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 > 500 MB/s per core, linearly scalable with multi-core
CPUs. It features an extremely fast decoder, offering 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 (see --rm to
erase source file on completion)
- •
-
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.
- --best
- Set highest compression level. Same as -12.
- --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)
- -BX
- Generate block checksums (default:disabled)
- --[no-]frame-crc
- Select frame checksum (default:enabled)
- --no-crc
- Disable both frame and block checksums
- --[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
Yann Collet