problem feeding netcat a list of hosts

Shell Programming and Scripting
1

Hi, I'm having difficulty in making a bash script to get netcat to scan a list of hosts and their ports from another file and could use some help. Here's an example host list, "nc.host":

192.168.2.110 22

And here's the first script I tried to feed "nc.host" into netcat:

"nc1.sh"

#!/bin/bash
for i in `cat nc.host`
do
nc -v $i
done

..... looks simple enough, but here's the error I get when I run the script:

[root@Dagobah test1]# ./nc1.sh
usage: nc [-46DdhklnrStUuvz] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]
usage: nc [-46DdhklnrStUuvz] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]

I got two usage errors right in a row. It's as if netcat is receiving the IP address and the port number as two separate arguments, and it doesn't know how to process the command "nc -v 192.168.2.110" or "nc -v 22". (Weird, I didn't tell the script to add an end- of- line to the IP address???) Maybe it's the single space between the IP and port in the nc.hosts file?

So I altered the script in the hopes of getting around the whitespace problem:

"nc2.sh"

#!/bin/bash
for i in `awk '{print $1" "$2}' nc.hosts`
do
nc -v $i
done

.. but I get the same two netcat ussage errors right in a row again!

I tried a shortcut way and it still fails:

[root@Dagobah test1]# awk '{print $1" "$2}' nc.host
192.168.2.110 22 #### it looks like it outputs right! =/

[root@Dagobah test1]# awk '{print $1" "$2}' nc.host | nc -v
usage: nc [-46DdhklnrStUuvz] [-i interval] [-p source_port]
[-s source_ip_address] [-T ToS] [-w timeout] [-X proxy_version]
[-x proxy_address[:port]] [hostname] [port[s]]

Any suggestions?

Thanks,
-Sean

2

Try this

while read host;do nc -z $host;done < nc.host

You should read the man page for your nc

3

OK, I tried the while/do and it worked, thank you very much. Now I have something new to work with.

FYI, I did read the man page (and other sources) before posting. Looking at the man page again I still don't see where it explains what I was looking for. The closest is the DATA TRANSFER section, but maybe barely hints at it.

At any rate, thank you for the help.

4

If you read carefully man nc you will see the difference between -v and -z .:wink: