# Regular Expressions Cheat Sheet

#### Anchors

* `^`: start of the string or the start of a line in a multiline pattern
* `$`: end of the string or the end of a line in a multiline pattern
* `\b`: word boundary
* `\B`: not word boundary (opposite of `\b`)

Note: Anchors are non-quantifiable (i.e. cannot be followed by a quantifier).

#### Character sequences

* `.`: any character except line breaks
* `\w`: any word character
* `\W`: any non-word character (opposite of `\w`)
* `\s`: any whitespace character
* `\S`: any non-whitespace character (opposite of `\s`)
* `\d`: any digit character
* `\D`: any non-digit character (opposite of `\d`)
* `[abc]`: a single character in the given set (here `a`, `b` or `c`)
* `[^abc]`: a single character not in the given set (opposite of `[abc]`)
* `[a-z]`: a single character in the given range (here between `a` and `z` inclusive)
* `[^a-z]`: a single character not in the given range (opposite of `[a-z]`)
* `[a-zA-Z]`: a single character in either of the given ranges

Note: Use `\` to escape special characters (e.g. `\`, `/`, `[`, `]`, `(`, `)`, `{`, `}` etc.).

#### Quantifiers

* `a?`: zero or one of `a` (equal to `a{0,1}`)
* `a*`: zero or more of `a` (equal to `a{0,}`)
* `a+`: one or more of `a` (equal to `a{1,}`)
* `a{3}`: exactly 3 of `a`
* `a{3,}`: 3 or more of `a`
* `a{3,5}`: between 3 and 5 of `a` (inclusive)

Note: `a` is any valid quantifiable expression.

#### Groups

* `(ab)`: match and capture everything enclosed (here exactly `ab`)
* `(a|b)`: match and capture either one character (here `a` or `b`)
* `(?:ab)`: match everything enclosed, without capturing

#### Flags

* `g`: Global
* `m`: Multiline
* `i`: Case insensitive
* `u`: Unicode

Note that this cheatsheet is meant only as a starting point and is by no means a complete guide to all the features and nuances of regular expressions. You can also read 6 JavaScript Regular Expression features you can use today for a deeper dive into some more advanced features.


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