Regex Tester

Build and test regular expressions against sample text.

Regular Expression:

Global (g) Case-Insensitive (i) Multi-line (m)

Sample Text:

Results:

Understanding Regular Expressions

A Regular Expression (Regex) is a sequence of characters that defines a search pattern. It's an incredibly powerful tool for pattern matching within strings, used for tasks like searching, replacing, and validating text.

Why Use a Regex Tester?

Building Complex Patterns: Regex syntax can be intricate. A tester allows you to build and refine your expressions incrementally.
Real-time Feedback: See exactly what your regex matches (or doesn't match) in your sample text.
Debugging: Identify errors or unexpected behavior in your regex patterns quickly.
Learning: Experiment with different regex components and flags to understand their effects.

Regex Components:

Character Classes

.: any character except newline
\\w\\d\\s: word, digit, whitespace
\\W\\D\\S: not word, digit, whitespace
[abc]: any of a, b, or c
[^abc]: not a, b, or c
[a-g]: character between a & g

Anchors

^$: start / end of the string
\\b\\B: word, not-word boundary

Escaped Characters

\\.\\*\\\\: escaped special characters
\\t\\n\\r: tab, linefeed, carriage return

Groups & Lookaround

(abc): capture group
\\1: backreference to group #1
(?:abc): non-capturing group
(?=abc): positive lookahead
(?!abc): negative lookahead

Quantifiers & Alternation

a*a+a?: 0 or more, 1 or more, 0 or 1
a{5}a{2,}: exactly five, two or more
a{1,3}: between one & three
a+?a{2,}?: match as few as possible
ab|cd: match ab or cd