?php
$str = "Hello world. (can you hear me?)";
echo quotemeta($str);
?>

quotemeta( _string_ )

?php 
$str1 = "1 + 1 = 2"; 
$str2 = "1 * 1 = 1"; 
$str3 = "Could you borrow me 5$?"; 
$str4 = "Are you not entertained? (I am..)"; 
$str5 = "The caret [ ^ ] Looks like a hat!"; 
echo quotemeta($str1)."br>"; 
echo quotemeta($str2)."br>"; 
echo quotemeta($str3)."br>"; 
echo quotemeta($str4)."br>"; 
echo quotemeta($str5)."br>"; 
?>