Update documentation for environment variable
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@ -204,14 +204,19 @@ Benchmark 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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`ZSTD_NUMTHREADS` can be used to specify number of threads that `zstd` will use during compression, which by default is `1`.
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This functionality only exists when `zstd` is compiled with multithread support.
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The max # of threads is capped at: `ZSTDMT_NBWORKERS_MAX==200`.
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This functionality 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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As `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS` only replace the default compression level
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and number of threads, respectively, they can both be overridden by corresponding command line arguments:
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`-#` for compression level and `-T#` for number of threads.
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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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Therefore, this avenue is intentionally restricted and only supports `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS`.
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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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@ -270,11 +270,20 @@ the last one takes effect.
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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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Only `ZSTD_CLEVEL` and `ZSTD_NUMTHREADS` are currently supported.
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They set the compression level and number of threads to use during compression, respectively.
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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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`ZSTD_NUMTHREADS` can be used to set the number of threads `zstd` will attempt to use during compression.
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If the value of `ZSTD_NUMTHREADS` is not a valid unsigned integer, it will be ignored with a warning message.
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'ZSTD_NUMTHREADS` has a default value of (`1`), and is capped at ZSTDMT_NBWORKERS_MAX==200. `zstd` must be
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compiled with multithread support for this to have any effect.
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They can both be overridden by corresponding command line arguments:
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`-#` for compression level and `-T#` for number of compression threads.
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DICTIONARY BUILDER
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