I have crafted a Bash tool that runs on a server. This tool will block certain IP addresses for a certain time range (i.e. from 5 A.M. to 3:30 P.M.).
As of currently, the tool works fine, but I have to input IP addresses to certain websites manually into a text file and have the tool pull the IP address based on the nth line using the "head" and "tail" commands. I don't want to do this as I believe a single ping will be much more lightweight and portable. So if I do a ping for Google:
ping google.com -c 1 -s 16
The output will be:
Ubuntu@yokai:~# ping google.com -c 1 -s 16
PING google.com (173.194.66.138) 16(44) bytes of data.
24 bytes from qo-in-f138.1e100.net (173.194.66.138): icmp_seq=1 ttl=37 time=46.7 ms
--- google.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 46.748/46.748/46.748/0.000 ms
And the command I have narrowed this output down with is:
ping google.com -c 1 -s 16 | grep -o '([^ ]*' | tr -d '(44):\n'
Which gives me an output of:
173.19.66.113173.19.66.113ubuntu@yokai
As you can see, there is a duplicate of the same IP address. How can I remove the duplicate with sed so that I can store the single IP address into a variable and run the script as a cronjob, or am I on a better track using tr?
(EDIT)
I already know/knew how to resolve IP address from a host name or domain. That is not what I am asking here. This question is specifically about managing ping output using sed in order to keep the tool I have created more portable as ping comes default with almost any and all linux distros.
(UPDATE) Since some marked this question a duplicate of some other bullshit question that has nothing to do with this one, I will make it clear enough that retards with English comprehension troubles can understand:
How to parse the IP ADDRESS "ONLY" from ping OUTPUT when using ping on a domain name.
This is NOT asking to resolve a domain name and therefore is NOT A DUPLICATE!!!
(LATEST UPDATE) I have, since asking this question, learned proper POSIX regex to do what I needed and I need to make it clear that I was originally asking about the regular expressions for sed that would print a single instance of an IP from ping output. I have since refined my methods and do not use any of the answers here but I thank everyone for their attempts with helping here. I am now using a timer script that I created to configure iptables at certain times to block certain domain name resolutions. Again, thank you to everyone that tried to help.
ping is for checking whether a host is up or down based on ICMP response, it is never the right tool for only resolving IP address, there are dedicated tools for that.
You should look at dig, host, nslookup -- whatever suites you the best.
Here's a dig output:
% dig +short google.com
123.108.243.57
123.108.243.51
123.108.243.54
123.108.243.48
123.108.243.60
123.108.243.52
123.108.243.56
123.108.243.55
123.108.243.61
123.108.243.58
123.108.243.49
123.108.243.50
123.108.243.59
123.108.243.47
123.108.243.53
As a side note, in Linux, if you want to query by the NSSwitch (Name Service Switch) i.e. /etc/nsswitch, then use the getent command with hosts (or ahosts) database e.g.:
getent hosts google.com
In my computer, i have:
hosts: files mdns4 dns
in /etc/nsswitch.conf, so getent hosts will query in sequence and use gethostbyaddr(3) or gethostbyname(3) based on name and ahosts will use getaddrinfo(3).
In essence, with my configuration, this will first check /etc/hosts, then mDNS and at last DNS.
If you insist on using ping and sed, you can do:
% ping -c1 google.com | sed -nE 's/^PING[^(]+\(([^)]+)\).*/\1/p'
123.108.243.56
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