How do you resolve special folders in path strings in PowerShell?

Question

In the Windows Command Prompt, special folders are resolved like so:

However, in powershell, these folders do not seem to be resolved:

Consider the string:

$myfile = "%temp%\\myfolder\\myfile.txt"

How can I use this as an argument to PowerShell functions (eg: Remove-Item ), and have PowerShell correctly resolve the special folders, as opposed to taking it literally and prepending the current working directory?

Edit:

I am working with strings using standard windows path notation coming from external configuration files, for example:

config.json:

{
    "some_file": "%TEMP%\\folder\\file.txt"
}

myscript.ps1:

$config = Get-Content -Raw -Path "config.json" | ConvertFrom-Json
Remove-Item -path $config.some_file -Force

Note: as any of the Windows special folders can appear in these strings, I'd rather avoid horrible find-replace hacks like this

$config.some_file = $config.some_file -replace '%TEMP%' $env:temp

Answer 1

If you don't mind some performance issues

$resolvedPathInABitHackyWay = (cmd /c echo "%TEMP%\\\\folder\\\\file.txt")

This will actually give you %TEMP% resolved by cmd itself.

Answer 2

You can grab all env variables from the env:\\ drive and use that to construct a succinct regex pattern for your find-replace operation, then use the Regex.Replace() method with a match evaluator:

$vars = Get-ChildItem env:\ |ForEach-Object {[regex]::Escape($_.Name)}
$find  = "%(?:$($envNames -join '|'))%"
[regex]::Replace($config.some_file, $find, {param([System.Text.RegularExpressions.Match]$found) return (Get-Item "env:\$($found.Groups[1])").Value},'IgnoreCase')

Answer 3

You can expand it to a full path using:

[System.Environment]::ExpandEnvironmentVariables("%TEMP%\\myfolder\\myfile.txt")

c:\users\username\AppData\Local\Temp\\myfolder\\myfile.txt

Double-backslash \\\\ isn't a PowerShell thing either, \\ is not a special character in a PowerShell string - but double backslashes in a path do seem to work.

Documentation: https://msdn.microsoft.com/en-us/library/system.environment.expandenvironmentvariables.aspx