Seems to do what you showed. If not, please say why and provide a more extensive test case. 

#!/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"},
  } );

[download]

In reply to Re: Finding the parent of a text in a file by Anonymous Monk
in thread Finding the parent of a text in a file by ExperimentsWithPerl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.