How to restrict spacebar in textarea input?

I've discovered a major security vulnerability in my website, I have a text form that uses its input as variables in a shell script. Long story short, ive determined that the simplest solution is to remove the spacebar from the text form (this form is meant for first names, so no space character is needed anyway) <input type=text required name="firstname" placeholder=" First Name" cols="30" rows="1" style="background-color:#000000;color:#FF0000;border:3px solid #FF0000;"> I need to know the easiest way to restrict the spacebar from this type of input. I have no experience with javascript or php, so I need extensive explanation on how to implement such methods to block the spacebar.