Merge pull request #2120 from facebook/clevel_doc
updated zstd CLI documentation
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Yann Collet
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@ -10,7 +10,7 @@ There are however other Makefile targets that create different variations of CLI
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- `zstd-decompress` : version of CLI which can only decompress zstd format
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#### Compilation variables
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### Compilation variables
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`zstd` scope can be altered by modifying the following `make` variables :
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- __HAVE_THREAD__ : multithreading is automatically enabled when `pthread` is detected.
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@ -61,6 +61,24 @@ There are however other Makefile targets that create different variations of CLI
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In which case, linking stage will fail if `lz4` library cannot be found.
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This is useful to prevent silent feature disabling.
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- __ZSTD_NOBENCH__ : `zstd` cli will be compiled without its integrated benchmark module.
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This can be useful to produce smaller binaries.
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In this case, the corresponding unit can also be excluded from compilation target.
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- __ZSTD_NODICT__ : `zstd` cli will be compiled without support for the integrated dictionary builder.
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This can be useful to produce smaller binaries.
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In this case, the corresponding unit can also be excluded from compilation target.
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- __ZSTD_NOCOMPRESS__ : `zstd` cli will be compiled without support for compression.
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The resulting binary will only be able to decompress files.
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This can be useful to produce smaller binaries.
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A corresponding `Makefile` target using this ability is `zstd-decompress`.
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- __ZSTD_NODECOMPRESS__ : `zstd` cli will be compiled without support for decompression.
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The resulting binary will only be able to compress files.
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This can be useful to produce smaller binaries.
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A corresponding `Makefile` target using this ability is `zstd-compress`.
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- __BACKTRACE__ : `zstd` can display a stack backtrace when execution
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generates a runtime exception. By default, this feature may be
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degraded/disabled on some platforms unless additional compiler directives are
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@ -69,11 +87,11 @@ There are however other Makefile targets that create different variations of CLI
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Example : `make zstd BACKTRACE=1`
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#### Aggregation of parameters
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### Aggregation of parameters
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CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`.
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#### Symlink shortcuts
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### Symlink shortcuts
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It's possible to invoke `zstd` through a symlink.
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When the name of the symlink has a specific value, it triggers an associated behavior.
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- `zstdmt` : compress using all cores available on local system.
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@ -86,7 +104,7 @@ When the name of the symlink has a specific value, it triggers an associated beh
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- `ungz`, `unxz` and `unlzma` will do the same, and will also remove source file by default (use `--keep` to preserve).
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#### Dictionary builder in Command Line Interface
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### Dictionary builder in Command Line Interface
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Zstd offers a training mode, which can be used to tune the algorithm for a selected
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type of data, by providing it with a few samples. The result of the training is stored
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in a file selected with the `-o` option (default name is `dictionary`),
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@ -106,7 +124,7 @@ Usage of the dictionary builder and created dictionaries with CLI:
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3. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName`
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#### Benchmark in Command Line Interface
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### Benchmark in Command Line Interface
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CLI includes in-memory compression benchmark module for zstd.
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The benchmark is conducted using given filenames. The files are read into memory and joined together.
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It makes benchmark more precise as it eliminates I/O overhead.
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@ -118,81 +136,84 @@ One can select compression levels starting from `-b` and ending with `-e`.
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The `-i` parameter selects minimal time used for each of tested levels.
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#### Usage of Command Line Interface
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### Usage of Command Line Interface
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The full list of options can be obtained with `-h` or `-H` parameter:
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```
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Usage :
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zstd [args] [FILE(s)] [-o file]
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Usage :
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zstd [args] [FILE(s)] [-o file]
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FILE : a filename
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FILE : a filename
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with no FILE, or when FILE is - , read standard input
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Arguments :
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-# : # compression level (1-19, default: 3)
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-d : decompression
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-D file: use `file` as Dictionary
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-o file: result stored into `file` (only if 1 input file)
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-f : overwrite output without prompting and (de)compress links
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--rm : remove source file(s) after successful de/compression
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-k : preserve source file(s) (default)
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-h/-H : display help/long help and exit
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Arguments :
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-# : # compression level (1-19, default: 3)
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-d : decompression
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-D file: use `file` as Dictionary
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-o file: result stored into `file` (only if 1 input file)
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-f : overwrite output without prompting and (de)compress links
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--rm : remove source file(s) after successful de/compression
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-k : preserve source file(s) (default)
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-h/-H : display help/long help and exit
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Advanced arguments :
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-V : display Version number and exit
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Advanced arguments :
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-V : display Version number and exit
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-v : verbose mode; specify multiple times to increase verbosity
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-q : suppress warnings; specify twice to suppress errors too
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-c : force write to standard output, even if it is the console
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-l : print information about zstd compressed files
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--exclude-compressed: only compress files that are not previously compressed
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-l : print information about zstd compressed files
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--exclude-compressed: only compress files that are not previously compressed
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--ultra : enable levels beyond 19, up to 22 (requires more memory)
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--long[=#]: enable long distance matching with given window log (default: 27)
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--fast[=#]: switch to very fast compression levels (default: 1)
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--adapt : dynamically adapt compression level to I/O conditions
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--stream-size=# : optimize compression parameters for streaming input of given number of bytes
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--adapt : dynamically adapt compression level to I/O conditions
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--stream-size=# : optimize compression parameters for streaming input of given number of bytes
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--size-hint=# optimize compression parameters for streaming input of approximately this size
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--target-compressed-block-size=# : make compressed block near targeted size
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-T# : spawns # compression threads (default: 1, 0==# cores)
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-B# : select size of each job (default: 0==automatic)
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--rsyncable : compress using a rsync-friendly method (-B sets block size)
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--target-compressed-block-size=# : make compressed block near targeted size
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-T# : spawns # compression threads (default: 1, 0==# cores)
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-B# : select size of each job (default: 0==automatic)
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--rsyncable : compress using a rsync-friendly method (-B sets block size)
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--no-dictID : don't write dictID into header (dictionary compression)
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--[no-]check : integrity check (default: enabled)
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--[no-]compress-literals : force (un)compressed literals
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-r : operate recursively on directories
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--output-dir-flat[=directory]: all resulting files stored into `directory`.
