Here is one technique:

#usr/bin/perl -w
use strict;
use Data::Dump qw(pp);

my %hash;

while (my $line = <DATA>)
{
   my ($edit) = ($line =~ m/^\s*edit\s*\"(.*)\"/)[0];
   next unless $edit;  #find first "edit line"
   my $ip = get_ip();  #get ip if it exists in this record
                       #else $ip is a null (not found)
   $hash{$edit}=$ip if $ip;
}

#returns ip = null if a valid ip is not found in this record
#end of record is "next"

sub get_ip
{  
   while (<DATA>)
   {
      my ($ip) = ($_ =~ /^\s*set ip\s*([\d\.]+)/)[0];
      return $ip if ($ip or /next/);
   }
}   

print pp \%hash;

=prints
{
  dmz => "192.18.254.1",
  internal1 => "10.1.16.3",
  internal2 => "192.168.2.1",
  wan1 => "1.1.1.1",
  wan2 => "10.4.254.198",
}
=cut

__DATA__

config system interface
    edit "dmz"
        set vdom "root"
        set ip 192.18.254.1 255.255.254.0
        set allowaccess ping fgfm
        set type physical
        set alias "Guest-Wlan"
    next
    edit "wan2"
        set vdom "test"
        set ip 10.4.254.198 255.255.255.252
        set allowaccess ping https ssh snmp
        set type physical
        set alias "To MON ospf int"
    next
    edit "wan1"
        set vdom "root"
        set ip 1.1.1.1 255.255.255.252
        set allowaccess ping https
        set type physical
        set alias "To Internet"
    next
    edit "modem"
        set vdom "root"
        set mode pppoe
        set allowaccess fgfm
        set type physical
    next
    edit "ssl.root"
        set vdom "root"
        set type tunnel
    next
    edit "ssl.MyRealm"
        set vdom "MyRealm"
        set type tunnel
    next
    edit "internal1"
        set vdom "root"
        set ip 10.1.16.3 255.255.255.0
        set allowaccess ping https ssh snmp fgfm
        set type physical
        set alias "To MON Internal "
    next
  edit "internal2"
        set vdom "MyRealm"
        set dhcp-relay-service enable
        set dhcp-relay-ip "192.168.1.1"
        set ip 192.168.2.1 255.255.254.0
        set allowaccess ping https ssh snmp fgfm
        set type physical
        set alias "To MINE"
    next
    edit "VPN-Dial"
        set vdom "root"
        set type tunnel
        set interface "wan1"
    next
end
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