How can I use regex to validate usernames?

How can I use regex to validate usernames?

You can use a regex pattern like '^[a-zA-Z0-9_]{3,16}$' to validate usernames. This allows letters, numbers, and underscores, and limits the length.

What does each part of that regex mean?

The '^' asserts the start, '[a-zA-Z0-9_]' allows letters, numbers, and underscores, '{3,16}' sets the length between 3 and 16 characters, and '$' asserts the end.

Can I allow special characters too?

Yes, you can modify the regex to include special characters by adding them inside the brackets, like '^[a-zA-Z0-9_!@#$%^&*()]{3,16}$'.

What if I want to disallow certain characters?

You can use a negative lookahead. For example, '^(?!.*[!@#]).{3,16}$' disallows '!', '@', and '#', while still enforcing the length.