Question

I would like to have your opinion on a simple regular expression I built to verify a list of comma separated file extensions (there could also be one or multiple spaces after or before the comma character).

This regular expression should return the following values:

$list = 'jpg,png,gif'; // valid
$list = 'jpg   , png, gif'; // valid
$list = 'jpg'; // valid
$list = 'jpg, png, gif'; // valid
$list = 'jpg png, gif'; // INVALID
$list = 'jpg png'; // INVALID

I am using the regular expression below, what do you think of it? can it optimized or shortened?

if(!preg_match( '#^[0-9a-zA-Z]+([ ]*,[ ]*[0-9a-zA-Z]+)*$#' , $list))
{
    echo 'invalid extension list';
} else{
    echo 'valid extension list';
}

Thanks for your good advices

Answer 1

You can also shorten it a bit:

preg_match('#^\w+(\s*,\s*\w+)*$#' , $list)