Resolve $Linux error

[dsolodow]

This resolves #996.

Tested on:
Windows 10 x64 Education Build 17127 (Windows PowerShell 5.1)
Windows 10 x64 Education Build 17127 (PowerShell Core 6.0.2)
Ubuntu 16.04 (PowerShell Core 6.0.2)

[TylerLeonhardt]

@dsolodow you're on FIRE🔥 today. This looks fine to me although I'm not sure if $env:windir -ne $null applies in older versions of PowerShell since we technically still support PS 3 and up.

What you could do is take advantage of the $IsWindows variable in PSCore.

If it's True or null (which would mean it's Windows PowerShell), then we can do the logic.

Just a thought.

[dsolodow]

@tylerl0706 - good point.
The $env:windir -ne $null works as far back as Windows PowerShell 2.0 (just verified it on a Server 2008 R2 box).

I had originally thought about doing something with psversiontable (psedition and platform) but it was going to be fuglier. I didn't know about the $IsWindows as I've not dipped my toes much into PSCore yet.

It would be easy enough to switch over if that's preferred by the team.

[rjmholt]

Was going to say $IsWindows would be more readable, but tbh (($IsWindows -eq $null) -or $IsWindows) is pretty mystifying. The only advantage is that if someone defines export windir="something" on a Unix-like system, they break the $env:windir check.

[rjmholt]

So I'm happy with either too

[rkeithhill]

For this kind of test, I usually use if (($PSVersionTable.PSVersion.Major -le 5) -or $IsWindows) { i.e. if the platform is <= v5 then it is Windows. If it is v6 or higher then $IsWindows will be set appropriately. But there are several different ways to do this check that is valid across versions & platforms.

I prefer the above test because it uses PowerShell built-in variables. Env vars are controlled by the user and there is nothing stopping a Linux/macOS user from defining a windir env var.

[rjmholt]

Yeah that seems like the right way to test this

[TylerLeonhardt]

Yep makes sense. The bug was opened because of StrictMode and I think what Keith said should play nice with it as well.

[dsolodow]

That makes sense; fewer opportunities for someone to do something wonky in their environment and break it. :)
I've updated the check, and tested it on:
Windows 10 x64 Education (Build 17063) (Windows PowerShell)
Windows 10 x64 Education (Build 17063) (PowerShell Core 6.0.2)
Ubuntu 16.04 (PowerShell Core 6.0.2)
Windows Server 2008R2 SP1 (Windows PowerShell 2.0)

[rkeithhill]

LGTM

[TylerLeonhardt]

merge time 😎