Is a .ps1 script being run from PShell or PowerShell 5.1?

$IsPshell = $true

try {
    $null = [TakeCommand.PowerShellHost]::ExpandValue('%_cwd')
}
catch {
    $IsPshell = $false
}

if ($IsPshell) {
    # PSHELL-only callbacks
    $cwd = [TakeCommand.PowerShellHost]::ExpandValue('%_cwd')
    Write-Host "PSHELL cwd: $cwd"
} else {
    Write-Host "Running under PowerShell 5.1"
}