The command line interface was a pet project. The idea was to provide convenient ways to preform different actions. The long term goal was to have anything possible in the dev console possible in the command line, as well as allow force.com developers to add commands. Eventually creating a community of command line tools.
The current commands are not useful, and it isn't really used by anyone. Those commands were just an initial set to show the concept. However, it never got traction and priorities eventually downed out the project. I don't think any development has been done on it since initial checkin.
If it did get traction, grep was definitely on the list to add. Another useful tool would be to stream content from existing and incoming logs. For example, let's say you are logging a user who is generating a lot of logs and all you want to see is debug statements and exceptions. Something like the following would not only grep all the existing logs generated by the user, but also grep any new logs generated by the user:
stream logs [email protected] | grep 'DEBUG\|exception'
Or maybe you just set a couple heapdump and you really only care about one variable. You could do something like:
stream heaps className | show myVariable