Question: Does PHP have global variables that can be modified by one running script and read by another?

Answer: 
Not as such, but you can use cookies or sessions to maintain data for duration of a user's browsing experience, or you can write to a database or file on-disk if the information needs to persist beyond that.
I made a tiny library (~2 KB; <100 lines) that allows you to do just this: [varDx](https://github.com/rahuldottech/varDx)

It has functions to write, read, modify, check and delete data.
It implements serialization, and therefore supports all data types.

Here's how you can use it:

```
<?php
require 'varDx.php';
$dx = new \varDx\cDX; //create an object
$dx->def('file.dat'); //define data file

$val1 = "this is a string";
$dx->write('data1', $val1); //writes key to file
echo $dx->read('data1'); //returns key value from file

```