Use this command to see a list of all the variables available

[Environment]::GetEnvironmentVariables()

Here is an example to get the machine variable

[Environment]::GetEnvironmentVariables("Machine")

Here is an example to get two variables, Temp and User

[Environment]::GetEnvironmentVariable("Temp","User")

In this example you can see how to connect to a computer to get a variable remotely

Invoke-Command -ComputerName $Target -ScriptBlock { $COMMAND } -Credential $USERNAME

Temp directory path for user Bob on remote machine

Invoke-Command -ComputerName "Computername" -ScriptBlock {[Environment]::GetEnvironmentVariable(“Temp”,”User”)} -Credential Bob

Reference:

Get list of environment variables from Powershell