Regular Expression for alphanumeric and underscores

Question

I wanted to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores. Is it possible? If yes how can I do it ?

Answer 1

To match a string that contains only those characters (or an empty string), try:

"^[a-zA-Z0-9_]*$"

Note this this will help you:

^ : start of string
[ : beginning of character group
a-z : any lowercase letter
A-Z : any uppercase letter
0-9 : any digit
_ : underscore
] : end of character group
* : zero or more of the given characters
$ : end of string

If you don't want to allow empty strings, use + instead of *.