<?php
$str = '$str = "this is an \\" example of some input"; $but = "this is \\\\\\" another example\\" of input"; $and = "and here be one more\\\\"';

echo $str . "\n";

preg_match_all('~("(?:\\\\.|[^"])+?")~',$str,$match);

print_r($match);

/*
Output:
$str = "this is an \" example of some input"; $but = "this is \\\" another example\" of input"; $and = "and here be one more\\"
Array
(
    [0] => Array
        (
            [0] => "this is an \" example of some input"
            [1] => "this is \\\" another example\" of input"
            [2] => "and here be one more\\"
        )

    [1] => Array
        (
            [0] => "this is an \" example of some input"
            [1] => "this is \\\" another example\" of input"
            [2] => "and here be one more\\"
        )

)
*/
?>