cheetsheetz/regex.md

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
2. Character Classes
3. Quantifiers
4. Grouping and Capturing
5. Alternation
6. Assertions
7. Modifiers
8. Escape Characters
9. 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.