Executing SU in a bash script
Solution 1:
sudo starts a shell unless you instruct it otherwise.
It looks like you actually want to run this script as another user. To do that, try something like this:
#!/bin/bash
if [ `id -nu` != diy ]; then
sudo -u diy $0 # Re-run this script as user diy
else
# Everything you want to do goes here
fi
Keep in mind that /etc/sudoers must be set up to allow the original user to run this script as the new user.