Read UNIX / Linux System IP Address In a Shell Script

Posted on in Categories Linux, Shell scripting last updated May 28, 2011

Reading an IP address in shell script required many time. However, different Linux distribution stores IP address in different files. If you are looking to run script under different UNIX like OSes such as Solaris or FreeBSD then you need to use the ifconfig command. The ifconfig command is not just used to configure a network interface, but it can be use to obtained information such as network IP, netmask and much more.

Linux ifconfig Example

Type the following command:

ifconfig  | grep 'inet addr:'| grep -v '127.0.0.1' | cut -d: -f2 | awk '{ print $1}'

FreeBSD/OpenBSD ifconfig Example

Type the following command:

ifconfig  | grep -E 'inet.[0-9]' | grep -v '127.0.0.1' | awk '{ print $2}'

Sun / Oracle Solaris Unix Example:

Type the following command:

ifconfig -a | grep inet | grep -v '127.0.0.1' | awk '{ print $2}'

Note: use /sbin/ifconfig full path if you are the non-root user.

How Does It Works?

You are using the ifconfig command and sending its output to shell pipeline. A pipeline is a set of processes chained by their standard streams, so that the output of each process (“stdout”) feeds directly as input (“stdin”) of the next one.

  1. The ifconfig command list all network interfaces.
  2. From the output of ifconfig command, find out IPv4 IP address using the grep command (grep ‘inet addr:’).
  3. Next, you do not need loopback IP address (127.0.0.1) so again with the help of grep –v you invert the sense of matching, to select all non-matching lines.
  4. Finally, awk command is used to select an IP address. (awk ‘{print $2}’)

See also: read-ip-address.bash script which reads/finds an IP address from different UNIX/Linux OSes.

32 comment

  1. The process you listed would only give you the local address, if you are behind a firewall that uses NAT.

    To get your public IP address try out the following bash script that I wrote a while ago:

    #!/bin/bash

    wget whatismyip.org
    read T1 http://www.suramya.com

  2. True, This script is actually a portion of another script that sends out an email when my public IP changes. I just copied the portion that actually gets the IP and pasted it here.

    That being said your version of the script is a lot cleaner. Mind if I ‘steal’ it for use in my scripts? ;)

    Thanks,
    Suramya

  3. Hi there,

    I’m new to all this and I was wondering, how do those websites get our IP and is there not a shell script that can be written to find out your public IP depending on your private IP without having to use these external websites?

  4. @Clue
    no. for as far as I know you’ll always need some external server to ‘see’ who you are.
    But if someone knows another way to do this, the n please let me know.

  5. if you use a different locale, consider this version for linux:

    LC_ALL=C ifconfig | grep ‘inet addr:’| grep -v ‘127.0.0.1’ | cut -d: -f2 | awk ‘{ print $1}’

  6. @the suggestion of using whatsmyip.

    That is a great idea, but if you’re looking to find your ip address on a box that has no internet access then that would not work and the original script(s) should always work. If you’re on a private lan for example with no web access then you can’t see whatsmyip, or ipchicken, etc.

    This quick how-to is not so much on how to find your external IP address, but more on the actual address your system has been assigned either DHCP, or statically.

  7. @mohan, you can have multiple separators and not have to rerun awk.
    @paul, do you like yours because it has a sed abomination in it? Make it simple!

    ifconfig eth0 | awk -F”[: ]+” ‘NR==2 {print $4}’

  8. OMFG, guys, please, you *do* realize anybody can hack into whatismyip.org and INSTANTLY gain access to your boxes ?!!!! And you’re not even using HTTPS – so any monkey in the middle can 0wn your boxes too !!!!
    Are you dumb enough to run those lynx/curl scripts as root as well ???

    NEVER EVER put this much trust into 3rd party systems, or you WILL get screwed !

    it would be funny watching you after whatismyip.org returns `rm -rf /`

    use ifconfig / ip show… and don’t be so freaking lazy

    1. Yeah, because lynx/curl execute the returned website. That’s how they work. Didn’t you know? They take what whatsmyip.org respond with, pass it into a system() call and it gets executed. Yup. And when you’re executing lynx as your user (which nobody suggested to do otherwise) rm -rf / is still able to wipe out your hard drive, because well… linux just doesn’t have a permissions system.

      ifconfig on the other hand, an administrator’s tool which sends a lot of information about your network interfaces to your shell, potentially sending the result in an email if the script is run from cron; well, that’s just brilliant. So much more secure. I’d definitely recommend using ifconfig. Yup. Blast a load of intimate hardware details across SMTP, way more secure than fetching a HTML response from a web server that contains nothing but your IP address.

      Seriously, though, if you’re gonna get angry at people for lax security practices at least have a clue what you’re talking about first.

      1. The result from curl is not interpreted by curl itself, but might be by the shell script if not carefully written. Shell script injection is a common attack vector. If it happens, it’s already a huge security breach, even if the script doesn’t run as root.

        “hostname -i” or even parsed ifconfig is much more secure, just don’t print the result if it contains sensitive data.

  9. This can be done exclusively in bash, if you’re interested in shaving a ms or two.
    IP=`ifconfig`
    IP=${IP#*inet addr:}
    IP=${IP%% *}

  10. You can also do it in cygwin (you have to use Microsoft’s ipconfig command):

    ipconfig | grep ‘IP Address’ | grep -v 0.0.0.0 | awk ‘{ print $15}’
    ($15 signifies the 15th word – the dots are words too!)

    Therefore, to mimic cygwin’s default prompt, use:

    export PS1=”\[\e]0;\w\a\]\n\[\e[32m\]\u@`ipconfig | grep ‘IP Address’ | grep -v 0.0.0.0 | awk ‘{ print $15}’` \[\e[33m\]\w\[\e[0m\]\n\$”

    This work for me, but it’s a bit system specific. For example, if you have additional network interfaces, you may have to grep -v any others that might be returned.

    Dan

  11. bsr,
    can any1 plzzzzz tell me wat’s the utility of this script (it gives the local address i know!! but y know my local address?!!!!!).
    Thks.

  12. hey i want to know: the code for running a shell script to connect a Setup Box(STB) through Jenkins integration tool by fetching its IP or MAC address. Please help..

  13. Update for Fedora v17 as the examples above won’t work.

    ifconfig | grep ‘inet’| grep -v ‘127.0.0.1’ | cut -d: -f2 | awk ‘{ print $2}’

  14. Keep only one grep.

    ifconfig wlan0 | grep -o -P ‘(?<=addr:)[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+\s'

    ——-
    Ubuntu 13.04

  15. Hi, in CentOS el7 ….. this command changed to :
    ifconfig | grep ‘inet ‘| grep -v ‘127.0.0.1’ | cut -d: -f2 | awk ‘{ print $2}’

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