This assumes you are familiar with the basic usage of the Gateway Migration Utility and that you've created an encoded password.
The GMU commands can get quite lengthy. To reduce the length of the commands, common options can be stored in files. As an example, the example.properties files could contains common options used when making a restman call to the dev internal API Gateway.
trustCertificate trustHostname host=example.com port=8443 username=your_username password=your_encoded_password