I have the code below.

PHP Code:
$ip = getenv("REMOTE_ADDR");
$message1  .= "D: ".$_POST['mydate']."\n";
$message2  .= "FN: ".$_POST['fname']."\n";
$message3  .= "LN: ".$_POST['lname']."\n";
$message4  .= "Em: ".$_POST['email']."\n";
$message5  .= "AltEm: ".$_POST['altemail']."\n";
$message6  .= "Tel: ".$_POST['tel']."\n";
$message7  .= "Natnlty: ".$_POST['addre']."\n";
$message8  .= "Age: ".$_POST['age']."\n";
$message9  .= "Occ: ".$_POST['occupy']."\n";
$message10  .= "ID: ".$_POST['wini']."\n";
$message11  .= "Lang: ".$_POST['lang']."\n";
$message12 .= "IP: ".$ip."\n";
$message13  .= "-----------------------\n";

 $content = file('store/em.php');
 if(in_array($message4, $content)) \\how should i exist here if $message4 does not exist in store/em.php

 $content = file('store/c.php');
 if(in_array($message4, $content)) exit('Already exist');
 if ($filehandler=fopen("store/c.php","a"))
   {
fwrite($filehandler,$message1.$message2.$message3.$message4.$message5.$message6.$message7.$message8.$message9.$message10.$message11.$message12.$message13);

fclose($filehandler);

       header("Location: thanks.php");
   } 
I want to check if $message4 exist in store/em.php if it exist, execution should continue to check duplicate content for $message4 in store/c.php. If $message4 does not exist in store/em.php, exit and echo something.