Using variable as parameter works, using source of variable fails

Question

I found a way to get the current working directory into $dp0.

PS C:\src\powershell> Get-Content .\curdir2.ps1
$dp0 = [System.IO.Path]::GetDirectoryName($myInvocation.MyCommand.Definition)

Set-Location -Path $dp0
Write-Host "location is set"

Set-Location -Path [System.IO.Path]::GetDirectoryName($myInvocation.MyCommand.Definition)

Write-Host (Get-Location).Path

Why is it that when I try to use the same way as a parameter to Set-Location it is an error? I think this may be something fundamental about the objects in Powershell. What do I need to know?

Set-Location : A positional parameter cannot be found that accepts argument 'C:\src\powershell\curdir2.ps1'.
At C:\src\powershell\curdir2.ps1:6 char:1
+ Set-Location -Path [System.IO.Path]::GetDirectoryName($myInvocation.MyCommand.De ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [Set-Location], ParameterBindingException
    + FullyQualifiedErrorId : PositionalParameterNotFound,Microsoft.PowerShell.Commands.SetLocationCommand

woxxom · Accepted Answer · 2016-08-31 13:54:06Z

2

Use parentheses.
As you can see in PS ISE that entire parameter is interpreted as a literal string otherwise.
And always use -LiteralPath instead of -Path to correctly handle directories with [] brackets.

Set-Location -LiteralPath ([IO.Path]::GetDirectoryName($myInvocation.MyCommand.Definition))

PS3.0+: cd -LiteralPath $PSScriptRoot

answered Aug 31, 2016 at 13:54

woxxom

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2 Comments

lit Over a year ago

I am giving you the check mark. Can you say anything more about why parentheses are needed? I do not think I have ever seen that in other languages.

woxxom Over a year ago

PowerShell syntax is quite weird because it treats unquoted text as strings for parameters of string and string[] (array of strings) types. And just like inside a string it only recognizes the variables $var and expressions $(....). Bare parentheses are basically a shorthand of the latter when no quotes are used.

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