1LZ4(1) User Commands LZ4(1)
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6 lz4 - lz4, unlz4, lz4cat - Compress or decompress .lz4 files
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9 lz4 [OPTIONS] [-|INPUT-FILE] OUTPUT-FILE
10 unlz4 is equivalent to lz4 -d
12 lz4cat is equivalent to lz4 -dcfm
14 When writing scripts that need to decompress files, it is recommended
16 to always use the name lz4 with appropriate arguments (lz4 -d or lz4
17 -dc) instead of the names unlz4 and lz4cat.
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20 lz4 is an extremely fast lossless compression algorithm, based on
21 byte-aligned LZ77 family of compression scheme. lz4 offers compression
22 speeds of 400 MB/s per core, linearly scalable with multi-core CPUs. It
23 features an extremely fast decoder, with speed in multiple GB/s per
24 core, typically reaching RAM speed limit on multi-core systems. The na‐
25 tive file format is the .lz4 format.
26 Difference between lz4 and gzip
28 lz4 supports a command line syntax similar but not identical to
29 gzip(1). Differences are :
30 • lz4 compresses a single file by default (see -m for multiple files)
32 • lz4 file1 file2 means : compress file1 into file2
34 • lz4 file.lz4 will default to decompression (use -z to force com‐
36 pression)
37 • lz4 preserves original files
39 • lz4 shows real-time notification statistics during compression or
41 decompression of a single file (use -q to silence them)
42 • When no destination is specified, result is sent on implicit out‐
44 put, which depends on stdout status. When stdout is Not the con‐
45 sole, it becomes the implicit output. Otherwise, if stdout is the
46 console, the implicit output is filename.lz4.
47 • It is considered bad practice to rely on implicit output in
49 scripts. because the script´s environment may change. Always use
50 explicit output in scripts. -c ensures that output will be stdout.
51 Conversely, providing a destination name, or using -m ensures that
52 the output will be either the specified name, or filename.lz4 re‐
53 spectively.
54 Default behaviors can be modified by opt-in commands, detailed below.
58 • lz4 -m makes it possible to provide multiple input filenames, which
60 will be compressed into files using suffix .lz4. Progress notifica‐
61 tions become disabled by default (use -v to enable them). This mode
62 has a behavior which more closely mimics gzip command line, with
63 the main remaining difference being that source files are preserved
64 by default.
65 • Similarly, lz4 -m -d can decompress multiple *.lz4 files.
67 • It´s possible to opt-in to erase source files on successful com‐
69 pression or decompression, using --rm command.
70 • Consequently, lz4 -m --rm behaves the same as gzip.
72 Concatenation of .lz4 files
76 It is possible to concatenate .lz4 files as is. lz4 will decompress
77 such files as if they were a single .lz4 file. For example:
78 lz4 file1 > foo.lz4
82 lz4 file2 >> foo.lz4
83 Then lz4cat foo.lz4 is equivalent to cat file1 file2.
87
89 Short commands concatenation
90 In some cases, some options can be expressed using short command -x or
91 long command --long-word. Short commands can be concatenated together.
92 For example, -d -c is equivalent to -dc. Long commands cannot be con‐
93 catenated. They must be clearly separated by a space.
94 Multiple commands
96 When multiple contradictory commands are issued on a same command line,
97 only the latest one will be applied.
98 Operation mode
100 -z --compress
101 Compress. This is the default operation mode when no operation
102 mode option is specified, no other operation mode is implied
103 from the command name (for example, unlz4 implies --decompress),
104 nor from the input file name (for example, a file extension .lz4
105 implies --decompress by default). -z can also be used to force
106 compression of an already compressed .lz4 file.
107 -d --decompress --uncompress
109 Decompress. --decompress is also the default operation when the
110 input filename has an .lz4 extension.
111 -t --test
113 Test the integrity of compressed .lz4 files. The decompressed
114 data is discarded. No files are created nor removed.
115 -b# Benchmark mode, using # compression level.
117 --list List information about .lz4 files. note : current implementation
119 is limited to single-frame .lz4 files.
120 Operation modifiers
122 -# Compression level, with # being any value from 1 to 12. Higher
123 values trade compression speed for compression ratio. Values
124 above 12 are considered the same as 12. Recommended values are 1
125 for fast compression (default), and 9 for high compression.
126 Speed/compression trade-off will vary depending on data to com‐
127 press. Decompression speed remains fast at all settings.
128 --fast[=#]
130 Switch to ultra-fast compression levels. The higher the value,
131 the faster the compression speed, at the cost of some compres‐
132 sion ratio. If =# is not present, it defaults to 1. This setting
133 overrides compression level if one was set previously. Simi‐
134 larly, if a compression level is set after --fast, it overrides
135 it.
136 --best Set highest compression level. Same as -12.
138 --favor-decSpeed
140 Generate compressed data optimized for decompression speed. Com‐
141 pressed data will be larger as a consequence (typically by
142 ~0.5%), while decompression speed will be improved by 5-20%, de‐
143 pending on use cases. This option only works in combination with
144 very high compression levels (>=10).
145 -D dictionaryName
147 Compress, decompress or benchmark using dictionary dictionary‐
148 Name. Compression and decompression must use the same dictionary
149 to be compatible. Using a different dictionary during decompres‐
150 sion will either abort due to decompression error, or generate a
151 checksum error.
152 -f --[no-]force
154 This option has several effects:
155 If the target file already exists, overwrite it without prompt‐
157 ing.
158 When used with --decompress and lz4 cannot recognize the type of
160 the source file, copy the source file as is to standard output.
161 This allows lz4cat --force to be used like cat (1) for files
162 that have not been compressed with lz4.
163 -c --stdout --to-stdout
165 Force write to standard output, even if it is the console.
166 -m --multiple
168 Multiple input files. Compressed file names will be appended a
169 .lz4 suffix. This mode also reduces notification level. Can also
170 be used to list multiple files. lz4 -m has a behavior equivalent
171 to gzip -k (it preserves source files by default).
172 -r operate recursively on directories. This mode also sets -m (mul‐
174 tiple input files).
175 -B# Block size [4-7](default : 7)
177 -B4= 64KB ; -B5= 256KB ; -B6= 1MB ; -B7= 4MB
178 -BI Produce independent blocks (default)
180 -BD Blocks depend on predecessors (improves compression ratio, more
182 noticeable on small blocks)
183 --[no-]frame-crc
185 Select frame checksum (default:enabled)
186 --[no-]content-size
188 Header includes original size (default:not present)
189 Note : this option can only be activated when the original size
190 can be determined, hence for a file. It won´t work with unknown
191 source size, such as stdin or pipe.
192 --[no-]sparse
194 Sparse mode support (default:enabled on file, disabled on std‐
195 out)
196 -l Use Legacy format (typically for Linux Kernel compression)
198 Note : -l is not compatible with -m (--multiple) nor -r
199 Other options
201 -v --verbose
202 Verbose mode
203 -q --quiet
205 Suppress warnings and real-time statistics; specify twice to
206 suppress errors too
207 -h -H --help
209 Display help/long help and exit
210 -V --version
212 Display Version number and exit
213 -k --keep
215 Preserve source files (default behavior)
216 --rm Delete source files on successful compression or decompression
218 -- Treat all subsequent arguments as files
220 Benchmark mode
222 -b# Benchmark file(s), using # compression level
223 -e# Benchmark multiple compression levels, from b# to e# (included)
225 -i# Minimum evaluation time in seconds [1-9] (default : 3)
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229 Report bugs at: https://github.com/lz4/lz4/issues
230
232 Yann Collet
233lz4 1.9.2 July 2019 LZ4(1)