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A regular expression is a character sequence that is an abbreviated definition of a set of strings. A string matches a regular expression if it is a member of the set described by the regular expression.
A regular expression is allowed to match anywhere within a string, unless the regular expression is explicitly anchored to the beginning (operator ^) or end (operator $) of the string.
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The following character sequences are recognized:
. matches any single character except newline* (postfix) matches the previous expression zero, one or several times+ (postfix) matches the previous expression one or several times
[+] matches a "+" character (escape mechanism)
? (postfix) matches the previous expression once or not at all[ ] is a character set
- ranges are denoted with a hyphen "
-", as in [a-z]
- an initial caret "
^", as in [^0-9], complements the set (i.e. any character, except a lowercase letter from a to z, is accepted)
[[] matches a "[" character (escape mechanism)
[]] matches a "]" character (escape mechanism)
^ matches at beginning of line$ matches at end of line| (infix) alternative between two expressions( ) grouping of the enclosed expression
[(] matches a "(" character (escape mechanism)
[)] matches a ")" character (escape mechanism)
\ escapes special characters (i.e. ^.[$|*?{'):
\n matches a newline character\. matches a dot "." character\' matches a quote "'" character-
\ cannot be escaped; to search for a backslash, use . to match any single character
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Introduction
