequently, lz4 -m --rm behaves the same as gzip.
Concatenation of .lz4 files
It is possible to concatenate .lz4 files as is. lz4 will decompress such files as if they
were a single .lz4 file. For example:
lz4 file1 > foo.lz4
lz4 file2 >> foo.lz4
Then lz4cat foo.lz4 is equivalent to cat file1 file2.
OPTIONS
Short commands concatenation
In some cases, some options can be expressed using short command -x or long command
--long-word. Short commands can be concatenated together. For example, -d -c is equivalent
to -dc. Long commands cannot be concatenated. They must be clearly separated by a space.
Multiple commands
When multiple contradictory commands are issued on a same command line, only the latest
one will be applied.
Operation mode
-z --compress
Compress. This is the default operation mode when no operation mode option is spec-
ified, no other operation mode is implied from the command name (for example, unlz4
implies --decompress), nor from the input file name (for example, a file extension
.lz4 implies --decompress by default). -z can also be used to force compression of
an already compressed .lz4 file.
-d --decompress --uncompress
Decompress. --decompress is also the default operation when the input filename has
an .lz4 extension.
-t --test
Test the integrity of compressed .lz4 files. The decompressed data is discarded. No
files are created nor removed.
-b# Benchmark mode, using # compression level.
Operation modifiers
-# Compression level, with # being any value from 1 to 12. Higher values trade com-
pression speed for compression ratio. Values above 12 are considered the same as
12. Recommended values are 1 for fast compression (default), and 9 for high com-
pression. Speed/compression trade-off will vary depending on data to compress.
Decompression speed remains fast at all settings.
-D dictionaryName
Compress, decompress or benchmark using dictionary dictionaryName. Compression and
decompression must use the same dictionary to be compatible. Using a different dic-
tionary during decompression will either abort due to decompression error, or gen-
erate a checksum error.
-f --[no-]force
This option has several effects:
If the target file already exists, overwrite it without prompting.
When used with --decompress and lz4 cannot recognize the type of the source file,
copy the source file as is to standard output. This allows lz4cat --force to be
used like cat (1) for files that have not been compressed with lz4.
-c --stdout --to-stdout
Force write to standard output, even if it is the console.
-m --multiple
Multiple input files. Compressed file names will be appended a .lz4 suffix. This
mode also reduces notification level. lz4 -m has a behavior equivalent to gzip -k
(it preserves source files by default).
-r operate recursively on directories. This mode also sets -m (multiple input files).
-B# Block size [4-7](default : 7)
-B4= 64KB ; -B5= 256KB ; -B6= 1MB ; -B7= 4MB
-BD Block Dependency (improves compression ratio on small blocks)
--fast[=#]
switch to ultra-fast compression levels. If =# is not present, it defaults to 1.
The higher the value, the faster the compression speed, at the cost of some com-
pression ratio. This setting overwrites compression level if one was set previ-
ously. Similarly, if a compression level is set after --fast, it overrides it.
--[no-]frame-crc
Select frame checksum (default:enabled)
--[no-]content-size
Header includes original size (default:not present)
Note : this option can only be activated when the original size can be determined,
hence for a file. It won't work with unknown source size, such as stdin or pipe.
--[no-]sparse
Sparse mode support (default:enabled on file, disabled on stdout)
-l Use Legacy format (typically for Linux Kernel compression)
Note : -l is not compatible with -m (--multiple) nor -r
Other options
-v --verbose
Verbose mode
-q --quiet
Suppress warnings and real-time statistics; specify twice to suppress errors too
-h -H --help
Display help/long help and exit
-V --version
Display Version number and exit
-k --keep
Preserve source files (default behavior)
--rm Delete source files on successful compression or decompression
-- Treat all subsequent arguments as files
Benchmark mode
-b# Benchmark file(s), using # compression level
-e# Benchmark multiple compression levels, from b# to e# (included)
-i# Minimum evaluation time in seconds [1-9] (default : 3)
BUGS
Report bugs at: https://github.com/lz4/lz4/issues
AUTHOR
Yann Collet
lz4 1.8.3 September 2018 LZ4(1)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
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