Can't pass a PHP variable to file_get_contents()
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I am a newbie coder trying to build a simple web app using PHP. I am trying to send an HTML email that has a variable that will change each time it is sent.  The code to initiate the email is 'email.php' and contains:

$body = file_get_contents('welcome/green2.html.php');

Within the 'green2.html.php' file, I have a variable called $highlight that needs to be populated. The $highlight variable is defined within the 'email.php' file.  I had tried to simply add <?php html($highlight) ?> within the 'green2.html.php' file, however it is not being parsed.  I get a blank space where the variable should be when it is output. 

Also, I have done an include 'welcome/green2.html.php' within the 'email.php' file.  When I echo it, the $highlight var is shown on the resulting page, but not if I echo $body.  

Any help would be much appreciated!

Orange Twine