Replace text if it matches another piece of text

Question

So I have the following code to remove "page=" from a string. My problem now is that I want to query through "$qs_final" to check if it contains "price_range" and if so replace it with another piece of text. The price range variable is attached to "attr=" so I can't really use a $_GET request as other information is stored within it. The price_range variable also has the layout of "price_range_20".

<?php 
    $querystring = explode("&",$_SERVER['QUERY_STRING']);
    $qs_nos = 0;
    $qs_final = "";
    while(isset($querystring[$qs_nos])) {
        if(!ereg("page=",$querystring[$qs_nos])) {
            $qs_final .= $querystring[$qs_nos]."&";
        }
        $qs_nos++;
    }
    if (strpos($qs_final,'price_range') !== false) {
        print "true";
    }       
?>

Answer 1

str_replace().

$new_string = str_replace($what_to_replace, $what_to_replace_it_with, $old_string);

EDIT: To replace data, you need preg_replace(). In your case to remove "price_range" and all numbers and underscores directly after it, use this:

$new_string = preg_replace("/price_range[0-9_]+/", "", $old_string);