Take the 2-minute tour ×
Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems.. It's 100% free, no registration required.

Is there an easy way to programmatically extract IP address, without tedious parsing of ifconfig? I would not mind simple command output processing using sed to do it but not processing multiline files from /etc some place. What I am trying to do is modify my .bashrc to display the IP address of the host in the greeting message. I am using Ubuntu 12.04 but decided to post here instead of the Ubuntu forum because I consider this to be not distro-specific.

share|improve this question
1  
hosts have IP (v4 or v6) addresses on each of the IP networks they're connected to. For instance, most host have a 127.0.0.1 IPv4 address and a ::1 IPv6 interface on the loopback network. Which one do you want to find? –  Stéphane Chazelas Aug 20 '13 at 16:11
    
the one in the eth0 section on ifconfig that is labeled inet addr: –  amphibient Aug 20 '13 at 16:15
    
I assume you want your private address, not your public one? –  strugee Aug 20 '13 at 23:09
    
yes, @strugee, that is correct –  amphibient Aug 21 '13 at 1:31

2 Answers 2

up vote 15 down vote accepted

NOTES

  1. NIC device handles

    The examples below assume that the network interface is a wireless card named wlan0. Adjust this bit in the examples for your particular situation. For example if it's a wired NIC card, then it's likely eth0.

  2. IPv4 - (Internet Protocol version 4)

    Also these examples are returning the IPv4 address. the "dotted quad" that most people identify as their "IP Address".

    For example:

    inet addr:192.168.1.20  Bcast:192.168.1.255  Mask:255.255.255.0
    
  3. IPv6 - (Internet Protocol version 6)

    If your system is configured to support IPv6 you'll see both the "dotted quad" as well as the IPv6 IP addresses in the ifconfig output.

    For example:

    inet6 addr: fe80::226:c7ff:fe85:a720/64 Scope:Link
    

    The commands below explicitly ignore this, but could be adapted quite easily to grab this information instead.

Solutions (using ifconfig)

There are many ways to do this. You could for example use this awk script to parse out the IP address of your wireless LAN NIC (wlan0):

$ ifconfig wlan0 | grep "inet " | awk -F'[: ]+' '{ print $4 }'
192.168.1.20

You can do this and make it more compact:

$ ifconfig wlan0 | awk '/t addr:/{gsub(/.*:/,"",$2);print$2}'
192.168.1.20

You could also do it using perl:

$ ifconfig wlan0 | perl -nle'/t addr:(\S+)/&&print$1'
192.168.1.20

The Perl example is about as compact as it can get.

There are countless other ways to do this, these are just a couple of examples to get you started.

EDIT #1

Some additional notes and comments. @StephaneChazelas demonstrated that there is an even more compact version using grep:

$ ifconfig wlan0|grep -Po 't addr:\K[\d.]+'
192.168.1.20

This solution makes use of grep's ability in newer versions to make use of PCRE (Perl regular expressions), along with it's -o switch to return just what matches the regular expression.

Solutions (using ip)

As was also mentioned in the comments, ifconfig can be troublesome to use on systems that have multiple IP addresses assigned to a network device, given it only returns the first one. So it's better to use the command ip in these situations.

For example:

$ ip addr show wlan0 | grep -Po 'inet \K[\d.]+'
192.168.1.20

You can also tell ip to only show you IPv4 information for a given network interface. In this case we're looking only at the interface named wlan0:

$ ip -f inet addr show wlan0 | grep -Po 'inet \K[\d.]+'
192.168.1.20

References

share|improve this answer
    
PERFECT !! I just replaced your wlan0 with eth0 and got the IP address –  amphibient Aug 20 '13 at 16:24
2  
@amphibient - glad to hear it solved your problem. Thanks for the question. –  slm Aug 20 '13 at 16:28
3  
Note that it returns the first IPv4 address of the interface. Interfaces can have more than one IP address. You need ip addr show to see all of them as ifconfig only shows one of them. –  Stéphane Chazelas Aug 20 '13 at 16:44
2  
Shorter with GNU grep: ifconfig eth0|grep -Po 't addr:\K[\d.]+' which has the advantage of returning a non-zero exit status if the interface has no address. –  Stéphane Chazelas Aug 20 '13 at 16:46
    
@StephaneChazelas - remind me to never play golf with you 8-) –  slm Aug 20 '13 at 17:05

$ hostname -I

For example:

$ hostname -I
192.168.1.18

Info. from manpages:

http://manpages.ubuntu.com/manpages/raring/en/man1/hostname.1.html
http://unixhelp.ed.ac.uk/CGI/man-cgi?hostname

share|improve this answer
    
"Invalid option" - the only flag available in man hostname for an IP address is i and that only returns the local loop... –  jasonwryan Aug 20 '13 at 21:44
    
You must be using a very very old version of hostname or have some kind of problem. In all new ubuntus that I have tried, and maybe olders too, it works perfectly well. –  Robert Vila Aug 20 '13 at 21:59
    
@mattdm: It is so clear that it needs no explanation It is clearer than all above explanations –  Robert Vila Aug 20 '13 at 22:01
1  
-I, --all-ip-addresses Display all network addresses of the host. This option enumerates all configured addresses on all network interfaces. The loopback interface and IPv6 link-local addresses are omitted. Contrary to option -i, this option does not depend on name resolution. Do not make any assumptions about the order of the output. That is why it works. –  Robert Vila Aug 20 '13 at 22:09
1  
Ubuntu is one flavour of Linux: you should never assume it is the default... –  jasonwryan Aug 22 '13 at 22:15

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.