* review the ls command

* review the cd command

* review the tac command

* review the head command

* review the tail command

* review the pwd command

* review touch command

* review cal command

* review bc command

* review df

* review the help command

* review the kill command

* review the ps command

* review the cp command

* review the lscpu command

* review the login command

* review the history command

* review the whoami command

* review the w command

* review the passwd command

* review the man command

* review the groups command

* review the finger command

* review the echo command

* review the sl command

* review the free command

* review the who command

* review the whatis command

* review the gzip command

* review mkdir