Perl5 regular expressions

Here we summarize the syntax of Perl5.003 regular expressions, all of which is supported by the Perl5 classes in this package. However, for a definitive reference, you should consult the perlre man page that accompanies the Perl5 distribution and also the book Programming Perl, 2nd Edition from O'Reilly & Associates. We are working toward implementing the features added after Perl5.003 up to and including Perl 5.6. Please remember, we only guarantee support for Perl5.003 expressions in version 2.0.

By default, a quantified subpattern is greedy . In other words it matches as many times as possible without causing the rest of the pattern not to match. To change the quantifiers to match the minimum number of times possible, without causing the rest of the pattern not to match, you may use a "?" right after the quantifier.

Match 0 or more times
Match 1 or more times
Match 0 or 1 time
Match exactly n times
Match at least n times
Match at least n but not more than m times

Perl5 extended regular expressions are fully supported.

An embedded comment causing text to be ignored.
Groups things like "()" but doesn't cause the group match to be saved.
A zero-width positive lookahead assertion. For example, \w+(?=\s) matches a word followed by whitespace, without including whitespace in the MatchResult.
A zero-width negative lookahead assertion. For example foo(?!bar) matches any occurrence of "foo" that isn't followed by "bar". Remember that this is a zero-width assertion, which means that a(?!b)d will match ad because a is followed by a character that is not b (the d) and a d follows the zero-width assertion.
One or more embedded pattern-match modifiers. i enables case insensitivity, m enables multiline treatment of the input, s enables single line treatment of the input, and x enables extended whitespace comments.

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