syntax
Meta-characters
Meta-characters
Meta-characters
The power of regular expressions comes from the
ability to include alternatives and repetitions in the pattern.
These are encoded in the pattern by the use of meta-characters, which do not stand for themselves
but instead are interpreted in some special way.
There are two different sets of meta-characters:
those that are recognized anywhere in the pattern except within
square brackets, and those that are recognized in square brackets.
Outside square brackets, the meta-characters are as follows:
| Meta-character | Description |
|---|---|
| \ | general escape character with several uses |
| ^ | assert start of subject (or line, in multiline mode) |
| $ | assert end of subject or before a terminating newline (or end of line, in multiline mode) |
| . | match any character except newline (by default) |
| [ | start character class definition |
| ] | end character class definition |
| | | start of alternative branch |
| ( | start subpattern |
| ) | end subpattern |
| ? | extends the meaning of (, also 0 or 1 quantifier, also makes greedy quantifiers lazy (see repetition) |
| * | 0 or more quantifier |
| + | 1 or more quantifier |
| { | start min/max quantifier |
| } | end min/max quantifier |
Part of a pattern that is in square brackets is called a character
class. In a character class the only meta-characters are:
| Meta-character | Description |
|---|---|
| \ | general escape character |
| ^ | negate the class, but only if the first character |
| – | indicates character range |
The following sections describe the use of each of the
meta-characters.