Question

Im creating a search function. The users are only allowed to use a-z A-Z and 0-9. How do i check if $var only contains text or numbers, and not special characters ?

I have tried something like this:

if (!preg_match('/[^a-z]/i', $search) {
$error = "error...";
}

If anyone have a smarter solution, please let me know. It could also be something checking for special characters.

Answer 1

You’re pretty much there. Just add numbers 0-9 to your regular expression, like this:

if(preg_match('/[^a-z0-9]/i', $search)) 
{
    $error = "Error...";
}

The /i flag tells the expression to ignore case, so A-Z is not needed inside the letter list.

In your original code, you were looking for anything that wasn’t a letter or number, while also checking to see if preg_match() hadn’t matched anything – you created a double negative. The code above executes the if() if anything that isn’t a letter or number is found. Full credit to @brain in the comments.

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To allow other characters, simply add them to the characters inside the braces:

if(preg_match('/[^a-z0-9 \.]/i', $search)) 
{
    $error = "Error...";
}

This example allows spaces and . (dots).