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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 > 500 MB/s per core, linearly scalable with multi-core CPUs. It features an extremely fast decoder, offering 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 (see --rm to erase source file on completion) 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 respectively. Default behaviors can be modified by opt-in commands, detailed below. o lz4 -m makes it possible to provide multiple input filenames, which 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 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 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 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 --[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 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 v1.9.4 August 2022 LZ4(1)