Use $variable from file1.php in file2.php (different file paths)

Store the value is a function or make it global;

function get_variable_1(){

    return 5;

}

OR

global $variable_1;
$variable_1 = 5;

But.. really, what you need to do it to read a bit more about the basic of PHP to understand how variables and functions work – global variables are not really a good idea and neither are functions which single return values with accepting arguments.. so you need to plan your PHP application to use both concepts correctly.