A Primer on Regex
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This page is part of a primer series that also includes Java, Python, JavaScript (JS), and TypeScript. It is subject to continuous improvement.
Character Classes
| Pattern | Description (matches...) |
|---|---|
| [abcde] | any of a, b, c, d, and e |
| [^abcde] | all but any of a, b, c, d, and e (^ means negation) |
| [a-e] | any character in the reange, a-e |
| [a-e[w-z]] | any character in the range, a-e or w-z (union) |
| [a-e&&[c-e]] | only common characters in both ranges: c-e (intersection) |
| [a-e&&[^c-e]] | any character in the range a-e, but not in the range c-e: a-b (subtraction) |
| . | any character |
| \d | any digit; equivalent to [0-9] |
| \D | any character that is not a digit: equivalent to [^0-9] |
| \s | a space character |
| \S | any character that is not a space character: equivalent to [^\s] |
| \w | a word character (alphanumeric/underscore): equivalent to [a-zA-Z0-9_] |
| \W | any character that is not a word character: equivalent to [^\w] |
Boundary Patterns
| Pattern | Description (matches...) |
|---|---|
| ^ | the beginning of a line |
| $ | the end of a line |
| \A | the beginning of the input |
| \b | the word boundary line |
| \B | the non-word boundary |
| \G | the end of the previous match |
| \z | the end of the input |
| \Z | the end of the input (if present, for the final terminator) |
Quantifiers
- Curly braces, {}, or symbols like *, ?, + are used to quantify the number of occurrences of a pattern.
- Options include: {specific number}, {minimum number, maximum number}, and {minimum number,}
- * : {0,} (used to search for patterns that may occur any number of times, or may not be present)
- ? : {0,1} (used to search for patterns that may or may not be present)
- + : {1,} (used to search for patterns that may occur at least once or more times)
- Useful external link 1: Quantifiers
- Useful external link 2: Symbols
- Useful external link 3: More symbols
Logical Operators
| Pattern | Description (matches...) |
|---|---|
| x|y | x or y |
| xy | First x, then y |
Groups
- Defined using (pattern)
| Pattern | Description (matches...) |
|---|---|
| (\w\d\w) | a group having a digit character in the middle of two word characters |
Backreferences
- Added by putting \n at the end of a pattern where n is the group number
| Pattern | Description (matches...) |
|---|---|
| (\w\d\w)/\1 | a group—having a digit character in the middle of 2 word characters—repeated twice |