Please refer the below script to, Get List of Environmental Variables.
Environment variables work like placeholder or alias for drives, file/folder names and various paths.
This script will display the information of
TMP ,COMPUTERNAME ,USERDOMAIN, PSMODULE,PATH, COMMONPROGRAMFILES, PROCESSOR_IDENTIFIER, PROGRAMFILES, SYSTEMROOT, PATHPROGRAMFILES(X86), COMSPECPROGRAMDATA, APPDATA, COMMONPROGRAMW6432, OS and other etc.
Please run the script procedure as either "system user" or Loggedinuser.