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

       Yann Collet

lz4 1.10.0                                          July 2024                                             LZ4(1)

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

lz4 is a CLI based on liblz4, an extremely fast implementation  of  lossless  compression  algorithm.  It
       provides  a  default  compression  speed  of  typically  > 500 MB/s per core. Speed can traded for higher
       compression ratio, by increasing the compression level parameter. While decompression is single-threaded,
       it reaches multiple GB/s, generally fast enough to be I/O bound. lz4  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 (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 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 features a behavior closer to the gzip one.

   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. For detailed information on files with multiple frames, use -v.
              --list automatically triggers -m modifier.

   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.

       -T#, --threads=#
              Use  #  threads  for  compression.  When  0, or none provided: automatically determined from nb of
              detected cores.

       --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)

       -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 -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)

   EnvironmentVariables
       It´s possible to pass some parameters to lz4 via environment variables. This can be useful in  situations
       where  lz4  is known to be invoked (from a script for example) but there is no way to pass lz4 parameters
       to influence the compression session. The  environment  variable  has  higher  priority  than  executable
       default, but lower priority than corresponding runtime command. When set as global environment variables,
       it can be a way to enforce personalized defaults different from the executable set ones.

       LZ4_CLEVEL
              specify  a  default  compression  level that lz4 employs for compression when no other compression
              level is specified on command line. Executable default is generally 1.

       LZ4_NBWORKERS
              specify a default number of threads that lz4 will employ for compression.  Executable  default  is
              generally  0,  which means auto-determined based on local cpu. This functionality is only relevant
              when lz4 is compiled with multithreading support. The maximum  number  of  workers  is  capped  at
              LZ4_NBWORKERS_MAX (200 by default).

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.