Environment variable for ip address

Question

I see somewhere people use:

IF_ADDRESS="$(echo "$IP4_ADDRESS_0" | cut -d'/' -f1)"

to get the IP address in a network configuration script. In my system, I create a script under the directory /etc/network/if-up.d/ and test with:

echo "$IP4_ADDRESS_0" >> /tmp/test.log

but get nothing with this variable. What's wrong?

My /etc/network/interfaces is like this:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

My final purpose is to set up the IP routing policy with a script like this.

Solution

$IP4_ADDRESS_0 is a variable, so it's likely not set. You can see it's value with this command:

$ echo "$IP4_ADDRESS_0"

If it's blank you'll see this:

$ echo "$IP4_ADDRESS_0"

$

You could use this command instead:

$ ifconfig eth0 | grep 'inet addr:' | cut -d: -f2 | awk '{ print $1}'
192.168.1.27

Comments

[platinor]

Yes, it works. So $IP4_ADDRESS_0 is not a predefined variable like the $IFACE or $METHOD, right?

[slm]

@platinor - I don't think so. If you use the command grep IP4 /etc/network/if-up.d/* you don't find any examples of it being used there.

[Kusalananda]

The variable probably comes from some kind of dispatcher script relating to something called "NetworkManager" on Linux. I'm not a Linux guy, but that's what came up when searching.