Continuing on from last time, I will now talk about writing re-usable scripts in PowerShell. Any command that we have executed at PowerShell command line can be dropped into a script file. I have lots of little PowerShell scripts for common tasks sitting in c:\Utilities\Scripts, which I include in my path. Let’s say that I want to stop all running copies of Cassini (aka the Visual Studio Web Development Server aka WebDev.WebServer.exe).
Stop-Process -name WebDev.WebServer.exe -ErrorAction SilentlyContinue
This will terminate all running copies of the above-named process. ErrorAction is a common parameter for all PowerShell commands that tells PowerShell to ignore failures. (By default, Stop-Process would fail if no processes with that name were found.)
We’ve got our command. Now we want to turn it into a script so that we don’t have to type it every time. Simply create a new text file with the above command text called “Stop-Cassini.ps1” on your desktop using the text editor of your choice. (The script can be in any directory, but we’ll put it on our desktop to start.) Let’s execute the script by typing the following at the PowerShell prompt:
What just happened? Why can’t PowerShell find my script? By default, PowerShell doesn’t include the current directory in its search path, unlike cmd.exe. To run a script from the current directory, type the following:
Another option is to add the current directory to the search path by modifying Computer… Properties… Advanced… Environment Variables… Path. Or you can modify it for the current PowerShell session using:
$env:Path += ‘.\;’
($env: provides access to environment variables in PowerShell. Try $env:ComputerName, $env:OS, $env:NUMBER_OF_PROCESSORS, etc.)
You could also modify your PowerShell startup script, but we’ll talk about that in a future instalment. Let’s run our script again:
No dice again. By default, PowerShell does not allow unsigned scripts to run. This is a good policy on servers, but is a royal pain on your own machine. That means that every time you create or edit a script, you have to sign it. This doesn’t promote the use of quick scripts for simplifying development and administration tasks. So I turn off the requirement for script signing by running the following command from an elevated (aka Administrator) PowerShell prompt:
If this command fails with an access denied error:
then make sure that you launched a new PowerShell prompt via right-click Run as administrator…
Third time is the charm…
We are now able to write and use re-usable scripts in PowerShell. In my next instalment, we’ll start pulling apart some more complicated scripts that simplify common developer tasks.
UPDATE: As pointed out by Josh in the comments, setting your execution policy to RemoteSigned (rather than Unrestricted) is a better idea. Downloaded scripts will require you to unblock them (Right-click… Properties… Unblock or ZoneStripper if you have a lot) before execution. Thanks for the correction.