[Chicago-talk] Any handy operators for finding the local IP?

Steve Peters steve at fisharerojo.org
Tue Mar 15 11:45:38 PST 2005

On Tue, Mar 15, 2005 at 08:16:23AM -0800, Richard Reina wrote:
> I know there's a handy $< to find the UID of the user
> executing the prorgram.  Is there any handy operator
> to find the IP address of the local machine that is
> running the program.

The ways to get an IP address from Perl are less than 100% reliable.  To 
get something reliable, you have to get to a fairly low level on the
device.  With the help of Libnet (the C library), Inline::C, and root
access, its a piece of cake.


Steve Peters
steve at fisharerojo.org

#!/usr/bin/perl -w

use Inline ( C => 'DATA',
                 LIBS => '-L/usr/local/lib -lnet',
                 INC => '-I/usr/local/include',
                 AUTO_INCLUDE => '#include "libnet.h"'

print get_ip_address("fxp0"), "\n";


char* get_ip_address(char* device) {
    char* errbuf[LIBNET_ERRBUF_SIZE];
    libnet_t* l;
    u_int32_t ip;
    char* addr;

    l = libnet_init(LIBNET_LINK, device, errbuf);
    if (!l) {
         addr = libnet_geterror(l);
         return addr;

    ip = libnet_get_ipaddr4(l);

    if(-1 == ip) {
        addr = libnet_geterror(l);
    } else {
        addr = libnet_addr2name4(ip, LIBNET_DONT_RESOLVE);
    return addr;

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