PowerShell Error - Missing expression after unary operator '-' - powershell

Question

I have two PowerShell scripts. One is for uninstalling and installing a SharePoint 2010 solution on the SharePoint server. The other calls this script with two commands, one for the uninstall and one for the install. These are not scripts I wrote, but I have inherited them.
Here is the script that calls the install / uninstall script (I've removed some parameters to simplify for troubleshooting):
& 'C:\Users\username\Documents\setup.ps1' -InstallOrUninstall '/UNINSTALL'
& 'C:\Users\username\Documents\setup.ps1' -InstallOrUninstall '/INSTALL'
Stripped down to almost nothing for the purpose of testing, here is the "setup.ps1" script:
param ($InstallOrUninstall,
$SiteURL,
$WebURL,
[switch]$ignoreFeatures,
[switch]$thisAppDomain )
if (-not $thisAppDomain)
{
Write-Host "Invoking script in a new app domain" -foregroundcolor yellow
Write-Host $MyInvocation.Line
powershell.exe -Version 2 -Command $MyInvocation.Line -thisAppDomain
return;
}
Write-Host "In Body"
Write-Host $MyInvocation.Line
Running the first script returns an error from the first command, but not from the second. The error is:
powershell.exe : - : Missing expression after unary operator '-'.
At C:\Users\username\Documents\setup.ps1:11 char:6
+ powershell.exe -Version 2 -Command $MyInvocation.Line -thisAppDo ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (- : Missing exp...y operator '-'.:String) [], RemoteException
+ FullyQualifiedErrorId : NativeCommandError
+ CategoryInfo : ParserError: (-:String) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : MissingExpressionAfterOperator
I believe the reason the install / uninstall script is resending the command for "Version 2" is because of an issue with using PowerShell past Version 2 with SharePoint 2010 (as outlined here). However, I don't understand why only the first line fails. The second command also enters the if statement, but does not error.
If I remove the second line, and only call the setup.ps1 one time, the script that calls the install / uninstall script succeeds.

Answer 1

A nice little brain-teaser. Apparently, $MyInvocation.Line contains the full line, including the newline / linebreak at the end. So, -thisAppDomain is not interpreted as a parameter, but the beginning of a new expression starting with -. This is also, why it works if you remove the 2nd line, because then you do not have a line break at the end.
To reproduce this error, try:
powershell.exe -Version 2 -Command "`r`n-thisAppDomain"
Note that in newer versions the parsing algorithm was obviousy modified and the error message is different. Omit the -Version 2 switch and you likely get:
The term "-thisAppDomain" is not recognized as the name of a cmdlet, function, script file, or operable program...
One simple way to resolve this would be to .Trim() (or .TrimEnd()) the command:
powershell.exe -Version 2 -Command $MyInvocation.Line.Trim() -thisAppDomain
I need to add though, that you should reconsider what your actual problem is, and if your solution is actually the best way to solve it. Have a look at jobs for example.

Answer 2

As marsze said: It is not interpreted as a parameter, but the beginning of a new expression starting with -. This is also, why it works if you remove the 2nd line, because then you do not have a line break at the end.