Word Boundaries \b

The \b anchor matches the boundary between a word character and a non-word character.

What is a Word Boundary?

A word boundary exists:

• Between a word character (\w) and a non-word character (\W)
• At the start/end of the string if it begins/ends with a word character

Only the standalone word "cat" matches, not "cat" inside other words.

Without Boundaries

Without \b, "cat" matches everywhere it appears, including inside words.

Exercises

Start and End Boundaries

You can use \b at just the start or end:

Non-Word Boundary

\B matches where \b doesn't - inside words.

Practical Examples

Practice Playground

Try:

• \bjava\b - matches "java" only
• \bJava\b - matches "Java" only
• \b[Jj]ava\b - both cases
• \bJava\w* - words starting with Java

Key Takeaways

• \b matches word boundaries (edges of words)
• Use \bword\b to match whole words only
• \bprefix matches words starting with prefix
• suffix\b matches words ending with suffix
• \B matches non-boundaries (inside words)