# Regular Expressions (Regex) Cheat Sheet

In this cheat sheet, we'll explore common Regular Expressions (regex) patterns and their meanings.

## Table of Contents

1. [Anchors](#anchors)
2. [Character Classes](#character-classes)
3. [Quantifiers](#quantifiers)
4. [Grouping and Capturing](#grouping-and-capturing)
5. [Alternation](#alternation)
6. [Assertions](#assertions)
7. [Modifiers](#modifiers)
8. [Escape Characters](#escape-characters)
9. [Special Characters](#special-characters)

## Anchors

- `^`: Asserts the start of a line.
- `$`: Asserts the end of a line.
- `\b`: Asserts a word boundary.
- `\B`: Asserts a non-word boundary.

## Character Classes

- `.`: Matches any single character except a newline.
- `[abc]`: Matches any one of the characters a, b, or c.
- `[^abc]`: Matches any character except a, b, or c.
- `[a-z]`: Matches any lowercase letter.
- `[A-Z]`: Matches any uppercase letter.
- `[0-9]`: Matches any digit.
- `\d`: Matches any digit (short for `[0-9]`).
- `\D`: Matches any non-digit.
- `\w`: Matches any word character (alphanumeric + underscore).
- `\W`: Matches any non-word character.
- `\s`: Matches any whitespace character.
- `\S`: Matches any non-whitespace character.

## Quantifiers

- `*`: Matches 0 or more occurrences of the preceding character or group.
- `+`: Matches 1 or more occurrences of the preceding character or group.
- `?`: Matches 0 or 1 occurrence of the preceding character or group.
- `{n}`: Matches exactly n occurrences of the preceding character or group.
- `{n,}`: Matches n or more occurrences of the preceding character or group.
- `{n,m}`: Matches between n and m occurrences of the preceding character or group.

## Grouping and Capturing

- `(...)`: Groups patterns together. Captures the matched text.
- `(?:...)`: Groups patterns together without capturing.
- `\1`, `\2`, ...: Refers to the first, second, etc. captured group.

## Alternation

- `|`: Acts like a logical OR. Matches the pattern before or after the pipe.

## Assertions

- `(?=...)`: Positive lookahead assertion.
- `(?!...)`: Negative lookahead assertion.
- `(?<=...)`: Positive lookbehind assertion.
- `(?<!...)`: Negative lookbehind assertion.

## Modifiers

- `i`: Case-insensitive matching.
- `g`: Global matching (find all matches).
- `m`: Multiline matching (`^` and `$` match the start/end of each line).

## Escape Characters

- `\`: Escapes a special character, allowing it to be treated as a literal.

## Special Characters

- `*`, `+`, `?`, `{`, `}`, `|`, `()`, `[]`, `.`, `\`: Special characters with their literal meanings when escaped.