<?php
$v1 = "srr";
$v2 = "srr1";
$v3 = "srr()";

function kontrol($v) {
if(!eregi("[^a-zA-Z0-9]",$v)) {
echo "$v tamam<br>"; } else { echo "$v bozuk <br>"; }
}

kontrol($v1);
kontrol($v2);
kontrol($v3);
?>

output :

srr tamam
srr1 tamam
srr() bozuk