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 supports 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- __ZSTD_NOBENCH__ : `zstd` cli will be compiled without its integrated benchmark module. 65 This can be useful to produce smaller binaries. 66 In this case, the corresponding unit can also be excluded from compilation target. 67 68- __ZSTD_NODICT__ : `zstd` cli will be compiled without support for the integrated dictionary builder. 69 This can be useful to produce smaller binaries. 70 In this case, the corresponding unit can also be excluded from compilation target. 71 72- __ZSTD_NOCOMPRESS__ : `zstd` cli will be compiled without support for compression. 73 The resulting binary will only be able to decompress files. 74 This can be useful to produce smaller binaries. 75 A corresponding `Makefile` target using this ability is `zstd-decompress`. 76 77- __ZSTD_NODECOMPRESS__ : `zstd` cli will be compiled without support for decompression. 78 The resulting binary will only be able to compress files. 79 This can be useful to produce smaller binaries. 80 A corresponding `Makefile` target using this ability is `zstd-compress`. 81 82- __BACKTRACE__ : `zstd` can display a stack backtrace when execution 83 generates a runtime exception. By default, this feature may be 84 degraded/disabled on some platforms unless additional compiler directives are 85 applied. When triaging a runtime issue, enabling this feature can provide 86 more context to determine the location of the fault. 87 Example : `make zstd BACKTRACE=1` 88 89 90### Aggregation of parameters 91CLI supports aggregation of parameters i.e. `-b1`, `-e18`, and `-i1` can be joined into `-b1e18i1`. 92 93 94### Symlink shortcuts 95It's possible to invoke `zstd` through a symlink. 96When the name of the symlink has a specific value, it triggers an associated behavior. 97- `zstdmt` : compress using all cores available on local system. 98- `zcat` : will decompress and output target file using any of the supported formats. `gzcat` and `zstdcat` are also equivalent. 99- `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. 100- `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. 101- `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. 102- `lz4` : if lz4 support is enabled, will mimic `lz4` by compressing file using `.lz4` format. If lz4 is not supported, triggers an error. 103- `unzstd` and `unlz4` will decompress any of the supported format. 104- `ungz`, `unxz` and `unlzma` will do the same, and will also remove source file by default (use `--keep` to preserve). 105 106 107### Dictionary builder in Command Line Interface 108Zstd offers a training mode, which can be used to tune the algorithm for a selected 109type of data, by providing it with a few samples. The result of the training is stored 110in a file selected with the `-o` option (default name is `dictionary`), 111which can be loaded before compression and decompression. 112 113Using a dictionary, the compression ratio achievable on small data improves dramatically. 114These compression gains are achieved while simultaneously providing faster compression and decompression speeds. 115Dictionary work if there is some correlation in a family of small data (there is no universal dictionary). 116Hence, deploying one dictionary per type of data will provide the greater benefits. 117Dictionary gains are mostly effective in the first few KB. Then, the compression algorithm 118will rely more and more on previously decoded content to compress the rest of the file. 119 120Usage of the dictionary builder and created dictionaries with CLI: 121 1221. Create the dictionary : `zstd --train PathToTrainingSet/* -o dictionaryName` 1232. Compress with the dictionary: `zstd FILE -D dictionaryName` 1243. Decompress with the dictionary: `zstd --decompress FILE.zst -D dictionaryName` 125 126 127### Benchmark in Command Line Interface 128CLI includes in-memory compression benchmark module for zstd. 129The benchmark is conducted using given filenames. The files are read into memory and joined together. 130It makes benchmark more precise as it eliminates I/O overhead. 131Multiple filenames can be supplied, as multiple parameters, with wildcards, 132or names of directories can be used as parameters with `-r` option. 133 134The benchmark measures ratio, compressed size, compression and decompression speed. 135One can select compression levels starting from `-b` and ending with `-e`. 136The `-i` parameter selects minimal time used for each of tested levels. 