CODEWITHSUNDEEP
bashfilternetcat
Tubby Tommy
Tubby Tommy

Reputation: 31

Filtering Netcat results in a Bash script

I am trying to write a script that connects to a list of IPs on port 53 - and I want the result to return only open ports. Here is the script I am running below - I have tried grepping and cutting the output but im not sure I am doing this correctly - I cant seem to pipe the script results to a text file either.

#!/bin/bash

for ip in $(seq 200 254); do
    nc -v 192.168.11.$ip 53 &
done

I apologise for its simplicity I am new - and if the solution is elsewhere

Upvotes: 1

Views: 2898

Answers (2)

Peter Oram
Peter Oram

Reputation: 6768

If you want all the output of a command to go to a file use &>. In your example you could use:

#!/bin/bash

for ip in $(seq 200 254); do
    nc -v 192.168.11.$ip 53 &>> myFile
done

Then you can manipulate (grep, sed, awk, etc.) myFile however you want.

Upvotes: 0

Igor Pozgaj
Igor Pozgaj

Reputation: 199

Check for the command's exit code, it should be zero for a successful connection. Also use the -z option to drop the connection once it has been established.

#!/bin/bash

for ip in $(seq 200 254); do
    nc -z 192.168.11.$ip 53
    if [ $? -eq 0 ]; then
        echo "Hit: 192.168.11.$ip"
    fi
done

If you were using nmap instead of netcat, you could have used this:

nmap 192.168.11.200-254 -p 53

PS. If you're trying to determine which hosts run DNS server, you should scan for open 53/udp, not 53/tcp (option -u in netcat)

Upvotes: 2

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