Do do I wrote portable shell script?

hay guyz. I am trying to write some shell scripts to automate various processes (software installation in some cases, group account creation in others) on a variety of machines at this agency I volunteer with. What they have to work with are a bunch of different unices on a variety of hardware (some run bee-estee, some run linux, some run sun) and I'm pulling my hair out trying to write scripts that work on all machines!

So, I'm wondering, which shell is better for scrypting (languages like python and pearl are not available)? So far I've been trying to make things work with the linux boxes (we have more of those) but then they bomb when I run on the other boxes (I'm calling /bin/sh not /bin/bash, btw).

So, what shell should I write to for the sake of running everywhere? bee-estee? sun? korn? Have any of you come across this problem in the workplace and did you resolve it?

Thanks for you're help guys!

>>1
The best way to make portable shell script is to put the script into a box and put some wheels on the box. The important parts are the wheels.