Re: Getting my WAN IP address from ppp0

[Stephan Hochhaus]

Hi Zach,

Well, this almost works for me.

#!perl
my $ifconfig = `ifconfig`; # the ifconfig command gives the current 
network information
$ifconfig =~ /inet (\d+\.\d+\.\d+\.\d+)/; # extract the ip address 
with a regular expression
This does extract my IP address, but the one for the loopback device 
lo0. The ifconfig output looks like this:

lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet6 ::1 prefixlen 128
        inet6 fe80::1 prefixlen 64 scopeid 0x1
        inet 127.0.0.1 netmask 0xff000000
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        tunnel inet  -->
        ether 00:30:65:ef:a8:f0
        media: autoselect (10baseT/UTP <half-duplex>) status: active
        supported media: none autoselect 10baseT/UTP <half-duplex> 
10baseT/UTP <full-duplex> 10baseT/UTP <full-duplex,hw-loopback> 
100baseTX <half-duplex> 100baseTX <full-duplex> 100baseTX 
<full-duplex,hw-loopback> 1000baseTX <full-duplex> 1000baseTX 
<full-duplex,hw-loopback> 1000baseTX <full-duplex,flow-control> 
1000baseTX <full-duplex,flow-control,hw-loopback>
fw0: flags=8822<BROADCAST,SMART,SIMPLEX,MULTICAST> mtu 2030
        tunnel inet  -->
        lladdr 00:30:65:ff:fe:ef:a8:f0
        media: autoselect <full-duplex> status: inactive
        supported media: autoselect <full-duplex>
ppp0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1492
        inet 212.212.2.212 --> 212.128.128.12 netmask 0xffffff00

Now I would like to start reading the output from just the last line. 
Is there anyway to start reading it from the end to the beginning and 
stop once the inet line is found?

my $ip = $1;
what's $1? Why is that needed?
I suppose it is an internal perl variable like $_, right?
The reason I don't want to use dyndns is, that I don't completely trust 
it and I might sometimes not need it for more than 30 days which leads 
to expiration of the address if I read things correctly.

Thanks a lot for your help.

Stephan