Execution of Shell Commands

I have a question:
Where would I put the Command line (of any command) so that it executes every time I log on? Where would I put it if I want it to execute every time I start a new shell?

That depends on your login shell. Is it bash?

From the man page:

This is different for other shells...

yes it is bash

---------- Post updated at 04:07 PM ---------- Previous update was at 03:47 PM ----------

Please explain it more !

From the man page:

thanks . what about for login shell ?

You're welcome. See post #2