I used ‘cls’ for it does clear screen and ls.
After I upgraded my ubuntu, i can’t use that any more. It showed:
cls: command not found
Finally I have found the solution.
You have to create a alias for the command you want to use.
For example, for cls
$ alias cls='clear;ls'
You can make more aliases,
$ alias cll='clear;ls -lh'
These aliases will vanish on your next login. So to make the change permanent you can add it to your ~/.bashrc or ~/.bash_profile. Just add the whole alias line as these files are executed (as bash scripts) on login.