global: not setting variables in functions in PowerShell

Question

So I have a personal project I'm working on where I want to set the value of $Name to the name of the script without the path or file extensions. I thought I could do this as a global variable since it needs to called a few times.

I've used the set-variable command and used $global:Name but nothing seems to work when I call the variable in the function. I've also used other variable names such as "foo" and it still wasn't working. Here are some example code snippets:

Set-Variable -name Name -value [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName) -scope global
function test {
    $Name
}
test
Pause

I've also tried:

Set-Variable -name Name -value [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName) -scope global
function test {
    $global:Name
}
test
Pause

And:

$global:Name = [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName)

function test {
    $Name
}
test
Pause

And:

$global:Name = [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName)
function test {
    $global:Name
}
test
Pause

And:

$script:Name = [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName)
function test {
    $script:Name
}
test
Pause

And:

$script:Name = [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName)
function test {
    $Name
}
test
Pause

I was expecting the name of the script to appear but it just returns null. Anyone know why this is happening? Any advice is much appreciated!

my understanding is that once you define a $Global: variable, you must always refer to it as such ... otherwise you will risk creating a new variable in the current scope. — Lee_Dailey
– Lee_Dailey, Commented Jul 17, 2019 at 22:59
Always using $global: is definitely the most robust way to refer to a global variable; specifically, it is assigning to a variable of the same name without the $global: scope in a non-global scope that creates a local variable that shadows the global one - see stackoverflow.com/a/54317129/45375 for the full story. — mklement0
– mklement0, Commented Jul 18, 2019 at 2:11
@Excallypurr, zdan's answer solves your problem, but as an aside: using Set-Variable means that argument-mode parsing is applied, so to use an expression such as [IO.Path]::GetFileNameWithoutExtension($MyInvocation.ScriptName) you need to enclose it in (...) - see stackoverflow.com/a/41254359/45375 — mklement0
– mklement0, Commented Jul 18, 2019 at 2:14

zdan · Accepted Answer · 2019-07-17 22:55:51Z

2

$MyInvocation does not provide information about the current script. It tells you about who called the script. As per the help:

Unlike the $PSScriptRoot and $PSCommandPath automatic variables, the PSScriptRoot and PSCommandPath properties of the $MyInvocation automatic variable contain information about the invoker or calling script, not the current script.

So what you want to use is $PSCommandPath, like this:

$global:Name = [IO.Path]::GetFileNameWithoutExtension($PSCommandPath)
function test {
    $Name
}
test

answered Jul 17, 2019 at 22:55

zdan

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