Shell Programming and Scripting

Normally i would google, but I did not know how to google the problem I am facing now also being a newbie in shell scripting.
Okay, the requirement is
user1 has sudo rule to su - user2(NO PASSWORD) and user2 has will be able to sudo certain commands
so following works fine from command prompt
user1@host] sudo su - user2
the above command opens up a new shell, logging me in as user2
user2@host] sudo cmd1
user2@host] sudo cmd2
user2@host] sudo cmd3
user2@host] exit
user1@host]
How would I achieve the above using a shell script?
I have tried putting following commands in a shell script
sudo su - user2 -c "sudo cmd1" (this prompts me for a password though I have a sudo rule to not prompt for one.)
sudo su - user2 (this gets me out of the shell and takes me to "user2@host]")
none works for me.
Any help on this would be greatly appreciated.

Why not allow user1 to call cmd1, cmd2 and cmd3 as user2 without password:

Code:

# Example of change to /etc/sudoers
Cmnd_Alias      U2CMDS = /usr/local/bin/cmd1, /usr/local/bin/cmd2, /usr/local/bin/cmd3

# Allow user1 to run cmd(1-3) as user2 without password
user1  ALL=(user2)  NOPASSWD: U2CMDS

then user1 can:

Code:

user1@host] sudo -u user2 cmd1
user1@host] sudo -u user2 cmd2
user1@host] sudo -u user2 cmd3

Or, if you do it a lot and always call cmd1 then cmd2 then cmd3 put these three calls into 1 script that user1 can call.

set the sudo command to group, not to single user.

With that, you can easily manage the sudo list.