Regex

Regex

Reference

Syntax

\ Escaping

make a metacharacter represents itself

[] (|) OR operation

match any character inside the []

Except ^

[^a-z] matches any character except lowercase letter a-z
[^a-z0-9] matches any character except lowercase letter a-z and digits

* + {} ? Quantifiers

* zero or more
+ one or more
{} range
? either have it or not

. Wildcard

anything

[a-zA-Z0-9] Range

\d \w \s Character Classes

\d any number
\D anything except for number
\w any alphabet or number
\W anything except for number and alphabets
\s any whitespace: \t tab \r return \n newline vertical tab and form feed character
\S anything except for whitespace

^ $ Anchors

^ line start
$ line end

Add-on

Grouping and Capturing

() group the results that match the criteria between the brackets
(?:expression) non-captured groups
(?<group_name>regular_expression) OR (?'named_group'regular_expression) define explicit names

\b Boundary

\1 \k<name> Back Referencing

\1 for automatic numbered group
\k<name> OR \k'name' for explicit named group

Greedy and Lazy Quantifiers

Greedy Quantifiers(default): searches for the longest string
? Lazy Quantifiers: searches for the shortest string (more costly)

+-------------------+-----------------+----------------------------+
| Greedy quantifier | Lazy quantifier |       Description          |
+-------------------+-----------------+----------------------------+
| *                 |  *?             | Star Quantifier: 0 or more |
| +                 |  +?             | Plus Quantifier: 1 or more |
| ?                 |  ??             | Optional Quantifier: 0 or 1|
| {n}               |  {n}?           | Quantifier: exactly n      |
| {n,}              |  {n,}?          | Quantifier: n or more      |
| {n,m}             |  {n,m}?         | Quantifier: between n and m|
+-------------------+-----------------+----------------------------+
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