You can use Net::Interface to get the IP address associated with "eth0", such as:

use Socket qw(AF_INET pack_sockaddr_in);
use Net::Interface;

my $intf = Net::Interface->new('eth0');
my $ipaddr = $intf->address(AF_INET);
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and then bind() the socket to the local address as:

bind(SOCKET, pack_sockaddr_in(0, $ipaddr)) || die "can't bind socket t
+o local address";
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and this should achieve what you're asking to be able to do.