Forums Scripts & Popups on join send message and log user ???

I know there is a way to make an on join message but is there a way after sending the message that it logs the name so it will NOT send them that message next time they join?

Example
bob joins #chan1
<mybot> hello bob if you need help with bots type !help and I will private message you the bots commands ***This is a one time message but you can use !help at any time***
jane joins #chan1
<mybot> hello jane if you need help with bots type !help and I will private message you the bots commands ***This is a one time message but you can use !help at any time***
Bob left #chan1
2 days later bob joins but the bot knows he was sent the message already so does not send the message.

any idea? also I would like to manually add people that already know the commands and do not need to get this message