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Brace Expansion

"Brace expansion" is a mechanism by which arbitrary strings may be generated. This mechanism is similar to pathname expansion\fP, but the filenames generated need not exist. Patterns to be brace expanded take the form of an optional .IR preamble , followed by a series of comma-separated strings between a pair of braces, followed by an optional .IR postscript . The preamble is prefixed to each string contained within the braces, and the postscript is then appended to each resulting string, expanding left to right.

Brace expansions may be nested. The results of each expanded string are not sorted; left to right order is preserved. For example, a{\fPd,c,b}\fPe expands into `ade ace abe'.

Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text between the braces.

A correctly-formed brace expansion must contain unquoted opening and closing braces, and at least one unquoted comma. Any incorrectly formed brace expansion is left unchanged. A {\fP or ,\fP may be quoted with a backslash to prevent its being considered part of a brace expression. To avoid conflicts with parameter expansion, the string ${\fP is not considered eligible for brace expansion.

This construct is typically used as shorthand when the common prefix of the strings to be generated is longer than in the above example:

mkdir /usr/local/src/bash/{old,new,dist,bugs} or chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
Brace expansion introduces a slight incompatibility with historical versions of .BR sh . sh does not treat opening or closing braces specially when they appear as part of a word, and preserves them in the output. Bash removes braces from words as a consequence of brace expansion. For example, a word entered to sh as file{1,2}\fP appears identically in the output. The same word is output as file1 file2 after expansion by .BR bash . If strict compatibility with sh is desired, start bash with the +B option or disable brace expansion with the +B option to the set command (see .SM SHELL BUILTIN COMMANDS below).

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