Been a few days of learning since I last wrote one of these, but I have come back to the automatic variables page on the PowerShell documentation enough times that I think I should just blog the important parts for myself.
$?– TRUE/FALSE if the last thing you did succeeded.
$_– Something everyone uses in posh, current pipeline object.
$Args– all the undeclared params passed to a function, try to avoid.
$Error– the array of error objects that represent a stack of the most recent errors. use $Errors0 to get the most recent error.
Read on for more variables.