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lz4(1) -- 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 scalable 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 :
* `lz4` compresses a single file by default (see `-m` for multiple files)
* `lz4 file1 file2` means : compress file1 _into_ file2
* `lz4 file.lz4` will default to decompression (use `-z` to force compression)
* `lz4` preserves original files
* `lz4` shows real-time notification statistics
during compression or decompression of a single file
(use `-q` to silence them)
* When no destination is specified, result is sent on implicit output,
which depends on `stdout` status.
When `stdout` _is Not the console_, it becomes the implicit output.
Otherwise, if `stdout` is the console, the implicit output is `filename.lz4`.
* It is considered bad practice to rely on implicit output in scripts.
because the script's environment may change.
Always use explicit output in scripts.
`-c` ensures that output will be `stdout`.
Conversely, providing a destination name, or using `-m`
ensures that the output will be either the specified name, or `filename.lz4` respectively.
Default behaviors can be modified by opt-in commands, detailed below.
* `lz4 -m` makes it possible to provide multiple input filenames,
which will be compressed into files using suffix `.lz4`.
Progress notifications become 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.
* Similarly, `lz4 -m -d` can decompress multiple `*.lz4` files.
* It's possible to opt-in to erase source files
on successful compression or decompression, using `--rm` command.
* 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
specified, 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.
* `--list`:
List information about .lz4 files.
note : current implementation is limited to single-frame .lz4 files.
### Operation modifiers
* `-#`:
Compression level, with # being any value from 1 to 12.
Higher values trade compression 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 compression.
Speed/compression trade-off will vary depending on data to compress.
Decompression speed remains fast at all settings.
* `--fast[=#]`:
Switch to ultra-fast compression levels.
The higher the value, the faster the compression speed, at the cost of some compression ratio.
If `=#` is not present, it defaults to `1`.
This setting overrides compression level if one was set previously.
Similarly, if a compression level is set after `--fast`, it overrides it.
* `--favor-decSpeed`:
Generate compressed data optimized for decompression speed.
Compressed data will be larger as a consequence (typically by ~0.5%),
while decompression speed will be improved by 5-20%, depending on use cases.
This option only works in combination with very high compression levels (>=10).
* `-D dictionaryName`:
Compress, decompress or benchmark using dictionary _dictionaryName_.
Compression and decompression must use the same dictionary to be compatible.
Using a different dictionary during decompression will either
abort due to decompression error, or generate 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.
Can also be used to list multiple files.
`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)<br/>
`-B4`= 64KB ; `-B5`= 256KB ; `-B6`= 1MB ; `-B7`= 4MB
* `-BI`:
Produce independent blocks (default)
* `-BD`:
Blocks depend on predecessors (improves compression ratio, more noticeable on small blocks)
* `--[no-]frame-crc`:
Select frame checksum (default:enabled)
* `--[no-]content-size`:
Header includes original size (default:not present)<br/>
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)<br/>
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
|
