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-
-Introduction to the lzma command line tool
-------------------------------------------
-
-Overview
-
- The lzma command line tool is similar to gzip and bzip2, but for
- compressing and uncompressing .lzma files.
-
-
-Supported file formats
-
- By default, the tool creates files in the new .lzma format. This can
- be overriden with --format=FMT command line option. Use --format=alone
- to create files in the old LZMA_Alone format.
-
- By default, the tool uncompresses both the new .lzma format and
- LZMA_Alone format. This is to make it transparent to switch from
- the old LZMA_Alone format to the new .lzma format. Since both
- formats use the same filename suffix, average user should never
- notice which format was used.
-
-
-Differences to gzip and bzip2
-
- Standard input and output
-
- Both gzip and bzip2 refuse to write compressed data to a terminal and
- read compressed data from a terminal. With gzip (but not with bzip2),
- this can be overriden with the `--force' option. lzma follows the
- behavior of gzip here.
-
- Usage of LZMA_OPT environment variable
-
- gzip and bzip2 read GZIP and BZIP2 environment variables at startup.
- These variables may contain extra command line options.
-
- gzip and bzip2 allow passing not only options, but also end-of-options
- indicator (`--') and filenames via the environment variable. No quoting
- is supported with the filenames.
-
- Here are examples with gzip. bzip2 behaves identically.
-
- bash$ echo asdf > 'foo bar'
- bash$ GZIP='"foo bar"' gzip
- gzip: "foo: No such file or directory
- gzip: bar": No such file or directory
-
- bash$ GZIP=-- gzip --help
- gzip: --help: No such file or directory
-
- lzma silently ignores all non-option arguments given via the
- environment variable LZMA_OPT. Like on the command line, everything
- after `--' is taken as non-options, and thus ignored in LZMA_OPT.
-
- bash$ LZMA_OPT='--help' lzma --version # Displays help
- bash$ LZMA_OPT='-- --help' lzma --version # Displays version
-
-
-Filter chain presets
-
- Like in gzip and bzip2, lzma supports numbered presets from 1 to 9
- where 1 is the fastest and 9 the best compression. 1 and 2 are for
- fast compressing with small memory usage, 3 to 6 for good compression
- ratio with medium memory usage, and 7 to 9 for excellent compression
- ratio with higher memory requirements. The default is 7 if memory
- usage limit allows.
-
- In future, there will probably be an option like --preset=NAME, which
- will contain more special presets for specific file types.
-
- It's also possible that there will be some heuristics to select good
- filters. For example, the tool could detect when a .tar archive is
- being compressed, and enable x86 filter only for those files in the
- .tar archive that are ELF or PE executables for x86.
-
-
-Specifying custom filter chains
-
- Custom filter chains are specified by using long options with the name
- of the filters in correct order. For example, to pass the input data to
- the x86 filter and the output of that to the LZMA filter, the following
- command will do:
-
- lzma --x86 --lzma filename
-
- Some filters accept options, which are specified as a comma-separated
- list of key=value pairs:
-
- lzma --delta=distance=4 --lzma=dict=4Mi,lc=8,lp=2 filename
-
-
-Memory usage control
-
- By default, the command line tool limits memory usage to 1/3 of the
- available physical RAM. If no preset or custom filter chain has been
- given, the default preset will be used. If the memory limit is too
- low for the default preset, the tool will silently switch to lower
- preset.
-
- When a preset or a custom filter chain has been specified and the
- memory limit is too low, an error message is displayed and no files
- are processed.
-
- If the decoder hits the memory usage limit, an error is displayed and
- no more files are processed.
-