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Just starting to learn some bash scripting, and I'm having trouble understanding how the redirection operators work. I wrote a very simple bash script, where I run a netcat port scan against a text file, which contains a list of hosts (not very practical, but just messing around with it), and I can't get it to send the output to a text file. The text file itself gets created, but there is no data in it. Here's what my script looks like:
for ip in $(cat ips.txt); do
nc -vv -z $ip 1-100 > results.txt
I'm sure it's a simple fix, but something isn't clicking in my head. Can anyone offer some pointers?
Lets check its working; I used my local IP addr to test and got plenty of output.
I noticed that if you re-direct to a file, only successful cxns ie open ports are written to stdout; failures go to stderr.
To collect even those
So, the script is still a bit flaky acting. While it was running against the list of IP's, it would update the nc.out file, but then it would zero itself out, and start over. When the script finished, the only data that was in the nc.out file, was the last host that was scanned.
Is there a better way to write this script, than what I have?