1Command Line Interface for Zstandard library 2============================================ 3 4Command Line Interface (CLI) can be created using the `make` command without any additional parameters. 5There are however other Makefile targets that create different variations of CLI: 6- `zstd` : default CLI supporting gzip-like arguments; includes dictionary builder, benchmark, and support for decompression of legacy zstd formats 7- `zstd_nolegacy` : Same as `zstd` but without support for legacy zstd formats 8- `zstd-small` : CLI optimized for minimal size; no dictionary builder, no benchmark, and no support for legacy zstd formats 9- `zstd-compress` : version of CLI which can only compress into zstd format 10- `zstd-decompress` : version of CLI which can only decompress zstd format 11 12 13#### Compilation variables 14`zstd` scope can be altered by modifying the following `make` variables : 15 16- __HAVE_THREAD__ : multithreading is automatically enabled when `pthread` is detected. 17 It's possible to disable multithread support, by setting `HAVE_THREAD=0`. 18 Example : `make zstd HAVE_THREAD=0` 19 It's also possible to force multithread support, using `HAVE_THREAD=1`. 20 In which case, linking stage will fail if neither `pthread` nor `windows.h` library can be found. 21 This is useful to ensure this feature is not silently disabled. 22 23- __ZSTD_LEGACY_SUPPORT__ : `zstd` can decompress files compressed by older versions of `zstd`. 24 Starting v0.8.0, all versions of `zstd` produce frames compliant with the [specification](../doc/zstd_compression_format.md), and are therefore compatible. 25 But older versions (< v0.8.0) produced different, incompatible, frames. 26 By default, `zstd` supports decoding legacy formats >= v0.4.0 (`ZSTD_LEGACY_SUPPORT=4`). 27 This can be altered by modifying this compilation variable. 28 `ZSTD_LEGACY_SUPPORT=1` means "support all formats >= v0.1.0". 29 `ZSTD_LEGACY_SUPPORT=2` means "support all formats >= v0.2.0", and so on. 30 `ZSTD_LEGACY_SUPPORT=0` means _DO NOT_ support any legacy format. 31 if `ZSTD_LEGACY_SUPPORT >= 8`, it's the same as `0`, since there is no legacy format after `7`. 32 Note : `zstd` only supports decoding older formats, and cannot generate any legacy format. 33 34- __HAVE_ZLIB__ : `zstd` can compress and decompress files in `.gz` format. 35 This is ordered through command `--format=gzip`. 36 Alternatively, symlinks named `gzip` or `gunzip` will mimic intended behavior. 37 `.gz` support is automatically enabled when `zlib` library is detected at build time. 38 It's possible to disable `.gz` support, by setting `HAVE_ZLIB=0`. 39 Example : `make zstd HAVE_ZLIB=0` 40 It's also possible to force compilation with zlib support, `using HAVE_ZLIB=1`. 41 In which case, linking stage will fail if `zlib` library cannot be found. 42 This is useful to prevent silent feature disabling. 43 44- __HAVE_LZMA__ : `zstd` can compress and decompress files in `.xz` and `.lzma` formats. 45 This is ordered through commands `--format=xz` and `--format=lzma` respectively. 46 Alternatively, symlinks named `xz`, `unxz`, `lzma`, or `unlzma` will mimic intended behavior. 47 `.xz` and `.lzma` support is automatically enabled when `lzma` library is detected at build time. 48 It's possible to disable `.xz` and `.lzma` support, by setting `HAVE_LZMA=0` . 49 Example : `make zstd HAVE_LZMA=0` 50 It's also possible to force compilation with lzma support, using `HAVE_LZMA=1`. 51 In which case, linking stage will fail if `lzma` library cannot be found. 52 This is useful to prevent silent feature disabling. 53 54- __HAVE_LZ4__ : `zstd` can compress and decompress files in `.lz4` formats. 55 This is ordered through commands `--format=lz4`. 56 Alternatively, symlinks named `lz4`, or `unlz4` will mimic intended behavior. 57 `.lz4` support is automatically enabled when `lz4` library is detected at build time. 58 It's possible to disable `.lz4` support, by setting `HAVE_LZ4=0` . 59 Example : `make zstd HAVE_LZ4=0` 60 It's also possible to force compilation with lz4 support, using `HAVE_LZ4=1`. 61 In which case, linking stage will fail if `lz4` library cannot be found. 62 This is useful to prevent silent feature disabling. 63 64 65#### Aggregation of parameters 66CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`. 