Bracket expressions are a list of characters and/or character classes enclosed in
brackets []. Use bracket expressions to match single characters in a list, or a range
of
characters in a list. If the first character of the list is the carat ^ then it matches
characters that are not in the list.
For example:
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EXPRESSION
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MATCHES
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[abc]
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a, b, or c
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[a-z]
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a through z
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[^abc]
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Any character except a, b, or c
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[[:alpha:]]
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Any alphabetic character (see below)
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The following character classes must be within a bracket expression or it will be
treated as a common expression.
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CHARACTER CLASS
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DESCRIPTION
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[:alpha:]
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Alphabetic characters
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[:digit:]
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Digits
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[:alnum:]
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Alphabetic characters and numeric characters
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[:cntrl:]
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Control character
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[:blank:]
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Space and tab
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[:space:]
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All white space characters
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[:graph:]
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Non-blank (not spaces, control characters, or the like)
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[:print:]
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Like [:graph:], but includes the space character
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[:punct:]
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Punctuation characters
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[:lower:]
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Lowercase alphabetic character
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[:upper:]
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Uppercase alphabetic character
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[:xdigit:]
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Digits allowed in a hexadecimal number (0-9a-fA-F)
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For example:
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a[[:digit:]]b matches "a0b", "a1b", ..., "a9b".
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a[:digit:]b matches "a:b", "adb", …, "atb".
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[[:digit:]abc] matches any digit or any of "a", "b", and "c".
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[abc[:digit:]] matches any digit or any of "a", "b", and "c".
For a case-insensitive expression, [:lower:] and [:upper:] are equivalent to [:alpha:].