functions.php script breaks when variable isn't hard coded - php

Question

I have written a jQuery script that takes a JSON encoded list produced with this function is run in my theme's functions.php and creates a playlist for my jPlayer. However, the script only works when the $file variable is hard coded (for example, OH0400). But I need it to pick up the $file variable based on the page being loaded. But when I switch to this method (using URL), the script says the JSON is null.
I've run the script in multiple ways and the output between the hard coded $file and the variable based $file appear to be the same. Why do I get null when I make the switch?
Here's the PHP in my theme functions.php.
function MyjPlayerList(){
$url = explode( '/', $_SERVER['REQUEST_URI'] );
$file = strtoupper($url[2]);
//$file = 'OH0400';
$filename = '/dir/oralhistory/mp3files/'.$file.'*.mp3';
$FILES = glob( $filename );
foreach( $FILES as $key => $mp3 ) {
$mp3 = str_replace( '/dir/oralhistory/mp3files/', '',$mp3);
$FILE_LIST[ $key ][ 'title' ] = $mp3;
$FILE_LIST[ $key ][ 'mp3' ] = 'http://websiteurl.org/mp3files/'.$mp3;
}
$myjplayerdata = json_encode( $FILE_LIST );
header ( 'Content-type: application/json' );
echo $myjplayerdata;
exit;
die();
};
Here is my javascript:
ajax_player = function() {
jQuery('div#player').load('/js/player.html' , function() {
var cssSelector= {
jPlayer: "#jquery_jplayer_1",
cssSelectorAncestor: "#jp_container_1"
};
var playlist = [];
var options = {
swfPath: "/js/Jplayer.swf",
supplied: "mp3",
smoothPlayBar: true,
keyEnabled: true
};
var myPlaylist = new jPlayerPlaylist(cssSelector, playlist, options);
jQuery.ajax({
url: "/wp-admin/admin-ajax.php" ,
type: "POST",
dataType: "text json",
data: { action: "MyjPlayerList"},
success:(function(data) {
jQuery.each(data, function(index, value){
myPlaylist.add(value); // add each element in data in myPlaylist
console.log(data);
})
})//function (data) close
})//ajax close
})//jquery.load
}//ajax_player

Answer 1

Yes, check the character encoding you're using. That could be the problem.

Answer 2

thanks to the debugging of Marc,turns out that what I get when i run the script in page & what i get when I call the script w/ javascript are different. it's trying to glob admin-ajax.php instead of the URL.