Documentation / Regular Expressions / The elements of regular expressions
The elements of regular expressions
Character lists [a-z] and classes \s
A character list matches one character in the specified range:
| [a-z] | Any English letter (from a to z) |
| [aeiouy] | Any English vowel |
| [^aeiouy ] | Not vowel and not space |
| [0-9a-f] | A hexadecimal digit (from 0 to 9, or from A to F) |
A character class matches one character of the specified type (letter, digit, etc.):
| \d | A digit |
| \s | Space, tab or line separator |
| \w | A letter |
Dot (.) matches any character.
Repetitions * + ?
The star * matches the previous element zero or more time, the plus + matches it one or more times, and ? matches it zero or one times.
| 0* | None or several zeros |
| \w+ | A word (one or more letters) |
| (http://)? | Optional http:// string |
Anchors ^ and $
Caret ^ matches at the beginning of the line, dollar sign $ matches at the end of the line:
| ^[0-9] | Digit at the beginning of a line |
| \\$ | Backslash at the end of a line |
Alternative |
| (http|ftp|https):// | Any of the these protocols: http:// or ftp:// or https:// |
Backreferences \1
Parentheses mark subexpressions, which are numbered from left to right. You can refer to previously defined subexpressions with \1, \2, etc. syntax:
| (\d+) \1 | Find two equal numbers with space between them (e.g., 123 123) |
Text and metacharacters
If you want to search for a word or a number, you could enter them as is. For example, to search for cocoa, just type this word.
The metacharacters are:
[ ] * + ? { } . ( ) ^ $ | \
If you want to find one of metacharacters, type \ before it. For example, to find the text $100, use \$100. If you want to find the backslash itself, repeat it: \\.