30
On *nix:
$ recipient="email@example.com" php script.php
<?php
print_r($_SERVER);
Test:
$ recipient="email@example.com" php script.php | grep recipient
[recipient] => something@example.com
Or, you can export it or setenv (depending on your OS), like
$ export recipient="email@example.com"
$ setenv recipient="email@example.com"