Trouble with Gform field value $parameter name

Greetings, Unfortunately im not that great with PHP and my searching has yielded nothing. I am trying to "dynamically" fill in a field using the "Gform field value $parameter name". It works fine except I'd like to use a php variable (? i think it would be called that) e.g.

<?php
add_filter("gform_field_value_email", "populate_email");
function populate_email($value){
	$testyo = "blah";
   	return $testyo;
}

The above works.

<?php
$testyo = $client_email;
add_filter("gform_field_value_email", "populate_email");
function populate_email($value){
   	return $testyo;
}

But the above won't work. The $client_email is something that's defined further up. I'm sure the solution is simple and I'd appreciate any help. Forgive my ignorance.

Hello David. I appreciate the help. Your solution works. I am just having a little difficulty tying the funtions.php file with the page template file. I realise this falls out of the gravity forms scope and more into the general php help... but if you can help anyway it will be appriciated :)

Placing the below in the function.php file works.

<?php
$client_email = "lol";
$testyo = $client_email;
add_filter("gform_field_value_email", "populate_email");
function populate_email($value){
    global $testyo;
    return $testyo;
}

However $client_email is defined in the page template file (as this differs on a page by page basis). I tried the below in the functions.php file

<?php add_filter("gform_field_value_email", "populate_email");
function populate_email($value){
    global $value;
    return $value;
}

and the below in the page template file

<php
populate_email($client_email);

But that didn't seem to work. I probably don't understand the correct usage. I'm just playing a guessing game at the moment.

Hi David, I'm sorry it took so long to reply I was on holiday without a computer. Your code works if..

$client_email = "test@test.com";

is placed in the functions.php file. But it stops working as soon as I place it in the page template. Its weird, because I can echo $client_email and it shows fine, its just not connecting with gravity forms.

I found the problem. I don't know if you are familiar with the Pods plugin. Anyway, your lovely code worked fine on a normal Wordpress page template. But moving the same page template to the pods page caused the $client_email not to show. Its weird because if I put $client_email = "test@test.com"; in the functions file, it works fine. Its just if I try to declare $client_email = "test@test.com"; in the page template file that doesn't work. It must be to do with the way pods executes pages that isn't reading something.

Anyway thanks for your help. I really appreciate it.