shell script how to switch users?

["Rajiv Jaisankar" <rajiv.jaisankar@xxxxxxxxx>]

Hi All,
i am not sure if this is the right mailing list for asking this question. I would appreciate any help on this.

I want to switch users using a shell script, i.e.
Say i am logged in as user1. I would like to say su - user2 in my script.
I would be performing some operations as user "user2" as part of the script after logging in as this user.
Finally i will be exiting back to user1 shell.

How will i login as user2 through shell script?
How will i  execute scripts as user2 after logging in from shell script? Even if i am able to login as user2
any commands after "su - user2" are not executed as user2. They are executed only as user1 when i exit the 
user2 shell.

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Regards,
Rajiv