You can transform the input lines into "full paths", i.e. include all the antecendents to each element. Then, you can just run standard diff (Algorithm::Diff) on the items: 
#!/usr/bin/perl
use warnings;
use strict;

use Algorithm::Diff qw{ diff };


open my $F1, '<', '1.in' or die $!;
my @lines1 = <$F1>;

open my $F2, '<', '2.in' or die $!;
my @lines2 = <$F2>;

chomp @lines1;
chomp @lines2;

# Transform the input lines.
my @path = q();
my @indent = q();
for my $line (@lines1, @lines2) {
    my ($this_indent, $key) = $line =~ /^( +)(.*)/;
    if ($this_indent eq $indent[-1]) {
        $path[-1] = $key

    } else {
        if ($this_indent le $indent[-1]) {
            pop @indent, pop @path while $indent[-1] ge $this_indent;
        }
        push @path, $key;
        push @indent, $this_indent;
    }
    $line = join '/', @path;
}

# Compare the lines.
my @diffs = diff(\@lines1, \@lines2);
for my $diff (@diffs) {
    for my $line (@$diff) {
        print "@$line\n";
    }
}

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

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

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