The supported meta characters are:
| . | Match any character but newline. |
| \ | Quote the next metacharacter. |
| ^ | Match the beginning of the line. |
| $ | Match the end of the line (or before newline at the end). |
| | | Alternation. |
| () | Grouping. |
| [] | Character class. |
The following standard escapes are recognized:
| \a | Bell. |
| \e | Escape. |
| \f | Form-feed. |
| \n | Newline. |
| \r | Carriage-return. |
| \t | Tab. |
The following Perl-defined zero-width assertions are supported:
| \A | Match only at beginning of string. |
| \b | Match a word boundary. |
| \B | Match a non-word boundary. |
| \z | Match only at end of string. |
| \Z | Match only at end of string, or before newline at the end. |
The following standard character classes are recognized:
| \d | Digit. |
| \D | Non-digit. |
| \s | Whitespace. |
| \S | Non-whitespace. |
| \w | Word: [A-Za-z0-9_]. |
| \W | Non-word. |
The following standard quantifiers are recognized:
| * | Match 0 or more times. |
| + | Match 1 or more times. |
| ? | Match 1 or 0 times. |
| { n } | Match exactly n times. |
| { n,} | Match at least n times. |
| { n, m } | Match at least n but not more than m times. |
Back References
Back-references like \1 match whatever the corresponding group (parenthesized regular expression component) matched. For example the regular expression
./^(.+)\1$/
matches repeated strings like
xyzxyz
abab
Allen’s comments also document support for:
| \033 | Octal char. |
| \x1B | Hex char. |
| \x { 263a } | Wide hex char. (Unicode SMILEY) |
| \c[ | Control char. |
| \L | Lowercase until \E. (Think vi.) |
| \U | Uppercase until \E. (Think vi.) |
| \E | End case modification. (Think vi.) |
| \Q | Quote (disable) pattern metacharacters until next \E. |
| \pP | Match P, named property. Use \p { Prop } for longer names. |
| \PP | Match non-P. |
| \C | Match a single C char (octet) even under utf8. |
Code comments document the following as implemented by the parser but not by the regular expression engine proper:
| \N { name } | Named char. |
| \l | Lowercase next char. (Think vi.) |
| \u | Uppercase next char. (Think vi.) |
There is currently no locale support — feel free to contribute this!