251 lines
6.0 KiB
Groff
251 lines
6.0 KiB
Groff
\."
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\." lz4.1: This is a manual page for 'lz4' program. This file is part of the
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\." lz4 <http://www.lz4.org/> project.
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\." Author: Yann Collet
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\."
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.
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\." No hyphenation
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.hy 0
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.nr HY 0
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.
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.TH lz4 "1" "2015-03-21" "lz4" "User Commands"
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.SH NAME
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\fBlz4, unlz4, lz4cat\fR \- Compress or decompress .lz4 files
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.SH SYNOPSIS
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.TP 5
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\fBlz4\fR [\fBOPTIONS\fR] [-|INPUT-FILE] <OUTPUT-FILE>
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.PP
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.B unlz4
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is equivalent to
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.BR "lz4 \-d"
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.br
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.B lz4cat
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is equivalent to
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.BR "lz4 \-dcfm"
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.br
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.PP
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When writing scripts that need to decompress files,
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it is recommended to always use the name
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.B lz4
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with appropriate arguments
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.RB ( "lz4 \-d"
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or
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.BR "lz4 \-dc" )
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instead of the names
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.B unlz4
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and
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.BR lz4cat .
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.SH DESCRIPTION
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.PP
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\fBlz4\fR is an extremely fast lossless compression algorithm,
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based on \fBbyte-aligned LZ77\fR family of compression scheme.
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\fBlz4\fR offers compression speeds of 400 MB/s per core, linearly scalable with multi-core CPUs.
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It features an extremely fast decoder, with speed in multiple GB/s per core,
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typically reaching RAM speed limit on multi-core systems.
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The native file format is the
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.B .lz4
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format.
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.B lz4
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supports a command line syntax similar \fIbut not identical\fR to
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.BR gzip (1).
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Differences are :
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\fBlz4\fR preserves original files
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\fBlz4\fR compresses a single file by default (use \fB-m\fR for multiple files)
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\fBlz4 file1 file2\fR means : compress file1 \fIinto\fR file2
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When no destination name is provided, compressed file name receives a \fB.lz4\fR suffix
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When no destination name is provided, if \fBstdout\fR is \fInot\fR the console, it becomes the output (like a silent \fB-c\fR)
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Therefore \fBlz4 file > /dev/null\fR will not create \fBfile.lz4\fR
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\fBlz4 file\fR shows real-time statistics during compression (use \fB-q\fR to silent them)
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Default behaviors can be modified by opt-in commands, described below.
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\fBlz4 --quiet --multiple\fR more closely mimics \fBgzip\fR behavior.
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.SS "Concatenation of .lz4 files"
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It is possible to concatenate
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.B .lz4
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files as is.
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.B lz4
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will decompress such files as if they were a single
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.B .lz4
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file. For example:
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lz4 file1 > foo.lz4
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lz4 file2 >> foo.lz4
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then
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lz4cat foo.lz4
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is equivalent to :
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cat file1 file2
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.PP
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.SH OPTIONS
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.
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.SS "Short commands concatenation"
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In some cases, some options can be expressed using short command
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.B "-x"
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or long command
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.B "--long-word" .
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Short commands can be concatenated together. For example,
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.B "-d -c"
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is equivalent to
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.B "-dc" .
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Long commands cannot be concatenated.
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They must be clearly separated by a space.
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.SS "Multiple commands"
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When multiple contradictory commands are issued on a same command line,
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only the latest one will be applied.
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.
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.SS "Operation mode"
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.TP
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.BR \-z ", " \-\-compress
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Compress.
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This is the default operation mode
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when no operation mode option is specified ,
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no other operation mode is implied from the command name
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(for example,
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.B unlz4
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implies
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.B \-\-decompress ),
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nor from the input file name
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(for example, a file extension
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.B .lz4
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implies
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.B \-\-decompress
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by default).
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.B -z
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can also be used to force compression of an already compressed
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.B .lz4
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file.
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.TP
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.BR \-d ", " \-\-decompress ", " \-\-uncompress
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Decompress.
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.B --decompress
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is also the default operation when the input filename has an
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.B .lz4
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extension.
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.TP
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.BR \-t ", " \-\-test
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Test the integrity of compressed
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.B .lz4
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files.
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The decompressed data is discarded.
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No files are created nor removed.
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.TP
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.BR \-b#
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Benchmark mode, using # compression level.
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.
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.SS "Operation modifiers"
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.TP
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.B \-#
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compression level, with # being any value from 1 to 16.
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Higher values trade compression speed for compression ratio.
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Values above 16 are considered the same as 16.
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Recommended values are 1 for fast compression (default), and 9 for high compression.
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Speed/compression trade-off will vary depending on data to compress.
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Decompression speed remains fast at all settings.
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.TP
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.BR \-f ", " --[no-]force
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This option has several effects:
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.RS
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.IP \(bu 3
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If the target file already exists,
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overwrite it without prompting.
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.IP \(bu 3
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When used with
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.B \-\-decompress
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and
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.B lz4
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cannot recognize the type of the source file,
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copy the source file as is to standard output.
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This allows
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.B lz4cat
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.B \-\-force
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to be used like
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.BR cat (1)
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for files that have not been compressed with
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.BR lz4 .
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.RE
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.TP
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.BR \-c ", " \--stdout ", " \--to-stdout
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force write to standard output, even if it is the console
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.TP
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.BR \-m ", " \--multiple
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Multiple file names.
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By default, the second filename is used as the destination filename for the compressed file.
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With
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.B -m
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, it is possible to specify any number of input filenames. Each of them will be compressed
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independently, and the resulting name of each compressed file will be
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.B filename.lz4
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.
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.TP
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.B \-B#
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block size [4-7](default : 7)
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B4= 64KB ; B5= 256KB ; B6= 1MB ; B7= 4MB
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.TP
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.B \-BD
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block dependency (improves compression ratio on small blocks)
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.TP
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.B \--[no-]frame-crc
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select frame checksum (default:enabled)
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.TP
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.B \--[no-]content-size
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header includes original size (default:not present)
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Note : this option can only be activated when the original size can be determined,
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hence for a file. It won't work with unknown source size, such as stdin or pipe.
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.TP
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.B \--[no-]sparse
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sparse mode support (default:enabled on file, disabled on stdout)
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.TP
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.B \-l
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use Legacy format (useful for Linux Kernel compression)
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.
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.SS "Other options"
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.TP
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.BR \-v ", " --verbose
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verbose mode
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.TP
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.BR \-q ", " --quiet
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suppress warnings and real-time statistics; specify twice to suppress errors too
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.TP
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.B \-h/\-H ", " --help
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display help/long help and exit
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.TP
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.BR \-V ", " \--version
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display Version number and exit
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.TP
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.BR \-k ", " \--keep
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Don't delete source file.
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This is default behavior anyway, so this option is just for compatibility with gzip/xz.
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.
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.SS "Benchmark mode"
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.TP
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.B \-b#
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benchmark file(s), using # compression level
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.TP
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.B \-e#
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benchmark multiple compression levels, from b# to e# (included)
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.TP
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.B \-i#
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minimum evaluation in seconds [1-9] (default : 3)
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.TP
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.B \-r
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operate recursively on directories
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.SH BUGS
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Report bugs at: https://github.com/Cyan4973/lz4/issues
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.SH AUTHOR
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Yann Collet
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