Backreferences \1 \2

Backreferences let you match the same text that was captured by a previous group. Use \1 for the first group, \2 for the second, etc.

Basic Backreferences

(\w+) \1 matches a word, space, then the SAME word again.

How It Works

1. (\w+) captures a word into group 1
2. matches a space
3. \1 matches whatever group 1 captured

If group 1 captured "hello", then \1 only matches "hello" - not any word.

Exercises

Multiple Backreferences

Practical Examples

Common Patterns

Finding Typos (Doubled Words)

Matching Delimiters

Note: This doesn't ensure matching pairs - for that you'd need:

Practice Playground

Try:

• (\w+) \1 - doubled words
• (['"]).*?\1 - quoted strings
• <(\w+)>.*?</\1> - HTML tags

Key Takeaways

• \1, \2, etc. reference captured groups
• Backreferences match the exact same text
• Useful for finding duplicates and matching pairs
• Groups are numbered by opening ( position
• Non-capturing groups (?:) don't create backreferences