#!/usr/bin/perl

# http://perlmonks.org/?node_id=1140982

use Algorithm::Diff qw(traverse_sequences);
use strict;
use warnings;

my $file1 = <<END;
system
     security
         management-ip
             protocol
                    internal
                    shutdown
                    allow
                    entry 1
                        snmp ok
                    exit 
END

my $file2 = <<END;
system
     security
         management-ip
             protocol
                    internal
                    shutdown
                    allow
                    entry 1
                        snmp failed
                    exit 
END

sub fullpath
  {
  my @full;
  my @answer;
  for my $line ( shift() =~ /.+\n/g )
    {
    $line =~ /^( *)/;
    $#full = length($1) - 1; # truncate array
    push @full, $line;
    push @answer, join '', grep defined, @full;
    }
  return \@answer;
  }

my $full1 = fullpath($file1);
my $full2 = fullpath($file2);

traverse_sequences( $full1, $full2,
  {
  DISCARD_A => sub {print $full1->[shift()], "\n"},
  } );