67 68 69#### Symlink shortcuts 70It's possible to invoke `zstd` through a symlink. 71When the name of the symlink has a specific value, it triggers an associated behavior. 72- `zstdmt` : compress using all cores available on local system. 73- `zcat` : will decompress and output target file using any of the supported formats. `gzcat` and `zstdcat` are also equivalent. 74- `gzip` : if zlib support is enabled, will mimic `gzip` by compressing file using `.gz` format, removing source file by default (use `--keep` to preserve). If zlib is not supported, triggers an error. 75- `xz` : if lzma support is enabled, will mimic `xz` by compressing file using `.xz` format, removing source file by default (use `--keep` to preserve). If xz is not supported, triggers an error. 76- `lzma` : if lzma support is enabled, will mimic `lzma` by compressing file using `.lzma` format, removing source file by default (use `--keep` to preserve). If lzma is not supported, triggers an error. 77- `lz4` : if lz4 support is enabled, will mimic `lz4` by compressing file using `.lz4` format. If lz4 is not supported, triggers an error. 78- `unzstd` and `unlz4` will decompress any of the supported format. 79- `ungz`, `unxz` and `unlzma` will do the same, and will also remove source file by default (use `--keep` to preserve). 80 81 82#### Dictionary builder in Command Line Interface 83Zstd offers a training mode, which can be used to tune the algorithm for a selected 84type of data, by providing it with a few samples. The result of the training is stored 85in a file selected with the `-o` option (default name is `dictionary`), 86which can be loaded before compression and decompression. 87 88Using a dictionary, the compression ratio achievable on small data improves dramatically. 89These compression gains are achieved while simultaneously providing faster compression and decompression speeds. 90Dictionary work if there is some correlation in a family of small data (there is no universal dictionary). 91Hence, deploying one dictionary per type of data will provide the greater benefits. 92Dictionary gains are mostly effective in the first few KB. Then, the compression algorithm 93will rely more and more on previously decoded content to compress the rest of the file. 94 95Usage of the dictionary builder and created dictionaries with CLI: 96 971. Create the dictionary : `zstd --train PathToTrainingSet/* -o dictionaryName` 982. Compress with the dictionary: `zstd FILE -D dictionaryName` 993. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName` 100 101 102#### Benchmark in Command Line Interface 103CLI includes in-memory compression benchmark module for zstd. 104The benchmark is conducted using given filenames. The files are read into memory and joined together. 105It makes benchmark more precise as it eliminates I/O overhead. 106Multiple filenames can be supplied, as multiple parameters, with wildcards, 107or names of directories can be used as parameters with `-r` option. 108 109The benchmark measures ratio, compressed size, compression and decompression speed. 110One can select compression levels starting from `-b` and ending with `-e`. 111The `-i` parameter selects minimal time used for each of tested levels. 112 113 114#### Usage of Command Line Interface 115The full list of options can be obtained with `-h` or `-H` parameter: 116``` 117Usage : 118 zstd [args] [FILE(s)] [-o file] 119 120FILE : a filename 121 with no FILE, or when FILE is - , read standard input 122Arguments : 123 -# : # compression level (1-19, default: 3) 124 -d : decompression 125 -D file: use `file` as Dictionary 126 -o file: result stored into `file` (only if 1 input file) 127 -f : overwrite output without prompting and (de)compress links 128--rm : remove source file(s) after successful de/compression 129 -k : preserve source file(s) (default) 130 -h/-H : display help/long help and exit 131 132Advanced arguments : 133 -V : display Version number and exit 134 -v : verbose mode; specify multiple times to increase verbosity 135 -q : suppress warnings; specify twice to suppress errors too 136 -c : force write to standard output, even if it is the console 137 -l : print information about zstd compressed files 138--ultra : enable levels beyond 19, up to 22 (requires more memory) 139--long : enable long distance matching (requires more memory) 140--no-dictID : don't write dictID into header (dictionary compression) 141--[no-]check : integrity check (default: enabled) 142 -r : operate recursively on directories 143--format=gzip : compress files to the .gz format 144--format=xz : compress files to the .xz format 145--format=lzma : compress files to the .lzma format 146--test : test compressed file integrity 147--[no-]sparse : sparse mode (default: disabled) 148 -M# : Set a memory usage limit for decompression 149-- : All arguments after "--" are treated as files 150 151Dictionary builder : 152--train ## : create a dictionary from a training set of files 153--train-cover[=k=#,d=#,steps=#] : use the cover algorithm with optional args 154--train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9) 155 -o file : `file` is dictionary name (default: dictionary) 156--maxdict=# : limit dictionary to specified size (default: 112640) 157--dictID=# : force dictionary ID to specified value (default: random) 158 159Benchmark arguments : 160 -b# : benchmark file(s), using # compression level (default: 3) 161 -e# : test all compression levels from -bX to # (default: 1) 162 -i# : minimum evaluation time in seconds (default: 3s) 163 -B# : cut file into independent blocks of size # (default: no block) 164--priority=rt : set process priority to real-time 165``` 166 167 168#### Long distance matching mode 169The long distance matching mode, enabled with `--long`, is designed to improve 170the compression ratio for files with long matches at a large distance (up to the 171maximum window size, `128 MiB`) while still maintaining compression speed. 172 173Enabling this mode sets the window size to `128 MiB` and thus increases the memory 174usage for both the compressor and decompressor. Performance in terms of speed is 175dependent on long matches being found. Compression speed may degrade if few long 176matches are found. Decompression speed usually improves when there are many long 177distance matches. 178 179Below are graphs comparing the compression speed, compression ratio, and 180decompression speed with and without long distance matching on an ideal use 181case: a tar of four versions of clang (versions `3.4.1`, `3.4.2`, `3.5.0`, 182`3.5.1`) with a total size of `244889600 B`. This is an ideal use case as there 183are many long distance matches within the maximum window size of `128 MiB` (each 184version is less than `128 MiB`). 185 186Compression Speed vs Ratio | Decompression Speed 187---------------------------|--------------------- 188 |  189 190| Method | Compression ratio | Compression speed | Decompression speed | 191|:-------|------------------:|-------------------------:|---------------------------:| 192| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` | 193| `zstd -5` | `5.826` | `124.9 MB/s` | `674.0 MB/s` | 194| `zstd -10` | `6.504` | `29.5 MB/s` | `771.3 MB/s` | 195| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` | 196| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s`| 197| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s`| 198 199On this file, the compression ratio improves significantly with minimal impact 200on compression speed, and the decompression speed doubles. 201 202On the other extreme, compressing a file with few long distance matches (such as 203the [Silesia compression corpus]) will likely lead to a deterioration in 204compression speed (for lower levels) with minimal change in compression ratio. 205 206The below table illustrates this on the [Silesia compression corpus]. 207 208[Silesia compression corpus]: http://sun.aei.polsl.pl/~sdeor/index.php?page=silesia 209 210| Method | Compression ratio | Compression speed | Decompression speed | 211|:-------|------------------:|-------------------------:|---------------------------:| 212| `zstd -1` | `2.878` | `231.7 MB/s` | `594.4 MB/s` | 213| `zstd -1 --long` | `2.929` | `106.5 MB/s` | `517.9 MB/s` | 214| `zstd -5` | `3.274` | `77.1 MB/s` | `464.2 MB/s` | 215| `zstd -5 --long` | `3.319` | `51.7 MB/s` | `371.9 MB/s` | 216| `zstd -10` | `3.523` | `16.4 MB/s` | `489.2 MB/s` | 217| `zstd -10 --long`| `3.566` | `16.2 MB/s` | `415.7 MB/s` | 218
