Regular Expression is a powerful text search engine. Here is the quick reference.
Anchors
| ^ | | start of subject |
| $ | | end of subject |
| \b | | word boundary |
| \B | | not a word boundary |
Quantifiers
| ? | | 0 or 1, greedy |
| ?+ | | 0 or 1, possessive |
| ?? | | 0 or 1, lazy |
| * | | 0 or more, greedy |
| *+ | | 0 or more, possessive |
| *? | | 0 or more, lazy |
| + | | 1 or more, greedy |
| ++ | | 1 or more, possessive |
| +? | | 1 or more, lazy |
| {n} | | exactly n |
| {n,m} | | at least n, no more than m, greedy |
| {n,m}+ | | at least n, no more than m, possessive |
| {n,m}? | | at least n, no more than m, lazy |
| {n,} | | n or more, greedy |
| {n,}+ | | n or more, possessive |
| {n,}? | | n or more, lazy |
Escaped Characters
| \n | | newline (hex 0A) |
| \r | | carriage return (hex 0D) |
| \t | | tab (hex 09) |
| \N{U+hh..} | | character with Unicode code point hh.. |
| \xhh | | character with hex code hh |
| \x{hh..} | | character with hex code hh.. |
Character Types
| . | | any character except newline |
| \d | | a decimal digit |
| \D | | a character that is not a decimal digit |
| \h | | a horizontal white space character |
| \H | | a character that is not a horizontal white space character |
| \N | | a character that is not a newline |
| \s | | a white space character |
| \S | | a character that is not a white space character |
| \w | | a “word” character |
| \W | | a “non-word” character |
Character Classes
| […] | | positive character class |
| [^…] | | negative character class |
| [x-y] | | range (can be used for hex characters) |
Capturing
| (…) | | capture group |
| (?<name>…) | | named capture group |
| (?:…) | | non-capture group |
Lookahead And Lookbehind
| (?=…) | | positive lookahead |
| (?!…) | | negative lookahead |
| (?<=…) | | positive lookbehind |
| (?<!…) | | negative lookbehind |
Back References
| \n | | reference by number |
| \k<name> | | reference by name |
