I have been studying for my Unix exam and I often saw exclamation mark variable -
If I write
echo $! on my Mac shell tells me something like "You have mail in…"
Is purpose of this to store whether I do or do not have any mails or is there something else?
EDIT: Funny coincidence happened. Exactly when I wrote
echo $! my Shell also notified me that I have some mail. So that's why I wrote that mail part.