unlz4

LZ4(1)                           User Commands                          LZ4(1)

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

SYNOPSIS
       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.

DESCRIPTION
       lz4  is  an  extremely  fast  lossless  compression algorithm, based on
       byte-aligned LZ77 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 na-
       tive file format is the .lz4 format.

   Difference between lz4 and gzip
       lz4 supports a  command  line  syntax  similar  but  not  identical  to
       gzip(1). Differences are :

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

       o   lz4 file1 file2 means : compress file1 into file2

       o   lz4  file.lz4  will  default to decompression (use -z to force com-
           pression)

       o   lz4 preserves original files

       o   lz4 shows real-time notification statistics during  compression  or
           decompression of a single file (use -q to silence them)

       o   When  no  destination is specified, result is sent on implicit out-
           put, which depends on stdout status. When stdout is  Not  the  con-
           sole,  it  becomes the implicit output. Otherwise, if stdout is the
           console, the implicit output is filename.lz4.

       o   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  re-
           spectively.

       Default behaviors can be modified by opt-in commands, detailed below.

       o   lz4 -m makes it possible to provide multiple input filenames, which
           will be compressed into files using suffix .lz4. Progress notifica-
           tions 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.

       o   Similarly, lz4 -m -d can decompress multiple *.lz4 files.

       o   It's possible to opt-in to erase source files  on  successful  com-
           pression or decompression, using --rm command.

       o   Consequently, lz4 -m --rm behaves the same as gzip.

   Concatenation of .lz4 files
       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.

OPTIONS
   Short commands concatenation
       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  con-
       catenated. They must be clearly separated by a space.

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

   Operation mode
       -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.

   Operation modifiers
       -#     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  com-
              press. 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  compres-
              sion ratio. If =# is not present, it defaults to 1. This setting
              overrides compression level if one  was  set  previously.  Simi-
              larly,  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. Com-
              pressed  data  will  be  larger  as  a consequence (typically by
              ~0.5%), while decompression speed will be improved by 5-20%, de-
              pending on use cases. This option only works in combination with
              very high compression levels (>=10).

       -D dictionaryName
              Compress, decompress or benchmark using  dictionary  dictionary-
              Name. Compression and decompression must use the same dictionary
              to be compatible. Using a different dictionary during decompres-
              sion 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  prompt-
              ing.

              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 (mul-
              tiple 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 std-
              out)

       -l     Use Legacy format (typically for Linux Kernel compression)
              Note : -l is not compatible with -m (--multiple) nor -r

   Other options
       -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

   Benchmark mode
       -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)

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

AUTHOR
       Yann Collet

lz4 1.9.2                          July 2019                            LZ4(1)