I'm certainly not a PowerShell expert but I have been finding my way around it lately. Once I got a few interesting scripts put together and saved to a file the next thing I ran up against was how do I launch these without loading them into the interactive environment by hand? By default when you install PowerShell it associates script files (.ps1 files) with notepad. Great for editing, not so great if you want to execute them. My guess is that after the 'Monad/PowerShell virus' story a year back or so that Microsoft got a little too freaked out to just let these things launch when clicked on. Unfortunately this decision also makes it more difficult to schedule a PowerShell script in the task scheduler too. To top it all off it's not quite as simple as just passing your script as a command line argument to PowerShell either. There are two separate steps necessary to enable you to launch PowerShell scripts from the Windows shell.

First you have to set up a file association in the Windows shell to change the default behavior for .ps1 files. However the PowerShell command line doesn't know what to do with a script file. By default it simple takes statements to execute. We can leverage this to our advantage though and construct a statement to cause our script file to be loaded and executed. That statement looks something like this:

powershell -command "& 'MyScript.psa1' "

If you update the file association with this you can then launch script files from the command line or by clicking on them. You can use the Tools | Folder Options dialog to do this but why not use PowerShell instead? Here are two simple lines of code to update your system registry to tell it how to execute .ps1 script files.

Note: This of course updates your system registry so you should back things up first.

new-item Registry::hkey_classes_root\microsoft.powershellscript.1\shell

new-item Registry::hkey_classes_root\microsoft.powershellscript.1\shell\open

new-item Registry::hkey_classes_root\microsoft.powershellscript.1\shell\open
\command -value ('"' + $PSHOME + '\powershell.exe" -command "& ''%1''"')

If you run these two PowerShell lines and then try and click on a .ps1 script file you'll see that we're not quite there yet. PowerShell has an execution policy that by default is set to "Restricted." In restricted mode no scripts are allowed to execute, only interactive commands may be executed. By using the PowerShell "set-executionpolicy" cmdlet you can change it to something more sensible like RemoteSigned which allows all locally generated scripts to execute but will only allow downloaded scripts to execute if they have been signed by a trusted source. In PowerShell you can execute the "help  about_signing" command for more info on this.

Once these two steps are done you can now launch PowerShell scripts directly without having to start up the interactive environment first. In addition you can also use this method to schedule PowerShell scripts in the task scheduler.

Flux and Mutability

The mutable notebook of David Jade