<?php
$str1 = 'single quote';
$str2 = "double quote";
?>

<?php
/*
    string function str_parse(string $string, array $variables)
    
 Takes $string and parses as if it was double quoted.
 $variables must be an associative array. All keys must be able to
    be used as regular PHP varibles.
    
    Returns parsed $string.
    
    Usage:
 $varible = 'I\'m a single quoted string!';
 $string = '$variable';
 echo $string;
 //Prints $string as "$variable".
 
 $variables = array(
     'variable' => $variable);
 echo str_parse($string, $variables);
 //Prints $string as "I'm a single quoted string!".
*/
function str_parse($string, &$valArr) {
    //Save a md5 hash of the orginal string to check against.
    $string_back = md5($string);
    
    //Loop through our variable array.
    foreach($valArr as $key => $val) {
 $$key = $val;
    }
    //Check to see if we have the same string as before.
    //If we don't then it was a single quoted string.
    if(md5($string) == $string_back) {
 $i = 0;
 foreach($valArr as $key => $val) { $s[$i] = "\${$key}"; $r[$i++] = $val; }
 return str_replace($s, $r, $string);
    //Else it was and we can just return it.
    } else {
 return $string;
    }
}
?>

$foo = 'world';
$bar = 'Hello, $foo.';
eval("\$baz = \"$bar\";");
print $baz;