Summary: Learn a one-liner Windows PowerShell command to see how long a computer has run.

 How can I use Windows PowerShell to find out how long my computer has been running
          since last boot up without writing a script?

 Use the Win32_OperatingSystem WMI class and the LastBootupTime property,
          and then subtract the value of the current date/time that comes from Get-Date:

(Get-Date) – (Get-CimInstance Win32_operatingSystem).lastbootuptime