| Character classes |
| . |
any character except newline |
| \w \d \s |
word, digit, whitespace |
| \W \D \S |
not word, digit, whitespace |
| [abc] |
any of a, b, or c |
| [^abc] |
not a, b, or c |
| [a-g] |
character between a & g |
| Anchors |
| ^abc$ |
start / end of the string |
| \b |
word boundary |
| Escaped characters |
| \. \* \\ |
escaped special characters |
| \t \n \r |
tab, linefeed, carriage return |
| \u00A9 |
unicode escaped © |
| Groups & Lookaround |
| (abc) |
capture group |
| \1 |
backreference to group #1 |
| (?:abc) |
non-capturing group |
| (?=abc) |
positive lookahead |
| (?!abc) |
negative lookahead |
| Quantifiers & Alternation |
| a* a+ a? |
0 or more, 1 or more, 0 or 1 |
| a{5} a{2,} |
exactly five, two or more |
| a{1,3} |
between one & three |
| a+? a{2,}? |
match as few as possible |
| ab|cd |
match ab or cd |