Hello, does anyone know how to do a small script which checks that a username can be a username.

Im talking about the special charactes and spaces which can't be used when creating a username.

So a user writes: "kevin little" in this case this can't be a username as it contains space.

or
"kevin\little" in this case this can't be a username as it contains special character '\'.

or
"kevin_little" in this case it can be a username as there are only accepted charactes.

If someone knows how to do this please let me know.

Thank you.

You could use bash regular expressions:
(or grep if it needs to be portable to older versions of bash).

OK, but this is only normal characters, what about '-' '_' or '.' ?

Hi,

Officially this is the legal template for a linux/unix username: [a-z_][a-z0-9_-]*

The only character missing in post #2 is a _ (twice)

^[a-z][-a-z0-9]*$ should be ^[a-z_][-a-z0-9_]*$

Hope this helps.

Yes, it helps.

Thank you very much for the help!

You're welcome