As a user, I would like to run a simple script on all UNIX platforms

So I'm trying for a long time to write an acceptable script that installs telegraf on the provisioned VMs. After being advised that I should cover all platforms, and not a subset, and after being advised to put my code in a function and call it, here is what I have come up with for the UNIX platforms:

https://git.qt.io/snippets/1595
(EDIT2: there were some problems with script visibility, it should now be visible to everyone, logged-in or not)

• This has the problem that it depends on some COINAGENT_* variables, that I'm currently setting in my patched Coin. This was deemed wrong however, as provisioning scripts should be runnable even outside Coin.
• I could do all the OS detection etc in a shell script that would be automatically sourced by all provisioning, but there is no way to auto-source a common script (at least not without heavy refactoring of provisioning)
• I could do all this only for the telegraf script but then it wouldn't be generic, and it would make the simple script above quite complex.

What is the right way to move forward with this?