PHP preg_replace - Print Variable Value Instead of Literal?

Basically, I'm working with jSON.

Pretty cool, but I can't decode it on my web host with json_decode();

Here's my solution:
PHP Regular Expressions to dynamically update jSON files.

Here's what I have, for example:

The jSON txt File
{

"person": {
"firstname":"Ricky",
"lastname":"Yoder",
"location":"Wernersville",
"haslived""Pottsville","Pottstown"]
}

}


The PHTML Web Page
<?php
$f=file_get_contents("test.txt");
$newfname="Richard";
die(nl2br(preg_replace('/"firstname":"(.*?)"/','"firstname":"($newfname)"',$f)));
die(nl2br($f));
?>


You see, I am trying to replace "firstname":"Ricky" with "firstname":"Richard", but since I have to use ' to make the delimiter, it is parsed as a literal, string, which gives us the output "firstname":"$newfname" instead of the actual value of the variable.

Is there any way to escape double quotes while using them to start the delimiter?

Your help is appreciated to make a more dynamic web.
-Ricky

We've all grown up. Cheers.