(bash.info) Brace Expansion
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3.5.1 Brace Expansion
---------------------
Brace expansion is a mechanism by which arbitrary strings may be
generated. This mechanism is similar to FILENAME EXPANSION (
Filename Expansion), but the filenames generated need not exist.
Patterns to be brace expanded take the form of an optional PREAMBLE,
followed by either a series of comma-separated strings or a sequence
expression between a pair of braces, followed by an optional 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,
bash$ echo a{d,c,b}e
ade ace abe
A sequence expression takes the form `{X..Y[..INCR]}', where X and Y
are either integers or single characters, and INCR, an optional
increment, is an integer. When integers are supplied, the expression
expands to each number between X and Y, inclusive. Supplied integers
may be prefixed with `0' to force each term to have the same width.
When either X or Y begins with a zero, the shell attempts to force all
generated terms to contain the same number of digits, zero-padding
where necessary. When characters are supplied, the expression expands
to each character lexicographically between X and Y, inclusive, using
the default C locale. Note that both X and Y must be of the same type.
When the increment is supplied, it is used as the difference between
each term. The default increment is 1 or -1 as appropriate.
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. To
avoid conflicts with parameter expansion, the string `${' is not
considered eligible for brace expansion.
A correctly-formed brace expansion must contain unquoted opening and
closing braces, and at least one unquoted comma or a valid sequence
expression. Any incorrectly formed brace expansion is left unchanged.
A { or `,' may be quoted with a backslash to prevent its being
considered part of a brace expression. To avoid conflicts with
parameter expansion, the string `${' 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}}
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