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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
       native 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
           respectively.



       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%,
              depending 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)

lz4 1.9.2 - Generated Tue Sep 3 18:15:34 CDT 2019
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