#!/bin/sh
### This simple script monitors the state of a network ###

# Configuration variables
CHECK_ADDR="www.yahoo.com"
CHECK_CMD="ping -c1 -w2 $CHECK_ADDR"
OUTAGE_CMD="echo NETWORK OUTAGE DETECTED AT $(date)"
OUTAGE_WAIT=0
RESTORE_CMD="echo NETWORK RESTORE DETECTED AT $(date)"
RESTORE_WAIT=0

# This function does nothing until $CHECK_CMD fails.
# When that happens, $OUTAGE_CMD runs and the function exits
check_for_outage() 
{	
	$CHECK_CMD &> /dev/null
	while [ $? -eq 0 ]
	do
		sleep $OUTAGE_WAIT
		$CHECK_CMD &> /dev/null
	done
	$OUTAGE_CMD
}

# This function is the same as check_for_outage but it waits for $CHECK_CMD to succeed.
# When that happens, $RESTORE_CMD runs and the function exits
check_for_restore()
{
	$CHECK_CMD &> /dev/null
	while [ $? -ne 0 ]
	do
		sleep $RESTORE_WAIT
		$CHECK_CMD &> /dev/null 
	done
	$RESTORE_CMD 
}

# This function loops forever, alternating between checking to see if the net is down
# and checking to see if it's back up again. 
while [ 1 -eq 1 ]
do
	check_for_outage
	check_for_restore
done