127 lines
3.6 KiB
Groff
127 lines
3.6 KiB
Groff
\"
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\" zstd.1: This is a manual page for 'zstd' program. This file is part of the
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\" zstd <http://www.zstd.net/> project.
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\" Author: Yann Collet
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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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.TH zstd "1" "2015-08-22" "zstd" "User Commands"
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.SH NAME
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\fBzstd, unzstd, zstdcat\fR - Compress or decompress .zst files
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.SH SYNOPSIS
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.TP 5
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\fBzstd\fR [\fBOPTIONS\fR] [-|INPUT-FILE] [-o <OUTPUT-FILE>]
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.PP
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.B unzstd
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is equivalent to
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.BR "zstd \-d"
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.br
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.B zstdcat
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is equivalent to
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.BR "zstd \-dc"
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.br
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.SH DESCRIPTION
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.PP
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\fBzstd\fR is a fast lossless compression algorithm.
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It is based on the \fBLZ77\fR family, with further FSE & huff0 entropy stages.
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\fBzstd\fR offers configurable compression speed, with fast modes at > 200 MB/s per core.
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It also features a very fast decoder, with speed > 500 MB/s per core.
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\fBzstd\fR command line is generally similar to gzip, but features the following differences :
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- Original files are preserved
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- By default, when compressing a single file, \fBzstd\fR displays progress notifications and result summary.
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Use \fB-q\fR to turn them off
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\fBzstd\fR supports the following options :
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.SH OPTIONS
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.TP
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.B \-#
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# compression level [1-21] (default:1)
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.TP
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.BR \-d ", " --decompress
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decompression
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.TP
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.B \-D file
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use `file` as Dictionary to compress or decompress FILE(s)
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.TP
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.B \-o file
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save result into `file` (only possible with a single input FILE)
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.TP
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.BR \-f ", " --force
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overwrite output without prompting
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.TP
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.BR \-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 \-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 notifications; specify twice to suppress errors too
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.TP
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.BR \-c ", " --stdout
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force write to standard output, even if it is the console
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.SH DICTIONARY
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.PP
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\fBzstd\fR offers \fIdictionary\fR compression, useful for very small files and messages.
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It's possible to train \fBzstd\fR with some samples, the result of which is saved into a file called `dictionary`.
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Then during compression and decompression, make reference to the same dictionary.
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It will improve compression ratio of small files.
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Typical gains range from ~10% (at 64KB) to x5 better (at <1KB).
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.TP
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.B \--train FILEs
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use FILEs as training set to create a dictionary.
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The training set should contain a lot of small files (> 100).
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and weight typically 100x the target dictionary size
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(for example, 10 MB for a 100 KB dictionary)
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.TP
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.B \-o file
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dictionary saved into `file` (default: dictionary)
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.TP
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.B \--maxdict #
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limit dictionary to specified size (default : 112640)
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.TP
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.B \--dictID #
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A dictionary ID is a locally unique ID that a decoder can use to verify it is using the right dictionary.
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By default, zstd will create a 4-bytes random number ID.
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It's possible to give a precise number instead.
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Short numbers have an advantage : an ID < 256 will only need 1 byte in the compressed frame header,
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and an ID < 65536 will only need 2 bytes. This compares favorably to 4 bytes default.
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However, it's up to the dictionary manager to not assign twice the same ID to 2 different dictionaries.
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.TP
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.B \-s#
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dictionary selectivity level (default: 9)
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the smaller the value, the denser the dictionary, improving its efficiency but reducing its possible maximum size.
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.SH BENCHMARK
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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 \-i#
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iteration loops [1-9](default : 3), benchmark mode only
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.TP
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.B \-B#
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cut file into independent blocks of size # (default: no block)
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.TP
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.B \-r#
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test all compression levels from 1 to # (default: disabled)
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.SH BUGS
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Report bugs at:- https://github.com/Cyan4973/zstd/issues
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.SH AUTHOR
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Yann Collet
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