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--format=zstd : compress files to the .zst format (default)
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--format=gzip : compress files to the .gz format
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--test : test compressed file integrity
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--[no-]check : integrity check (default: enabled)
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--[no-]compress-literals : force (un)compressed literals
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-r : operate recursively on directories
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--output-dir-flat[=directory]: all resulting files stored into `directory`.
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--format=zstd : compress files to the .zst format (default)
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--format=gzip : compress files to the .gz format
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--test : test compressed file integrity
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--[no-]sparse : sparse mode (default: disabled)
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-M# : Set a memory usage limit for decompression
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--no-progress : do not display the progress bar
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-- : All arguments after "--" are treated as files
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-M# : Set a memory usage limit for decompression
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--no-progress : do not display the progress bar
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-- : All arguments after "--" are treated as files
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Dictionary builder :
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--train ## : create a dictionary from a training set of files
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Dictionary builder :
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--train ## : create a dictionary from a training set of files
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--train-cover[=k=#,d=#,steps=#,split=#,shrink[=#]] : use the cover algorithm with optional args
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--train-fastcover[=k=#,d=#,f=#,steps=#,split=#,accel=#,shrink[=#]] : use the fast cover algorithm with optional args
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--train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9)
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-o file : `file` is dictionary name (default: dictionary)
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--maxdict=# : limit dictionary to specified size (default: 112640)
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-o file : `file` is dictionary name (default: dictionary)
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--maxdict=# : limit dictionary to specified size (default: 112640)
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--dictID=# : force dictionary ID to specified value (default: random)
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Benchmark arguments :
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-b# : benchmark file(s), using # compression level (default: 3)
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Benchmark arguments :
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-b# : benchmark file(s), using # compression level (default: 3)
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-e# : test all compression levels from -bX to # (default: 1)
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-i# : minimum evaluation time in seconds (default: 3s)
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-i# : minimum evaluation time in seconds (default: 3s)
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-B# : cut file into independent blocks of size # (default: no block)
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--priority=rt : set process priority to real-time
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--priority=rt : set process priority to real-time
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```
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#### Restricted usage of Environment Variables
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Using environment variables to set parameters has security implications.
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Therefore, this avenue is intentionally restricted.
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Only `ZSTD_CLEVEL` is supported currently, for setting compression level.
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`ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range).
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If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message.
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`ZSTD_CLEVEL` just replaces the default compression level (`3`).
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It can be overridden by corresponding command line arguments.
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### Passing parameters through Environment Variables
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`ZSTD_CLEVEL` can be used to modify the default compression level of `zstd`
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(usually set to `3`) to another value between 1 and 19 (the "normal" range).
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This can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments.
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One such scenario is `tar --zstd`.
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As `ZSTD_CLEVEL` only replaces the default compression level,
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it can then be overridden by corresponding command line arguments.
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#### Long distance matching mode
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There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner.
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Using environment variables for this purpose has security implications.
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Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL`.
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### Long distance matching mode
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The long distance matching mode, enabled with `--long`, is designed to improve
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the compression ratio for files with long matches at a large distance (up to the
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maximum window size, `128 MiB`) while still maintaining compression speed.
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@ -216,12 +237,12 @@ Compression Speed vs Ratio | Decompression Speed
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| Method | Compression ratio | Compression speed | Decompression speed |
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|:-------|------------------:|-------------------------:|---------------------------:|
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| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` |
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| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` |
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| `zstd -5` | `5.826` | `124.9 MB/s` | `674.0 MB/s` |
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| `zstd -10` | `6.504` | `29.5 MB/s` | `771.3 MB/s` |
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| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` |
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| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s`|
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| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s`|
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| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s` |
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| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s` |
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On this file, the compression ratio improves significantly with minimal impact
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on compression speed, and the decompression speed doubles.
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@ -243,7 +264,8 @@ The below table illustrates this on the [Silesia compression corpus].
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| `zstd -10` | `3.523` | `16.4 MB/s` | `489.2 MB/s` |
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| `zstd -10 --long`| `3.566` | `16.2 MB/s` | `415.7 MB/s` |
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#### zstdgrep
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### zstdgrep
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`zstdgrep` is a utility which makes it possible to `grep` directly a `.zst` compressed file.
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It's used the same way as normal `grep`, for example :
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