| ^ | Beginning of a string |
| $ | End of a string |
| . | Match any character (except newline) when used outside of a character set |
| * | Match 0 or more times |
| + | Match 1 or more times |
| ? | Match 0 or 1 times |
| | | Alternation |
| ( ) | Grouping; "storing" |
| [ ] | Character set |
| { } | Repetition modifier |
| \ | Quote or special |
| Note | To present a metacharacter as a data character standing for itself, precede it with a backslash '\'.
For example, \. will match the full stop character '.' |
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Repetitions
| a* | 0 or more 'a' |
| a+ | 1 or more 'a' |
| a? | 0 or 1 'a' (i.e., optional 'a') |
| a{m} | exactly m 'a' |
| a{m, } | at least m 'a' |
| a{m, n} | at least m but at most n 'a' |
| expr? | shortest match taken from the repetition expression expr (i.e., a*?) |
| Note | By default it will find the longest match. Use the expr? to find the shortest match. |
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Single characters
| \t | tab |
| \n | newline |
| \r | return (CR) |
| \xhh | character with hexadecimal code hh |
Zero-width assertions
| \b | "word" boundary |
| \B | not a "word" boundary |
Matching
| \w | matches any single character classified as a "word" character (alphanumeric or '_') |
| \W | matches any non-"word" character |
| \s | matches any whitespace character (space, tab, newline) |
| \S | matches any non-whitespace character |
| \d | matches any digit character (equivalent to [0-9]) |
| \D | matches any non-digit character |
Character sets
| [characters] | Matches any of the characters in the sequence |
| [x-y] | Matches any of the characters from x to y (inclusively) |
| [\-] | Matches the hyphen character '-' |
| [\n] | Matches the newline character |
| [^expr] | Matches any characters except those specified in the expression expr |
| Note | Other single character denotations with the backslash '\' apply normally too. |
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Character and equivalence classes
Character and equivalence classes can only be used in Character sets and use the following syntax:
| [:class:] | Will match any characters from the specified class
Where class can be any of the character class names |
| [=name=] | Will match the base character from the specified character or symbolic name.
Where name can be any character or it's symbolic name |
| Note | A base character is a character that ignores case, any accents or unique regional tailoring. |
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| Example | [[:digit:]] will match any digit character.
[[=a=]] will match a, à, á, â, ã, ä, å, A, À, Á, Â, Ã, Ä and Å. |
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Operator precedence
| 1 | [==] [::] | Collation-related bracket symbols |
| 2 | \ | Escaped characters |
| 3 | [ ] | Character set (bracket expression) |
| 4 | ( ) | Grouping |
| 5 | * + ? {m,n} | Repetitions |
| 6 | | Concatenation |
| 7 | ^ $ | Anchoring |
| 8 | | | Alternation |
