Well of course that won't work - the exec() function is for running commands on the operating system, not for requesting URLs with a query string from a web server over a network.
Since you sound relatively new to programming, here is a tutorial you should read:
Using PHP-CLI (Command Line Interface)
And if you really want to run your PHP script as CGI, then you're going to have to use an HTTP client like wget or lynx. In other words in Perl you would do:
$content = `wget -O - http://example.com/script.php?name=value`;
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