lz4 - lz4, unlz4, lz4cat - Compress or decompress .lz4 files
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.
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.
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.
-
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.
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.
When multiple contradictory commands are issued on a same command line, only the
latest one will be applied.
- -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.
- -#
- 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)
-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)
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
- -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
- -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)
Report bugs at: https://github.com/lz4/lz4/issues