function Get-Uptime {
    [CmdletBinding()]
    [OutputType([string])]
    param (
    )

    if (Test-IsWindowsPlatform) {
        $now = Get-Date
        $lastStartTime = (Get-CimInstance -ClassName Win32_OperatingSystem).LastBootUpTime

        $uptime = $now - $lastStartTime

        return $uptime.ToString()
    } else {
        return "we clobbered the system uptime, doh"
    }
}

Set-Alias -Name uptime -Value Get-Uptime