Alternation (OR) |

The pipe | acts as an OR operator, matching either the pattern on the left or the right.

Basic Alternation

Matches either "cat" OR "dog".

Exercises

Alternation with Groups

Without groups, alternation applies to the entire pattern on each side:

This matches "I love cats" OR "dogs" - probably not what you want!

Use groups to limit alternation scope:

Now it matches "I love cats" OR "I love dogs".

Practical Examples

Order Matters

Alternatives are tried left to right. The first match wins:

Since "cat" is first, it matches before "category" can be fully matched.

Now "category" matches fully because it's tried first.

Practice Playground

Try:

• http|ftp - protocols
• active|inactive|pending - status values
• @\w+|email - social or email

Key Takeaways

• a|b matches a OR b
• Chain multiple alternatives: a|b|c|d
• Use groups to limit scope: prefix(a|b|c)
• Order matters - first match wins
• Combine with other patterns freely