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From: ado@elsie.UUCP (Arthur David Olson)
Newsgroups: net.unix-wizards
Subject: Re: Re: mailwatch script wanted
Message-ID: <5196@elsie.UUCP>
Date: Tue, 30-Jul-85 21:45:18 EDT
Article-I.D.: elsie.5196
Posted: Tue Jul 30 21:45:18 1985
Date-Received: Thu, 1-Aug-85 06:21:27 EDT
References: <411@sdcc12.UUCP> <319@tektools.UUCP> <160@kitty.UUCP> <2509@sun.uucp>
Organization: NIH-LEC, Bethesda, MD
Lines: 25
Summary: odd use for the set-user-ID bit

> . . .they should have added a flag which tells "mail" to *print* a message
> . . .or to return one of *three* exit statuses.  That way, you can distinguish
> "You have mail (because you leave stuff around in your mailbox until you've
> responded to it)" from "You have mail (because some mail arrived since the
> last time you looked at your mailbox).")

For those running 4.?bsd and using the C shell, here's an odd way to do pull off
the second trick.  Add this line to your ".cshrc" file
	alias mail '/usr/ucb/mail \!* ; if ( "\!*" == "" ) chmod u+s $mail'
(substituting for "/usr/ucb/mail" as appropriate) and this line to your
".login" file
	find $mail \! -perm -4000 -exec echo "You have new mail." \;
(ensuring that "$mail" gets set before this point in the ".login" file).

Given the alias, the set-user-id bit of your mail file will be set each time
you read your mail.  Given the way 4.?bsd works, the set-user-id bit is cleared
each time mail is written to your file.  The "find" command simply checks the
bit to determine whether or not you have "new" mail.
--
UNIX is an AT&T Bell Laboratories trademark.
Sun is a Sun Microsystems trademark.
An AT&T employee holds a patent on the set-user-ID bit.
--
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