Don't allow a form to have spaces or certain characters.

[AndrewWest]

I want to limit a form to only allow things like.

• Letters
• Numbers
• Underscore _

I don't want to allow:

~!@#$%^{&*()-|\=+/.,<>?;:'"[{]}} or any of those crappy special chars.

How would I limit a form to this in PHP?

[LordShryku]

if(eregi("[^a-z0-9_]", $string)) {
   echo "Invalid characters";
}
else {
   echo "Valid";
}

[TheDefender]

2 options:

Client Side via JavaScript... Best to post question in a JavaScript forum. This would validate immediately, either by limiting the field entry, or popup some alert or something if the wrong char is in it.

OR

Server Side via PHP. Regexp is needed. (This kind of validation would need to be done after the submission, and if the chars are there, either just dump them, or report an error to the user telling them to go back and make the corrections.

So first, you gotta decide which method you would prefer...

[LordShryku]

Use both. Javascript can be turned off, but is more convenient to someone who has it turned on.

[TheDefender]

Note - I agree with LordShryku on that... Implement both, because you never know what kind of crowd you are catering to, and this gives you 2 lines of defense....

[AndrewWest]

Alright I'll implement both, does anyone know how to do this in JavaScript also?