A good tool for shell is ctrl + R, wich can retrieve a command that you entered a long time ago by keywords.

Ex.:
- you did "rm -Rf avatar.jpg"
- if you press ctrl + r and type "ava" it will show the command, if you press it again it'll show you another command with "ava" on it
- if you press enter, the command will run

Try it in your linux...

Where's it in our n900 shell?