question about switch function

Hello, I am trying to find out if a string is in a line being read from a file. I should use strstr for this I am pretty sure. I want to do something like this: switch(strstr($line, case argument)) but I don't know if it is possible. For example, I am looking for Zip in a line but it will not find it using the code below. Any suggestions? I know I am being as clear as mud on this :) $fd = fopen("mls1.txt", "r"); while(!feof($fd)) { $line=fgets($fd, 4096); switch($line) { case "Zip": echo "found zip"; //$line2=fgets($fd,4096); $zip=$line; break; case "Remarks": //$line2=fgets($fd,4096); $neighborhood=$line; break; case "Taxes": //$line2=fgets($fd,4096); $address=$line; break; } } fclose($fd);