guessmypi

#!/bin/bash
SNAME=$(uname -s)

# Assume a default interface.  eth0 isn't so predictable on linux anymore, TODO a better one there.

case $SNAME in
	"Darwin")	IFACE=${1-en0};;
	"Linux")	IFACE=${1-eth0};;
	*)			echo Sorry, I was too lazy to add your OS; exit 1;;
esac

# pull my own LL address from ifconfig.  by OS again because ifconfig has slightly different format.

case $SNAME in
	"Darwin")	MYSELF=$(ifconfig $IFACE | grep fe80 | awk '{print $2}' | sed 's|%.*||');;
	"Linux")	MYSELF=$(ifconfig $IFACE | grep fe80 | awk '{print $3}' | sed 's|/.*||');;
esac

# Sanity check

if [ -z "$MYSELF" ]; then
	echo Could not determin own linklocal address.
	exit 1
fi

# ping v6 broadcast (ff02::1) and remove myself from the reults.
# -c 3 because for a single ping, ping stops listening after the first return, which is usually the local machine

BCAST=ff02::1

case $SNAME in
	#		    broadcast ping			 | ..bytes from	|      cut times	|  tidy up	| remove myself		| and output
	"Darwin")	NEIGHBOURS=$(ping6 -c 3 -I $IFACE $BCAST | grep ^16	| sed 's|%.*||' 	| sort|uniq 	| grep -v $MYSELF	| awk '{print $4}');;
	"Linux")	NEIGHBOURS=$(ping6 -c 3 -I $IFACE $BCAST | grep ^64	| sed 's|: .*||'	| sort|uniq 	| grep -v $MYSELF	| awk '{print $4}');;
esac

# now we're getting somewhere!

NDCOUNT=$(echo $NEIGHBOURS | wc -w | tr -d " ")		# count results
if [ $NDCOUNT -eq 1 ]; then
	ssh pi@$NEIGHBOURS%$IFACE			# do eeet
else
	echo Could not guess, $NDCOUNT neighbours	# or not
	exit 1
fi