137 138 139### Usage of Command Line Interface 140The full list of options can be obtained with `-h` or `-H` parameter: 141``` 142Usage : 143 zstd [args] [FILE(s)] [-o file] 144 145FILE : a filename 146 with no FILE, or when FILE is - , read standard input 147Arguments : 148 -# : # compression level (1-19, default: 3) 149 -d : decompression 150 -D DICT: use DICT as Dictionary for compression or decompression 151 -o file: result stored into `file` (only 1 output file) 152 -f : overwrite output without prompting, also (de)compress links 153--rm : remove source file(s) after successful de/compression 154 -k : preserve source file(s) (default) 155 -h/-H : display help/long help and exit 156 157Advanced arguments : 158 -V : display Version number and exit 159 -c : write to standard output (even if it is the console) 160 -v : verbose mode; specify multiple times to increase verbosity 161 -q : suppress warnings; specify twice to suppress errors too 162--no-progress : do not display the progress counter 163 -r : operate recursively on directories 164--filelist FILE : read list of files to operate upon from FILE 165--output-dir-flat DIR : processed files are stored into DIR 166--output-dir-mirror DIR : processed files are stored into DIR respecting original directory structure 167--[no-]asyncio : use asynchronous IO (default: enabled) 168--[no-]check : during compression, add XXH64 integrity checksum to frame (default: enabled). If specified with -d, decompressor will ignore/validate checksums in compressed frame (default: validate). 169-- : All arguments after "--" are treated as files 170 171Advanced compression arguments : 172--ultra : enable levels beyond 19, up to 22 (requires more memory) 173--long[=#]: enable long distance matching with given window log (default: 27) 174--fast[=#]: switch to very fast compression levels (default: 1) 175--adapt : dynamically adapt compression level to I/O conditions 176--patch-from=FILE : specify the file to be used as a reference point for zstd's diff engine 177 -T# : spawns # compression threads (default: 1, 0==# cores) 178 -B# : select size of each job (default: 0==automatic) 179--single-thread : use a single thread for both I/O and compression (result slightly different than -T1) 180--rsyncable : compress using a rsync-friendly method (-B sets block size) 181--exclude-compressed: only compress files that are not already compressed 182--stream-size=# : specify size of streaming input from `stdin` 183--size-hint=# optimize compression parameters for streaming input of approximately this size 184--target-compressed-block-size=# : generate compressed block of approximately targeted size 185--no-dictID : don't write dictID into header (dictionary compression only) 186--[no-]compress-literals : force (un)compressed literals 187--format=zstd : compress files to the .zst format (default) 188--format=gzip : compress files to the .gz format 189--format=xz : compress files to the .xz format 190--format=lzma : compress files to the .lzma format 191--format=lz4 : compress files to the .lz4 format 192 193Advanced decompression arguments : 194 -l : print information about zstd compressed files 195--test : test compressed file integrity 196 -M# : Set a memory usage limit for decompression 197--[no-]sparse : sparse mode (default: disabled) 198 199Dictionary builder : 200--train ## : create a dictionary from a training set of files 201--train-cover[=k=#,d=#,steps=#,split=#,shrink[=#]] : use the cover algorithm with optional args 202--train-fastcover[=k=#,d=#,f=#,steps=#,split=#,accel=#,shrink[=#]] : use the fast cover algorithm with optional args 203--train-legacy[=s=#] : use the legacy algorithm with selectivity (default: 9) 204 -o DICT : DICT is dictionary name (default: dictionary) 205--maxdict=# : limit dictionary to specified size (default: 112640) 206--dictID=# : force dictionary ID to specified value (default: random) 207 208Benchmark arguments : 209 -b# : benchmark file(s), using # compression level (default: 3) 210 -e# : test all compression levels successively from -b# to -e# (default: 1) 211 -i# : minimum evaluation time in seconds (default: 3s) 212 -B# : cut file into independent chunks of size # (default: no chunking) 213 -S : output one benchmark result per input file (default: consolidated result) 214--priority=rt : set process priority to real-time 215``` 216 217### Passing parameters through Environment Variables 218There is no "generic" way to pass "any kind of parameter" to `zstd` in a pass-through manner. 