Regular Expressions

Each character matches itself, unless it is one of the special characters + ? . * ^ $ ( ) [ ] { } | \. The special meaning of these characters can be escaped using a \.

• .
• Matches an arbitrary character, but not a newline unless it is a single-line match (see m/ /s).
• (...)
• Groups a series of pattern elements to a single element.
• ^
• Matches the beginning of the target. In multiline mode (see m//m) also matches after every newline character.
• $
• Matches the end of the line. In multiline mode also matches before every newline character.
• [...]
• Denotes a class of characters to match. [^\*(EL] negates the class.
• (... | ... | ...)
• Matches one of the alternatives.
• (?# text)
• Comment.
• (?: regexp)
• Like (regexp) but does not make back-references.
• (?= regexp)
• Zero width positive look-ahead assertion.
• (?! regexp)
• Zero width negative look-ahead assertion.
• (? modifier)
• Embedded pattern-match modifier. modifier can be one or more of i, m, s, or x.

Quantified subpatterns match as many times as possible. When followed with a ? they match the minimum number of times. These are the quantifiers:

• +
• Matches the preceding pattern element one or more times.
• ?
• Matches zero or one times.
• *
• Matches zero or more times.
• {n,m}
• Denotes the minimum n and maximum m match count. {n} means exactly n times; {n,} means at least n times.

A \ escapes any special meaning of the following character if non-alphanumeric, but it turns most alphanumeric characters into something special:

• \w
• Matches alphanumeric, including _, \W matches non-alphanumeric.
• \s
• Matches whitespace, \S matches non-whitespace.
• \d
• Matches numeric, \D matches non-numeric.
• \A
• Matches the beginning of the string, \Z matches the end.
• \b
• Matches word boundaries, \B matches non-boundaries.
• \G
• Matches where the previous m/ /g search left off.
• \n, \r, \f, \t, etc.
• Have their usual meaning.
• \w, \s, and \d
• May be used within character classes, \b denotes a backspace in this context.

Back-references:

• \1...\9
• Refer to matched subexpressions, grouped with ( ), inside the match.
• \10 and up
• Can also be used if the pattern matches that many subexpressions.

See also $1...$9, $+, $&, $`, and $' in the section called "Special Variables".

With modifier x, whitespace can be used in the patterns for readability purposes.