# RegEx Cheatsheet

Contents:

1. [Special characters](#special-characters)
2. [Quantifiers](#quantifiers)
3. [Special sequences](#special-sequences)
4. [Useful examples](#useful-examples)


## Special characters

- `\` - escapes special characters
- `.` - matches any character
- `^` - matches start of the string (or line if MULTILINE)
- `$` - matches end of the string (or line if MULTILINE)
- `[5b-d]` - matches any chars '5', 'b', 'c' or 'd'
- `[^a-c6]` - matches any char except 'a', 'b', 'c' or '6'
- `R|S`- matches either regex R or regex S
- `()` - creates a capture group, and indicates precedence


## Quantifiers

- `*` - 0 or more
- `+` - 1 or more
- `?` - 0 or 1
- `{m}` - exactly 'm'
- `{m,n}` - from m to n (`m` defaults to 0, `n` to infinity)
- `{m,n}?` - from m to n, as few as possible


## Special sequences

- `\A` - Start of string
- `\b` - Matches empty string at word boundary (between \w and \W)
- `\B` - Matches empty string not at word boundary
- `\d` - Digit
- `\D` - Non-digit
- `\s` - Whitespace: [ \t\n\r\f\v], more if LOCALE or UNICODE
- `\S` - Non-whitespace
- `\w` - Alphanumeric: [0-9a-zA-Z_], or is LOCALE dependant
- `\W` - Non-alphanumeric
- `\Z` - End of string


## Useful examples

Find `foo` word:

```
\bfoo\b
```

Find a sequence of `foo` + some characters + `bar`:

```
\bfoo\b.*\bbarb\
```