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diff --git a/programs/zstd.1.md b/programs/zstd.1.md index 3ab2667a0483e..e3daa4c87ac7f 100644 --- a/programs/zstd.1.md +++ b/programs/zstd.1.md @@ -144,6 +144,18 @@ the last one takes effect. Due to the chaotic nature of dynamic adaptation, compressed result is not reproducible. _note_ : at the time of this writing, `--adapt` can remain stuck at low speed when combined with multiple worker threads (>=2). +* `--stream-size=#` : + Sets the pledged source size of input coming from a stream. This value must be exact, as it + will be included in the produced frame header. Incorrect stream sizes will cause an error. + This information will be used to better optimize compression parameters, resulting in + better and potentially faster compression, especially for smaller source sizes. +* `--size-hint=#`: + When handling input from a stream, `zstd` must guess how large the source size + will be when optimizing compression parameters. If the stream size is relatively + small, this guess may be a poor one, resulting in a higher compression ratio than + expected. This feature allows for controlling the guess when needed. + Exact guesses result in better compression ratios. Overestimates result in slightly + degraded compression ratios, while underestimates may result in significant degradation. * `--rsyncable` : `zstd` will periodically synchronize the compression state to make the compressed file more rsync-friendly. There is a negligible impact to @@ -179,6 +191,13 @@ the last one takes effect. This is the default behavior. * `-r`: operate recursively on directories +* `--output-dir-flat[=dir]`: + resulting files are stored into target `dir` directory, + instead of same directory as origin file. + Be aware that this command can introduce name collision issues, + if multiple files, from different directories, end up having the same name. + Collision resolution ensures first file with a given name will be present in `dir`, + while in combination with `-f`, the last file will be present instead. * `--format=FORMAT`: compress and decompress in other formats. If compiled with support, zstd can compress to or decompress from other compression algorithm @@ -202,6 +221,16 @@ the last one takes effect. * `--`: All arguments after `--` are treated as files +### Restricted usage of Environment Variables + +Using environment variables to set parameters has security implications. +Therefore, this avenue is intentionally restricted. +Only `ZSTD_CLEVEL` is supported currently, for setting compression level. +`ZSTD_CLEVEL` can be used to set the level between 1 and 19 (the "normal" range). +If the value of `ZSTD_CLEVEL` is not a valid integer, it will be ignored with a warning message. +`ZSTD_CLEVEL` just replaces the default compression level (`3`). +It can be overridden by corresponding command line arguments. + DICTIONARY BUILDER ------------------ |