PowerShell script/function that invokes a command with a temporarily modified environment.

Invoke-WithEnvironment.ps1

function Invoke-WithEnvironment {
<#
.SYNOPSIS
Invokes commands with a temporarily modified environment.

.DESCRIPTION
Modifies environment variables temporarily based on a hashtable of values,
invokes the specified script block, then restores the previous environment.

.PARAMETER Environment
A hashtable that defines the temporary environment-variable values.
Assign $null to (temporarily) remove an environment variable that is
currently set.

.PARAMETER ScriptBlock
The command(s) to execute with the temporarily modified environment.

.EXAMPLE
Invoke-WithEnvironment @{ PORT=8080 } { node index.js }

Runs node with environment variable PORT temporarily set to 8080, with its
previous value, if any, restored afterwards.
#>
  param(
    [Parameter(Mandatory)] [System.Collections.IDictionary] $Environment,
    [Parameter(Mandatory)] [scriptblock] $ScriptBlock
  )
  # Modify the environment based on the hashtable and save the original
  # one for later restoration.
  $htOrgEnv = @{}
  foreach ($kv in $Environment.GetEnumerator()) {
    $htOrgEnv[$kv.Key] = (Get-Item -EA SilentlyContinue "env:$($kv.Key)").Value
    Set-Item "env:$($kv.Key)" $kv.Value
  }
  # Invoke the script block
  try {
    & $ScriptBlock
  } finally {
    # Restore the original environment.
    foreach ($kv in $Environment.GetEnumerator()) {
      # Note: setting an environment var. to $null or '' *removes* it.
      Set-Item "env:$($kv.Key)" $htOrgEnv[$kv.Key]
    }
  }
}

# -- Generic code that handles the invocation.
if ($MyInvocation.InvocationName -eq '.' -or $MyInvocation.Line -eq '') { # Being dot-sourced
  if ($MyInvocation.Line -eq '' -and $host.Name -eq 'Visual Studio Code Host') { # Support for debugging in VSCode
      # If the current file is directly launched for debugging from the editor, 
      # use a custom invocation with arguments for debugging.
      Write-Warning 'VSCode debugging: Invoking embedded function with custom arguments.'
      & ([System.IO.Path]::GetFileNameWithoutExtension($PSCommandPath)) # Add arguments for debugging here.
  } else {
    # Nothing further to do: the function has been defined in the current scope for *later* use.
    # However, we warn if arguments were unexpectedly passed or something is being piped.
    if ($Args.Count -or $MyInvocation.ExpectingInput) { Write-Warning "Ignoring arguments and/or pipeline input due to being dot-sourced: $PSCommandPath" }
  }
} else { # Script is invoked directly (by name/path directly or via &)
  # Call the embedded function of the same name, relaying any arguments passed.
  if ($MyInvocation.ExpectingInput) { # pipeline input present
    $Input | & ([System.IO.Path]::GetFileNameWithoutExtension($PSCommandPath)) @Args
  } else { # only arguments, if any
    & ([System.IO.Path]::GetFileNameWithoutExtension($PSCommandPath)) @Args
  }
}