What's my IP? 3

[skiflyer]

How do I figure out my IP address on a linux machine? (It was assigned via DHCP.

Thanks,

Rob

(And I'm behind a firewall, so a website which'll spit it back won't work)

 

[sleipnir214]

ifconfig should do it from a command line. Want the best answers? Ask the best questions:

http://www.catb.org/~esr/faqs/smart-questions.html

TANSTAAFL!

 

[ppc386]

This little script works for me -
[tt]
#!/bin/bash
/sbin/ifconfig | (grep 'inet addr:.*P\-t\-P' || echo '127.0.0.1') | awk '{sub(/inet addr:/, "" printf("%s\n", $1)}'
[/tt]

 

[clonny2]

'ifconfig' will give you all network connections.


'ifconfig eth0' will give you only eth0 (the first ethernet device) information.


Next examine the output

inet addr: is your IP address. Bcast: Broadcast and Mask: is your netmask

The above script from ppc386 is more complicated than you need.

This will work
ifconfig eth0 | grep inet | awk '{print $2}'

Exchange eth0 for each device you want or just leave off eth0 to see all devices.

If you want to just see the ip and not see addr:x.x.x.x then add | awk -F ":" '{print $2}' to the command earlier. This will split addr:x.x.x.x into 2 seperate fields split on the :. $1 everything before the : and $2 everything after the colon.

 

[ppc386]

> The above script from ppc386 is more complicated than you need.

I guess that depends on what you need.

The reason I put "#!/bin/bash" at the beginning of my scripts
is so the "file" command will tell me it is a script.
So if I do:
% file ~/bin/my-ip
I get:
~/bin/my-ip: Bourne-Again shell script text
instead of:
~/bin/my-ip: ASCII English text

That way, I can do something like:
file ~/bin/* | grep Bourne
- to get a list of all the scripts in a directory.

Since /sbin/ is only in the path for root on my machine,
I have to specify /sbin/ifconfig to run the script as
a normal user.

I connect to the net with a dial-up connection, so if the
connection is down, doing "ifconfig ppp0" gives me nothing
but an ugly error message:

ppp0: error fetching interface information: Device not found

That's not what I want, I would rather get the loopback IP if
ppp0 is down ( that's what the "|| echo 127.0.0.1" is about )

As far as chopping the "inet addr:" from the string...

I really don't see how my:
awk '{sub(/inet addr:/, "" printf("%s\n", $1)}'

is any more complicated than your:
awk '{print $2}' | awk -F ":" '{print $2}'

Why use two awks when one will do?

I like your idea of specifying the interface though,
( it cleans up the grep expression )

So I changed my script a little -
[tt]
/sbin/ifconfig ppp0 2> /dev/null | (grep inet || echo 127.0.0.1) | awk '{sub(/inet addr:/, "" printf("%s\n", $1)}'
[/tt]

 

[clonny2]

ppc386

you are correct. It really does depend on your needs. And true why use 2 awks if you can use just 1. Kinda habit really for me from my earlier days.

I like your awk better, I should take time to learn more advanced awk techniques. Thanx for the tip as well.

 

[ppc386]

That's the beautiful thing about open source, we all learn
from each other. To be honest, I didn't even know you could
specify an interface to ifconfig. So I learned something here
as well.

I tried reading through the awk maual, and picked up a couple
of tricks just before smoke started coming out my ears. [tt]*-@v@-*[/tt]

So I still have a long way to go...

tnx 2u2

- Jeff

 

[danielhozac]

Well, why use [tt]grep[/tt] and [tt]awk[/tt] when you can just use [tt]awk[/tt]?

[tt]#!/bin/bash

/sbin/ifconfig | awk '{
if ($0 ~ "inet addr&quot
{
sub("addr:", "", $2)
print $2
}
}'[/tt] //Daniel

 

[ppc386]

Cool !

One more slight change:

[tt]
#!/bin/bash

/sbin/ifconfig ppp0 2> /dev/null | awk '{
if ($0 ~ "inet addr&quot {
sub("addr:", "", $2)
print $2
found = 1
}
} END { if ( !found ) { print "127.0.0.1" }
}'

[/tt]