portScanner.sh

#!/bin/bash
#
# Thi is a simple IP and Port Scanner for the Bash.
#
# Performs a ping sweep over each Host o a Subnet (1..254). 

# If a Host is on, then the Port TCP 53 (DNS) is checked.

# TO BE DONE: add other interesting Ports (80, 8080, 69, 20, 21, 22...). 

# Boh may work against a Linux device (because of echo > /dev/tcp...).

network="192.168.1."
port=53
for host in {1..254}; do
	ping -c 1 $network$host &> /dev/null 
	[ $? -eq 1 ] && continue 
	(echo > /dev/tcp/$network$host/$port) &>/dev/null
	[ $? -eq 0 ] && [ $port -eq 53 ] && echo "$network$host DNS Server"	
done


# --------------------------------------- NOTES:---------------------------------------
# $? identifies the exit status of the last executed command 
# "0" stands for true
# "1" stands for false
# 
# On line 15 you can see that, if the ping command has no success, 
# the execution continues to the next iteration (then, "continue" is a sort of a jumper).
# 
# With regard to line 16 remember that, when executing a command on a /dev/tcp/$host/$port 
# pseudo-device file, Bash opens a TCP connection to the associated socket.