Chapter 9. The 10 PowerShell scripting commandments
James O’Neill
In my view, PowerShell succeeds because it provides a kit of small, general-purpose commands to be linked together to make larger, specific commands. Extending the toolkit is a good thing, and my approach to extending the toolkit can be summarized as “10 commandments” (which I jokingly call cmdments):
1. Create functions for reuse, scripts for a single task.
2. Choose names for commands and parameters wisely.
3. One task, one function: the “DoStuffWith” verb doesn’t exist for a reason.
4. Build flexibility into parameters.
5. Ask whether constants are better as defaults for parameters.
6. Ask “What could I receive?” and “What could I pass on?”
7. Use Write- and Out- cmdlets properly.
8. Use comment-based help, and include examples.
9. Learn to use the Try{} Catch{} scriptblocks; don’t rely on $ErrorActionPreference.
10. Choose either to support –WhatIf or to restore data.
This chapter will give you more insight into each commandment.
Scripts do a complete job—you can have “Download new pictures from my RSS feed.ps1” as a script that runs as a scheduled job and doesn’t rely on taking user input. Whereas scripts are specific and self-contained, functions do small jobs, like the built-in commands, and add tasks to the shell making them building blocks for scripts. Functions aim to be part of one or more bigger commands.
