If you make snapshots of your Android device's screen sometimes, you might like following monkeyrunner script. It supports both the default ddms naming and also custom name that you can provide as parameter.
Finally you can wrap the monkeyrunner execution into shell script:
I am neither shell nor python guru, so if you can enhance it, let me know. For example, I am pretty sure one can manage to have everything in one single shell script but that would take too much time to me to find.