lz4 - lz4, unlz4, lz4cat - Compress or decompress .lz4 files

       Yann Collet

lz4 1.9.2                                           July 2019                                             LZ4(1)

       Report bugs at: https://github.com/lz4/lz4/issues

lz4 is an extremely fast lossless compression algorithm, based on byte-alignedLZ77 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.

   Differencebetweenlz4andgziplz4 supports a command line syntax similar butnotidentical to gzip(1). Differences are :

       •   lz4 compresses a single file by default (see -m for multiple files)

       •   lz4file1file2 means : compress file1 into file2

       •   lz4file.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  stdoutisNottheconsole, 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.

   Concatenationof.lz4files
       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 lz4catfoo.lz4 is equivalent to catfile1file2.

lz4 - lz4, unlz4, lz4cat - Compress or decompress .lz4 files

Shortcommandsconcatenation
       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.

   Multiplecommands
       When multiple contradictory commands are issued on a same command line,  only  the  latest  one  will  be
       applied.

   Operationmode-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.

   Operationmodifiers-#     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).

       -DdictionaryName
              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 -rOtheroptions-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

   Benchmarkmode-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)

lz4 [OPTIONS] [-|INPUT-FILE] OUTPUT-FILEunlz4 is equivalent to lz4-dlz4cat 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.