When writing scripts that need to decompress files, it is recommended to always use the name \fBlz4\fR with appropriate arguments (\fBlz4 \-d\fR or \fBlz4 \-dc\fR) instead of the names \fBunlz4\fR and \fBlz4cat\fR\.
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.SH"DESCRIPTION"
\fBlz4\fR is an extremely fast lossless compression algorithm, based on \fBbyte\-aligned LZ77\fR family of compression scheme\.\fBlz4\fR 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 \fB\.lz4\fR format\.
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.SS"Difference between lz4 and gzip"
\fBlz4\fR supports a command line syntax similar \fIbut not identical\fR to \fBgzip(1)\fR\. Differences are :
As a consequence of previous rules, note the following example : \fBlz4 file | consumer\fR sends compressed data to \fBconsumer\fR through \fBstdout\fR, hence it does \fInot\fR create \fBfile\.lz4\fR\.
Another consequence of those rules is that to run \fBlz4\fR under \fBnohup\fR, you should provide a destination file: \fBnohup lz4 file file\.lz4\fR, because \fBnohup\fR writes the specified command\'s output to a file\.
\fBlz4 \-m\fR makes it possible to provide multiple input filenames, which will be compressed into files using suffix \fB\.lz4\fR\. Progress notifications are also disabled by default (use \fB\-v\fR to enable them)\. This mode has a behavior which more closely mimics \fBgzip\fR command line, with the main remaining difference being that source files are preserved by default\.
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.IP"\(bu"4
Similarly, \fBlz4 \-m \-d\fR can decompress multiple \fB*\.lz4\fR files\.
In some cases, some options can be expressed using short command \fB\-x\fR or long command \fB\-\-long\-word\fR\. Short commands can be concatenated together\. For example, \fB\-d \-c\fR is equivalent to \fB\-dc\fR\. Long commands cannot be concatenated\. They must be clearly separated by a space\.
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, \fBunlz4\fR implies \fB\-\-decompress\fR), nor from the input file name (for example, a file extension \fB\.lz4\fR implies \fB\-\-decompress\fR by default)\.\fB\-z\fR can also be used to force compression of an already compressed \fB\.lz4\fR file\.
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\.
Switch to ultra\-fast compression levels\. The higher the value, the faster the compression speed, at the cost of some compression ratio\. If \fB=#\fR is not present, it defaults to \fB1\fR\. This setting overrides compression level if one was set previously\. Similarly, if a compression level is set after \fB\-\-fast\fR, it overrides it\.
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.TP
\fB\-\-favor\-decSpeed\fR
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)\.
Compress, decompress or benchmark using dictionary \fIdictionaryName\fR\. 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\.
If the target file already exists, overwrite it without prompting\.
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.IP
When used with \fB\-\-decompress\fR and \fBlz4\fR cannot recognize the type of the source file, copy the source file as is to standard output\. This allows \fBlz4cat \-\-force\fR to be used like \fBcat (1)\fR for files that have not been compressed with \fBlz4\fR\.
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.TP
\fB\-c\fR\fB\-\-stdout\fR\fB\-\-to\-stdout\fR
Force write to standard output, even if it is the console\.
Multiple input files\. Compressed file names will be appended a \fB\.lz4\fR suffix\. This mode also reduces notification level\.\fBlz4 \-m\fR has a behavior equivalent to \fBgzip \-k\fR (it preserves source files by default)\.
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.TP
\fB\-r\fR
operate recursively on directories\. This mode also sets \fB\-m\fR (multiple input files)\.
Header includes original size (default:not present)
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.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\.
