Regular Expression
Regular expression
“A regular expression, regex or regexp (sometimes called a rational expression) is a sequence of characters that define a search pattern.”
| Metacharacter | Description |
|---|---|
| ^ | Matches the starting position within the string. |
| . | Matches any single character. |
| [ ] | Matches a single character that is contained within the brackets. For example, [0-9] specifies a range which matches any digits from 0 to 9. See character classes. |
| [^ ] | Matches a single character that is not contained within the brackets. |
| $ | Matches the ending position of the string. |
| ( ) | Matches a marked subexpression. |
| * | Matches the preceding element zero or more times. |
| ? | Matches the preceding element zero or one time. |
| + | Matches the preceding element one or more times. |
| {n} | Matches the preceding element exactly n times. |
| {min,} | Matches the preceding element at least min times. |
| {min,max} | Matches the preceding element at least min and not more than max times. |
| | | The choice operator matches either the expression before or the expression after the operator. |
Examples
Numeral
[+-]?(\d+(\.\d+)?|\.\d+)([eE][+-]?\d+)?
Analysis
Sign [+-]?
Base (\d+(\.\d+)?|\.\d+)
Exponent ([eE][+-]?\d+)?
Same as [0-9], \d matches any digit. See character classes.
Time
([0-1][0-9]|2[0-3])(:[0-5][0-9](:[0-5][0-9])?)?