How to Write and Test Regular Expressions: A Beginner to Advanced Guide

Regular expressions, commonly referred to as Regex, are search patterns used to match and manipulate text characters in strings.

Basic Syntax Tokens

• .: Matches any single character except newline.
• ^: Matches the start of the string line.
• $: Matches the end of the string line.
• *: Matches 0 or more occurrences of the preceding token.
• +: Matches 1 or more occurrences of the preceding token.
• ?: Matches 0 or 1 occurrence of the preceding token (or makes a quantifier lazy).

Advanced Techniques: Groups and Toggles

• Character Sets `[...]`: Matches any character inside the brackets. (e.g. [a-z] matches lowercase letters).
• Capture Groups `(...)`: Isolates parts of your match to extract them.
• Flags: Tweak how matching behaves:
• g (global): Find all matches rather than stopping at the first match.
• i (case-insensitive): Ignore case.
• m (multiline): Match boundary symbols ^ and $ across lines.