How can I validate a string to only allow alphanumeric characters in it?

Question

How can I validate a string using Regular Expressions to only allow alphanumeric characters in it?

(I don\'t want to allow for any spaces either).

Answer 1

^\w+$ will allow a-zA-Z0-9_

Use ^[a-zA-Z0-9]+$ to disallow underscore.

Note that both of these require the string not to be empty. Using * instead of + allows empty strings.