As other stackoverflower's said, I would recommend using nmap
or netcat
if avilable.
However, if you cannot use those software, you can use bash's builtin /dev/tcp/<host>/<port>
instead.
http://www.gnu.org/software/bash/manual/bashref.html#Redirections
I could'nt figure out which version of bash you are using, but /dev/tcp/...
seems to implemented since some old bash.
#!/bin/bash
echo "scanme.nmap.org 21
scanme.nmap.org 22
scanme.nmap.org 23
scanme.nmap.org 79
scanme.nmap.org 80
scanme.nmap.org 81" | \
while read host port; do
r=$(bash -c 'exec 3<> /dev/tcp/'$host'/'$port';echo $?' 2>/dev/null)
if [ "$r" = "0" ]; then
echo $host $port is open
else
echo $host $port is closed
fi
done
This produces
scanme.nmap.org 21 is closed
scanme.nmap.org 22 is open
scanme.nmap.org 23 is closed
scanme.nmap.org 79 is closed
scanme.nmap.org 80 is open
scanme.nmap.org 81 is closed
UPDATED: The following can do timeout. Although it may seem little tricky, idea is just to kill the child process after some timeout.
Bash script that kills a child process after a given timeout
#!/bin/bash
echo "scanme.nmap.org 80
scanme.nmap.org 81
192.168.0.100 1" | (
TCP_TIMEOUT=3
while read host port; do
(CURPID=$BASHPID;
(sleep $TCP_TIMEOUT;kill $CURPID) &
exec 3<> /dev/tcp/$host/$port
) 2>/dev/null
case $? in
0)
echo $host $port is open;;
1)
echo $host $port is closed;;
143) # killed by SIGTERM
echo $host $port timeouted;;
esac
done
) 2>/dev/null # avoid bash message "Terminated ..."
this produces
scanme.nmap.org 80 is open
scanme.nmap.org 81 is closed
192.168.0.100 1 timeouted
since 192.168.100 does not exist in my local network.