It is safe to use non-escaped Windows-style filenames in your single-quoted strings

 
<?php
            $filename = 'c:\windows\me.txt';
            echo $filename;
    ?>

1.	Double quotation marks allow the parsing of variables
2.	Double-quoted string escape sequences
3.	Double-quoted strings
4.	If you use single quotation marks to enclose the same string, the variable is not substituted:
5.	Using forward slashes on Windows
6.	Fixing quote escaping in backreference replacements
7.	Various special characters in string assignments

It is safe to use non-escaped Windows-style filenames in your single-quoted strings : Quotation « String « PHP