How to View All Environment Variable and Their Values

Mac:

Open a terminal window and type printenv

~$ printenv

Windows (DOS):

Open a Command Prompt and type set

c:\Users\username? set

Windows (Powershell):

Open a Powershell window and type Get-Childitem env:

PS C:\Users\username> Get-Childitem env:               

Links
Mac/Unix Bash Shell
Dos
Powershell