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51 lines
2.6 KiB
Plaintext
51 lines
2.6 KiB
Plaintext
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Brace Expansion
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Brace expansion is a mechanism by which arbitrary strings may be gener-
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ated. This mechanism is similar to pathname expansion, but the file-
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names generated need not exist. Patterns to be brace expanded take the
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form of an optional preamble, followed by either a series of comma-sep-
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arated strings or a sequence expression between a pair of braces, fol-
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lowed by an optional postscript. The preamble is prefixed to each
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string contained within the braces, and the postscript is then appended
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to each resulting string, expanding left to right.
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Brace expansions may be nested. The results of each expanded string
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are not sorted; left to right order is preserved. For example,
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a{d,c,b}e expands into `ade ace abe'.
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A sequence expression takes the form {x..y}, where x and y are either
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integers or single characters. When integers are supplied, the expres-
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sion expands to each number between x and y, inclusive. When charac-
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ters are supplied, the expression expands to each character lexico-
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graphically between x and y, inclusive. Note that both x and y must be
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of the same type.
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Brace expansion is performed before any other expansions, and any char-
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acters special to other expansions are preserved in the result. It is
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strictly textual. Bash does not apply any syntactic interpretation to
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the context of the expansion or the text between the braces.
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A correctly-formed brace expansion must contain unquoted opening and
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closing braces, and at least one unquoted comma or a valid sequence
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expression. Any incorrectly formed brace expansion is left unchanged.
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A { or , may be quoted with a backslash to prevent its being considered
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part of a brace expression. To avoid conflicts with parameter expan-
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sion, the string ${ is not considered eligible for brace expansion.
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This construct is typically used as shorthand when the common prefix of
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the strings to be generated is longer than in the above example:
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mkdir /usr/local/src/bash/{old,new,dist,bugs}
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or
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chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
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Brace expansion introduces a slight incompatibility with historical
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versions of sh. sh does not treat opening or closing braces specially
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when they appear as part of a word, and preserves them in the output.
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Bash removes braces from words as a consequence of brace expansion.
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For example, a word entered to sh as file{1,2} appears identically in
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the output. The same word is output as file1 file2 after expansion by
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bash. If strict compatibility with sh is desired, start bash with the
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+B option or disable brace expansion with the +B option to the set com-
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mand
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