Argument as variable, instead of directly passing file path, to PowerShell cmdlets

Question

I store file path in variable as below

$body = E:\Folder\body.txt

And try to access it at multiple areas in a PowerShell script like below

Clear-content -$body

Get-content $body.ToString()

Set-content $body

But all these three type of passing arguments are not working. I am getting errors below.

Cannot find path 'C:\Users\S51\-' because it does not exist

You cannot call a method on a null-valued expression

Cannot bind argument to parameter 'Path' because it is null

Only the traditional

Clear/Get/Set-content E:\Folder\body.txt methods work.

Is there any way to assign path to a variable and use them across whole code because I need to access the same path multiple times & if I need to modify the file path in future it requires to modify everywhere. If it is a variable, I can just modify at one place.

Not sure, but I think you want to have a look at Scopes. Possiby, you want to declare the path variable as $global:ThePathVariable — Theo
– Theo, Commented May 9, 2020 at 8:40
For a start, it's not seeing your filepath - you should use Clear-Content -Path $body and yes, if it;s using a differnt path then you probably need to define $body with a wider scope e.g. $Script:body = E:\Folder\body.txt — Scepticalist
– Scepticalist, Commented May 9, 2020 at 8:50

Community · Accepted Answer · 2020-06-20 09:12:55Z

tl;dr

Your symptoms are all explained by the value of $body effectively being $null.
The problem is that E:\Folder\body.txt isn't quoted; if you quote it, your symptoms go away:

$body = 'E:\Folder\body.txt'

The bottom section of this answer explains string literals in PowerShell, and this answer explains PowerShell's two fundamental parsing modes, argument (command) mode and expression mode.

Explanation:

I store file path in variable as below

$body = E:\Folder\body.txt

Because what you intend to be string E:\Folder\body.txt isn't quoted, E:\Folder\body.txt is interpreted as a command, which means:

E:\Folder\body.txt is opened as a document, which means that it is opened asynchronously in Notepad.exe by default.
Since this operation has no output (return value), variable $body is created with value $null (strictly speaking, the [System.Management.Automation.Internal.AutomationNull]::Value value, which in most contexts behaves like $null).

All your symptoms are the result of the value of $body effectively being $null.

derekbaker783 · Accepted Answer · 2020-05-09 10:41:14Z

0

The code below illustrates several ways of using a variable to operate on files.

param(
    [string] $body = "$PSScriptRoot\body.txt"    
)

if ((Test-Path -Path $body) -eq $false) {
    New-Item -Path $body -ItemType File
}

function GetContent() {
    Get-Content -Path $body -Verbose
}
GetContent

function GetContentOfFile([string] $filePath) {
    Get-Content -Path $body -Verbose
}
GetContentOfFile -filePath $body

Invoke-Command -ScriptBlock { Clear-Content -Path $body -Verbose }

Invoke-Command -ScriptBlock { param($filepath) Clear-Content -Path $filepath -Verbose } -ArgumentList $body

Set-content -Path $body -Value 'Some content.' -Verbose

answered May 9, 2020 at 10:41

derekbaker783

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