I was setting up a programming environment and I went to run my Main.exe and due to lack of sleep I left out the .exe. To my surprise the mouse properties dialog opened up. I knew my hello world app wasn't magically opening up mouse properties so I ran a quick Get-Command Main and it spat out C:\Windows\system32\main.cpl. So I guess the real question here is why does C:\Windows\system32\main.cpl open up my mouse properties?
Why does running "main" in PowerShell open my mouse properties
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2 Answers
The .cpl extension is for control panel items, and the default "open with" is the control.exe executable. So when you enter main into your terminal, it is opening main.cpl with the control.exe executable, which is opens the mouse portion of the control panel. I have no idea why they chose to use main.cpl for the mouse properties, but here is a list of various other .cpl's to use with control.exe: https://support.microsoft.com/en-ie/help/149648/description-of-control-panel--cpl-files, also check out: https://www.lifewire.com/command-line-commands-for-control-panel-applets-2626060
I have actually used the mmsys.cpl to automate switching of sound devices.
main.cpl is the Windows Control Panel module (.cpl) for mouse and input. As you found, when PowerShell cannot find a suitable command to to invoke for the input--Main in this case--it searches for an alternative program in the PATH.
It just so happens that the name of this module matches a commonly used naming pattern. C:\Windows\System32 is typically included in a Windows environment's PATH.
PS> Write-Output $env:PATH
C:\WINDOWS\system32;C:\WINDOWS;...
PS> Get-Command Main
CommandType Name Version Source
----------- ---- ------- ------
Application main.cpl 10.0.15... C:\WINDOWS\system32\main.cpl
The mouse properties is the default view for main.cpl, but we can also launch keyboard properties in a similar fashion:
PS> main keyboard
Or, more correctly:
PS> control.exe keyboard
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