If you use Linux or another UNIX-like operating system and find yourself forgetting exactly which $ prefixed command does what, this is for you:
-
$$– the PID of the current process -
$!– the PID of the most recent background process -
$?– the most recent exit code -
$#– the number of passed parameters -
$*/$@– a string / array of the passed parameters -
$_– the most recent parameter -
$0– script/program name (0th parameter) -
$1…$9– positional parameters 1 through 9 -
$NAME– references environment variable “NAME”
