#! /bin/sh
#
###	motd.diff - show changes (additions) to /etc/motd (message of day)
###	Usage: motd.diff
##
##	motd.diff IS HANDY IF YOU TEND TO IGNORE YOUR SYSTEM MESSAGES
##	(motd FILE) WHEN YOU LOG IN; motd.diff WILL BE SURE YOU SEE ANY
##	NEW MESSAGES.
##
##	IF YOU RUN motd.diff FROM YOUR .login OR .profile FILES, IT WILL
##	WATCH THE SYSTEM MESSAGE-OF-THE-DAY FILE, /etc/motd.
##	IF THE MESSAGE HASN'T CHANGED SINCE THE LAST TIME YOU LOGGED IN,
##	OR IF PART OF THE MESSAGE HAS BEEN DELETED, motd.diff WON'T SHOW
##	ANYTHING.  OTHERWISE, motd.diff WILL SHOW YOU ANY LINES THAT HAVE
##	BEEN ADDED TO THE FILE (THESE ARE USUALLY NEW NOTICES).
##
##	AFTER SHOWING YOU THE NEW MESSAGES, motd.diff WILL WAIT FOR YOU
##	TO PRESS THE RETURN KEY.  THIS KEEPS MESSAGES FROM SCROLLING
##	OFF THE SCREEN BEFORE YOU READ THEM.  (NOTE: IT WON'T WAIT IF
##	THE STANDARD INPUT IS NOT A TERMINAL -- IF YOU'RE RUNNING IT FROM
##	AN at JOB, FOR INSTANCE.)
##
##	(THIS PROGRAM KEEPS A FILE NAMED .motd.diff.$HOST IN YOUR HOME
##	DIRECTORY; IT HOLDS THE MOST-RECENT VERSION OF motd FILE FOR YOUR
##	CURRENT HOST, WHERE $HOST IS THE HOSTNAME.)

# IF $HOME NOT SET, BARF AND EXIT:
: ${HOME?"cannot find in your environment; quitting"}

temp=/tmp/MOTD.DIFF$$

# UNCOMMENT THE RIGHT LINE FOR YOUR UNIX:
# echo="echo -n" nnl= 	# BSD
# echo=echo      nnl="\c"	# SYSV
echo="echo -n" nnl= 	PATH=/usr/bin:$PATH; export PATH	# SunOS

# GET BASENAME OF HOSTNAME; USE IN FILE EXTENSION
# SO THAT NETWORKED MACHINES WHICH ALL USE THE SAME HOME DIRECTORY
# WILL HAVE DIFFERENT .motd.diff FILES:
hostname="`expr \`hostname\` : '\([^.]*\).*'`"
lastmotd=$HOME/.last.motd.$hostname

>> $lastmotd	# BE SURE $lastmotd EXISTS SO diff WON'T BOMB
trap 'rm -f $temp; exit' 0 1 2 15

if diff $lastmotd /etc/motd > $temp
then :
else
	if grep "^>" $temp >/dev/null	# diff USES > TO MARK NEW LINES
	then
		echo "Additions to system message-of-the-day:"
		# ONLY PRINT LINES WHICH HAD A '>' AT THE START
		# (REMOVE THE '> ' FIRST):
		sed -n -e 's/^> //p' $temp | more
		# IF USER IS USING A TERMINAL, WAIT FOR A <RETURN>:
		if test -t 0
		then
			$echo "Hit RETURN to continue: $nnl"
			read dummy
		fi
	fi
	cat /etc/motd > $lastmotd	# cp MAY SCREW UP FILE MODE
fi