#!/bin/sh
########################################################################
# pingDet.sh  Waits for next ping until count in command line or 
#             exit file (pingxit) no longer exists.
#             When ping arrives it exits, leaving status info on screen.
#             A line containing:
#             timestamp (followed by ".", characters "IP " are followed 
#             by the IP address of the sender which preceeds ">".
#             That information is then sent to all users via wall
#             The process repeats until command line count exceeded or xitping file removed.
########################################################################

svFil=/root/lstPng.dat

if [ "$LOGNAME" != "root" ]
then echo -e "\n\tError Must NOT be superuser."
     exit 1
fi

# If xitping non-existent then pingDet.sh exits
echo 0 > /root/xitping

# Sets max number of pings before exiting
ans=`echo $1 | grep -o "[a-zA-Z]"`
if [ "$ans" != "" ] 
then echo -e "\n\tERROR: Argument must be numeric"
     exit 1
fi

if [ $1 -le 30 ]
then max=$1
else echo -e "\n\tERROR: Argument must be 1-30"
     exit 1
fi

# Counter
k=0

# Infinit loop until count exceeded or pingxit vanishes.
while :
do
   k=`expr $k + 1`
# Restart tcpdump to write line to $svFil and exit on receipt of ping
# $svFile is also reused
   tcpdump -c 1 -A -i any -n 'icmp[icmptype] = icmp-echo' > $svFil

# Read line from $svFil
   read line < $svFil

# Save timestamp and source IP address
   tim=`echo $line | cut -d"." -f1`

   srcIP=`echo $line | cut -d"P" -f2-`
   srcIP=`echo $srcIP | cut -d">" -f1`

# Notify user
   wall -n << EOF
ATTENTION received PING #$k of $max at: $time from: $srcIP
EOF

# Exit forced by removing /root/xitping
   if [ ! -e /root/xitping ]
   then echo -e "\n\tpingDet exiting on NO xitping file-- RESTART"
        exit 1
   fi

# Exits after command line count
   if [ "$k" -ge $max ]
   then echo -e "\n\tpingDet exits on $max-th ping-- RESTART"
        exit 0
   fi
done