Another way could be making cases and passing a parameter to the executed script.
Example could be:
First make a file called "script.sh".
Then insert this code in it:
#!/bin/sh
my_function() {
echo "this is my function."
}
my_second_function() {
echo "this is my second function."
}
case "$1" in
'do_my_function')
my_function
;;
'do_my_second_function')
my_second_function
;;
*) #default execute
my_function
esac
After adding the above code run these commands to see it in action:
root@shell:/# chmod +x script.sh #This will make the file executable
root@shell:/# ./script.sh #This will run the script without any parameters, triggering the default action.
this is my function.
root@shell:/# ./script.sh do_my_second_function #Executing the script with parameter
this function is my second one.
root@shell:/#
To make this work as you required you'll just need to run
su username -c '/path/to/script.sh do_my_second_function'
and everything should be working fine.
Hope this helps :)