You may have seen this at the top of scripts or modules
#Requires –Version 3
This will stop the script running if the PowerShell version is 2.0 or below.
Other options are available
#Requires –PSSnapin can be used to force the loading of a snapin
#Requires –Modules can be used to force importing of modules
#Requires –Shellid controls which shells the script can run in. Default PowerShell installs have the ISE and console
#Requires –RunAsAdminstrator - script must be running in instance of PowerShell with elevated privileges
These provide a simple and easy way to control execution without lots of code. I particularly like the last one.