     LZ4(1)                           lz4 1.9.2                           LZ4(1)
     User Commands                                                 User Commands

                                      July 2019

     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
              compression)

          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
              output, which depends on stdout status. When stdout is Not the
              console, 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

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     LZ4(1)                           lz4 1.9.2                           LZ4(1)
     User Commands                                                 User Commands

                                      July 2019

              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
              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.

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

          o   It's possible to opt-in to erase source files on successful
              compression 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
          concatenated. 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

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     LZ4(1)                           lz4 1.9.2                           LZ4(1)
     User Commands                                                 User Commands

                                      July 2019

               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
               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).

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

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     LZ4(1)                           lz4 1.9.2                           LZ4(1)
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               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 -r

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     LZ4(1)                           lz4 1.9.2                           LZ4(1)
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                                      July 2019

        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

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