Beginner: preg_match simple query (I hope)

[a1ias]

Been playing with this since early this fine Sunday morning and have decided to turn to the pro's for a little pointer.

 

The code I am having an issue with is as follows:-

 

<?php
$checkthis = 'a41$;wilsond';

if (preg_match('[^a-zA-Z0-9]', $checkthis)) {

  $checked = 'Bad String';

  } else {

  $checked = 'Good String';
}

echo $checked;

?>

 

What I am expecting that snippet to do is check the variable $checkthis for alphanumeric characters only, and since it contains both a $ and a ; I expect $checked to be returned as 'Bad String', which appears not to be the case...doh!

 

I have no doubt that I have made a simple beginners error, but am failing to understand why it does not work.

 

Any pointers are greatly appreciated.

 

 

a1ias

[Pikachu2000]

You omitted delimiters . . .

 

if (preg_match('~[^a-zA-Z0-9]~', $checkthis))

[a1ias]

Many many thanks for the help. I've also discovered that

if (preg_match('/[^a-zA-Z0-9]/', $checkthis))

works.

 

Is there a big difference between either of them and, as any documentation I have on regex is sketchy to say the least, what do those delimiters actually represent, if I may ask?

[Pikachu2000]

The delimiters can be be any non-alphanumeric character. Some people use slashes, some use other characters. You just need to use the same leading and trailing delimiter. It simply denotes the start and end of the pattern, so the one I posted and the one you posted after are effectively identical.