bold _italics
| Character | Example | Definition |
|---|---|---|
| * | ab | Matches the previous character 0 or more times |
| + | a+b+ | Matches the previous character 1 or more times |
| [ ] | [a-z] | Matches any character from a to z |
| [^ ]] | [a-z] | Does not matches any character from a to z |
| () | (ab) | A grouped subexpression, this are executed first |
| | | (foo | foot)s |
| {m,n} | a{2,3} | Matches the preceding character, m to n |
| . | b.d | Matches any charater |
| ^ | ^a | Indicates an expression at the begining of the sting |
| \ | ^ |\ | An escape charater |
| $ | [A-Z]*$ | Often at the of the expression it matches the end of the string |
| ?! | ^((?![A-Z]).)*$ | Does seomthing?? expand |
| ? | (swimming )? pool | makes the previous expression optional |
| ?? | (swimming )? pool | lazy |
| (?=) | A(?=B) | look ahead Matches an A followed by a B: AB, ABC, |
| (?!) | A(?!B) | look ahead negaticefind a expression A where B *does not * follows |
| (?<=) | (?<=B)A | look behind Find Expresion A where B preceds it |
| (?<!) | (?<!B)A | look behind negatice find expression A where expression B does not precced |
| (?>) | (?>foo | foot)s |