Escalating to a root shell

Question

(Continuing from here.)
Here's my situation:
Basically, I want to be able to escalate to root several times during the script, but not perform all commands as root. And I don't want to have to prompt the user for a password every time root privs are required because the process will be lengthy. The best way to do that would be to escalate the script into a shell with new permissions, but I don't know how.
I figure I have two practical solutions:
a)
In the script, start a new shell that continues execution from that point on.
Basically what I want is:
normal code
launch root shell
as root, spawn a shell as the original user
continue execution as original user
on a whim, exit the user shell back to the root shell to perform some root commands
get a new user shell to continue execution as the user
exit user shell
exit root shell
exit program
But I don't know how to launch a new shell and continue execution from that point.
b)
Fork off a process as root and loop while waiting for commands and send root commands to execute to it through a secure named pipe.
But I need the pipe to be secure (ie, don't want malicious programs to feed their own data into the pipe) but don't know how to secure a pipe.
(Alternative solutions are welcome too, the link points to my original question along these lines.)
I would prefer method b, but I'm really not choosy. I just want to perform building of packages and various setup therefore not as root, but be able to escalate to root for package installation.

Answer 1

ralvez wrote:
I think that what you need is a top-down approach.
You start the script with the higher level authority (root) and therefore you can su to any user in the system (without using a password) when you need to act as a regular user.
This script will get you started as root.
user=$UID
if [ $user != 0 ]
then
echo "Sorry. Only the ROOT user can run this program !"
exit
else
echo "###############( Updating Programs )###############"
echo
echo "Start: "
date
# su myuser
# other commands as user here
fi
Hope this helps.
R.
Wouldn't that switch over to a user session, effectively halting the script that is running in the root session until the user manually exits from the user session and then continue from the line after it the "su myuser" in the root session as the script is only running in the root session and not in the user session.