Question

For only alpha numeric characters I use something like this:

<input type="text" pattern="[a-zA-Z0-9]+" />

When the data reaches the server I need to validate again. So I did

preg_match("[a-zA-Z0-9]+", $value);

But PHP says Warning: preg_match() [function.preg-match]: Unknown modifier ‘+’

Can’t you use the same expressions in html5 and PHP?

Edit:
I have a JSfiddle showing the suggestions below don’t work:
http://jsfiddle.net/EY3hc/

What I want to achieve is 1 regex I can use as pattern in html and in preg_match. The html is generated by PHP so I’d like to have one place to maintain code for validation.

Answer 1

You need to add delimiters in your expression. Also you should match the beginning and end of the line:

preg_match("/^[a-zA-Z0-9]+$/", $value);

Without ^ and $, an input like somewords!@# would validate.