title: PHP - preg_match()
body: <p>Alright, so I want the user to be able to enter every character from A-Z and every number from 0-9, but I don't want them entering "special characters". </p>
  
  <p>Code: </p>
  
  <pre><code>if (preg_match("/^[a-zA-Z0-9]$/", $user_name)) {
      #Stuff
  }
  </code></pre>
  
  <p>How is it possible for it to check all of the characters given, and then check if those were matched? I've tried <code>preg_match_all()</code>, but I didn't honestly understand much of it. </p>
  
  <p>Like if a user entered "FaiL65Mal", I want it to allow it and move on. But if they enter "Fail{]^7(,", I want it to appear with an error. </p>