219Using environment variables for this purpose has security implications. 220Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL` and `ZSTD_NBTHREADS`. 221 222`ZSTD_CLEVEL` can be used to modify the default compression level of `zstd` 223(usually set to `3`) to another value between 1 and 19 (the "normal" range). 224 225`ZSTD_NBTHREADS` can be used to specify a number of threads 226that `zstd` will use for compression, which by default is `1`. 227This functionality only exists when `zstd` is compiled with multithread support. 228`0` means "use as many threads as detected cpu cores on local system". 229The max # of threads is capped at `ZSTDMT_NBWORKERS_MAX`, 230which is either 64 in 32-bit mode, or 256 for 64-bit environments. 231 232This functionality can be useful when `zstd` CLI is invoked in a way that doesn't allow passing arguments. 233One such scenario is `tar --zstd`. 234As `ZSTD_CLEVEL` and `ZSTD_NBTHREADS` only replace the default compression level 235and number of threads respectively, they can both be overridden by corresponding command line arguments: 236`-#` for compression level and `-T#` for number of threads. 237 238 239### Long distance matching mode 240The long distance matching mode, enabled with `--long`, is designed to improve 241the compression ratio for files with long matches at a large distance (up to the 242maximum window size, `128 MiB`) while still maintaining compression speed. 243 244Enabling this mode sets the window size to `128 MiB` and thus increases the memory 245usage for both the compressor and decompressor. Performance in terms of speed is 246dependent on long matches being found. Compression speed may degrade if few long 247matches are found. Decompression speed usually improves when there are many long 248distance matches. 249 250Below are graphs comparing the compression speed, compression ratio, and 251decompression speed with and without long distance matching on an ideal use 252case: a tar of four versions of clang (versions `3.4.1`, `3.4.2`, `3.5.0`, 253`3.5.1`) with a total size of `244889600 B`. This is an ideal use case as there 254are many long distance matches within the maximum window size of `128 MiB` (each 255version is less than `128 MiB`). 256 257Compression Speed vs Ratio | Decompression Speed 258---------------------------|--------------------- 259 |  260 261| Method | Compression ratio | Compression speed | Decompression speed | 262|:-------|------------------:|-------------------------:|---------------------------:| 263| `zstd -1` | `5.065` | `284.8 MB/s` | `759.3 MB/s` | 264| `zstd -5` | `5.826` | `124.9 MB/s` | `674.0 MB/s` | 265| `zstd -10` | `6.504` | `29.5 MB/s` | `771.3 MB/s` | 266| `zstd -1 --long` | `17.426` | `220.6 MB/s` | `1638.4 MB/s` | 267| `zstd -5 --long` | `19.661` | `165.5 MB/s` | `1530.6 MB/s` | 268| `zstd -10 --long`| `21.949` | `75.6 MB/s` | `1632.6 MB/s` | 269 270On this file, the compression ratio improves significantly with minimal impact 271on compression speed, and the decompression speed doubles. 272 273On the other extreme, compressing a file with few long distance matches (such as 274the [Silesia compression corpus]) will likely lead to a deterioration in 275compression speed (for lower levels) with minimal change in compression ratio. 276 277The below table illustrates this on the [Silesia compression corpus]. 278 279[Silesia compression corpus]: https://sun.aei.polsl.pl//~sdeor/index.php?page=silesia 280 281| Method | Compression ratio | Compression speed | Decompression speed | 282|:-------|------------------:|------------------:|---------------------:| 283| `zstd -1` | `2.878` | `231.7 MB/s` | `594.4 MB/s` | 284| `zstd -1 --long` | `2.929` | `106.5 MB/s` | `517.9 MB/s` | 285| `zstd -5` | `3.274` | `77.1 MB/s` | `464.2 MB/s` | 286| `zstd -5 --long` | `3.319` | `51.7 MB/s` | `371.9 MB/s` | 287| `zstd -10` | `3.523` | `16.4 MB/s` | `489.2 MB/s` | 288| `zstd -10 --long`| `3.566` | `16.2 MB/s` | `415.7 MB/s` | 289 290 291### zstdgrep 292 293`zstdgrep` is a utility which makes it possible to `grep` directly a `.zst` compressed file. 294It's used the same way as normal `grep`, for example : 295`zstdgrep pattern file.zst` 296 297`zstdgrep` is _not_ compatible with dictionary compression. 298 299To search into a file compressed with a dictionary, 300it's necessary to decompress it using `zstd` or `zstdcat`, 301and then pipe the result to `grep`. For example : 302`zstdcat -D dictionary -qc -- file.zst | grep pattern` 303
