| Anchor | Description | Example | Valid match | Invalid |
|---|---|---|---|---|
| ^ | start of string or line | ^foam | foam is fun | bath foam |
| $ | end of string or line | ish$ | finish | finishing |
| \b | word boundary; position between a word character (\w), and a nonword character (\W) | \bis\b | This island is beautiful | This island isn't beautiful |
| \B | not-word-boundary. | \Bland | island | peninsula |
| Char class | Description | Example | Valid match | Invalid |
|---|---|---|---|---|
| . | match any chars except new line | b.ttle | battle, bottle | bttle |
| [ ] | class definition | [axf] | a, x, f | b |
| [ - ] | class definition range | [a-c] | a, b, c | d |
| [^ ] | Not in class | [^abc] | d, e | a |
| [:class:] | POSIX class | [:alpha:] | string | 0101 |
| \s | white space, [\n\r\f\t ] | good\smorning | good morning | good.morning |
| \S | no-white space, [^\n\r\f\t] | good\Smorning | goodmorning | good morning |
| \d | digit | \d{2} | 23 | 1a |
| \D | non-digit | \D{3} | foo, bar | fo1 |
| \w | word, [a-z-A-Z0-9_] | \w{4} | v411 | v4.1 |
| \W | non word, [^a-z-A-Z0-9_] | .$%? | .$%? | .ab? |
| Sequence | Description | Example | Valid match | Invalid |
|---|---|---|---|---|
| ( ) | subpattern | foot(er|ball) | footer or footbal | footpath |
| (?:...) | subpattern, but does not capture submatch | (?:hello) | hello | hallo |
| + | one or more quantifier | ye+ah | yeah, yeeeah | yah |
| * | zero or more quantifier | ye*ah | yeeah, yeeeah, yah | yeh |
| ? | zero or one quantifier | yes? | yes, ye | yess |
| ?? | zero or one, as few times as possible (lazy) | yea??h | yeah | yeaah |
| +? | one or more lazy | /<.+?>/g |
<P>foo</P> matches only <P> and </P> |
|
| *? | zero or more, lazy | /<.*?>/g |
<html> |
|
| {n} | n times exactly | fo{2} | foo | fooo |
| {n,m} | from n to m times | go{2,3}d | good,goood | gooood |
| Special character | Description |
|---|---|
| |general escape | |
| \n | new line |
| \r | carriage return |
| \t | tab |
| \f | form feed |
| [\b] | backspace |
| Assertion | Description | Example | Valid match | Invalid |
|---|---|---|---|---|
| (?=...) | positive lookahead | question(?=s) | questions | question |
| (?!...) | negative lookahead | answer(?!s) | answer | answers |
| (?<=...) | positive look-behind | (?<=appl)e | apple | application |
| (?<!...) | negative look-behind | (?<!goo)d | mood | good |
| Pattern modifier | Description |
|---|---|
| g | global match |
| i | case-insensitiv, match both uppercase and lowercase |
| m | multiple lines |
| s | single line (by default) |
| x | ingore whitespace allows comments |
| A | anchored, the pattern is forced to ^ |
| D | dollar end only, a dollar metacharacter matches only at the end |
| S | extra analysis performed, useful for non-anchored patterns |
| U | ungreedy, greedy patterns becomes lazy by default |
| X | additional functionality of PCRE (PCRE extra) |
| J | allow duplicate names for subpatterns |
| u | unicode, pattern and subject strings are treated as UTF-8 |