This is what I currently recommend:

ip route get 8.8.8.8 | awk '{print $NF; exit}'

The advantage of that command is that you don't have to know which interface you are using (eth0? eth1? or maybe wlan0?), you don't have to filter out localhost addresses, or Docker addresses, or VPN tunnels etc. and you will always get the IP address that is currently used for Internet connections at that very moment (important when e.g. you are connected with both ethernet and wifi or via VPN etc.).

This will test not only that you have a correct IP configured on some interface (like with parsing the output of ifconfig) but also that you have the routing table configured to use it correctly.

I found that idea in this answer
by Collin Anderson.

I use it in the internalip script in my scripts collection on GitHub, which you can install with:

wget https://rawgit.com/rsp/scripts/master/internalip

chmod a+x internalip

and use as:

internalip

or:

internalip TARGET

and you will get your IP address that would be used to connect with the TARGET IP address. The default target is 8.8.8.8 which is the Google's public DNS resolver and a good default for the Internet.

But if you run it with a different IP:

internalip 127.2.3.4

Then you will get:

127.0.0.1

because that is your IP address that would be used to connect with 127.2.3.4 on the loopback interface. It's useful when your target is on a LAN, VPN or other special network, in which case some other IP could be used for connections than the default IP for reaching the Internet.

External IP

To check your external IP address (the one that the servers on the Internet see when you connect to them - which may be different than the internal IP address described here) see this answer.

hostname -I

This will give you just ip address without any extra information.

I think it worth mentioning that running ifconfig along with -a option will display all interfaces wether or not the interface has an IP.

running ifconfig alone, will display only interfaces with IPs assigned.

Here is a nice trick you could use to display only IPs using Perl.

# ifconfig | perl -nle'/dr:(S+)/ && print $1'

192.168.1.100

127.0.0.1

Your network card is recognized by the system, that why its showing up eth0 and eth1

here is a quick way of assigning IP to your interface, use valid IP/Subnet accordingly.

 ifconfig eth0 192.168.1.200/24 up 

then we need to add a default route

route add default gw 192.168.1.1

Best,

This command will show all the IP addresses for a single device:

dev=eth0

ip addr show $dev | awk '/inet/ {print $2}' | cut -d/ -f1

It will print one or two lines of output. The first one is the inet/IPv4 address and the other one is inet6/IPv6 if your system is configured to support this.

In case, the ifconfig command didn't display the IP address, there is a very simple and easy way to find out the IP address of the Ubuntu machine through the GUI. Follow the steps below:

Click the network icon in the notification area and click Connection Information.

This brings up a window which has a some information, including the IP address.

There's lots of good answers here to choose from already, but I thought I'd point out facter which is usually, but not necessarily used with puppet for collecting various facts about the system. The main advantage of facter is that it gives nice clean output which saves you all the manipulation with grep, sed, awk, cut, perl, etc. It isn't going to tell you which interface you're interested in, but if you know that, then the following gives you the IP without other cruft to clean up:

facter ipaddress_eth0 

ip command

Here's a variation on ip addr way.

ip has -o option which allows putting all information on single line - this is useful for parsing with tools like awk or perl. In combination with -4 option, we will only see IPv4 addresses. Thus, output would be something like this (note - replace wlan7 with the interface you want to check):

$ ip -4 -o addr show wlan7

3: wlan7    inet 192.168.0.78/24 brd 192.168.0.255 scope global dynamic wlan7       valid_lft 85654sec preferred_lft 85654sec

As you can see, the IP address is 4th column/word in the output. The rest , is simple parsing exercise via the tool of your choice. Here, I'm using python:

ip -4 -o addr show wlan7 | python -c "import sys;print sys.stdin.readlines()[0].split()[3]" 

Same thing, only with here string <<< and command substitution $()

python -c "import sys;print sys.stdin.readlines()[0].split()[3]"  <<< $(ip -4 -o addr show wlan7)

Personally, I have this saved as a nice function in my ~/.bashrc so less typing is done.

wlan_ip() {

    ip -4 -o addr show wlan7 | python -c "import sys;print sys.stdin.readlines()[0].split()[3]" 

} 

Perl's and Ruby's version are a bit shorter:

$ ip -4 -o addr show  wlan7 | perl -lane 'print $F[3]'                         

192.168.0.78/24



$ ip  -4 -o addr show wlan7 | ruby -n -e 'print $_.split()[3]'                 

192.168.0.78/24

Wireshark

If you're familiar with using network analysis tools, you probably know that to get your ip address, all you need to do is clear the browser cache, start Wireshark capture on the specific interface, and look for http GET packets being transmitted. The destination column will show your ip address