Hello Anonymous Monk,

I would approach your problem a bit more different. I would use File::Find::Rule to find all the files you want to compare. Why? Simply because you can use regex plus it can search on multiple directories recursively, what more can you ask.

Second step I would use List::Compare/Regular Case: Compare Two Lists, why? Simply because for me since I have the list with files that I want to compare I simply need to open one by one the file and compare with the array of data that you are trying to compare on your example for(@sd){ push @out, $_ if (not @out) or ($out[-1] ne $_); };. The module does not need to sort the data it will compare each line individually.

Example with solution provided bellow:

#!usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use List::Compare;
use File::Find::Rule;

sub get_files {
    my @dirs = ('/home/tinyos/Monks/uniq');
    my $level = shift // 2;

    my @files = File::Find::Rule->file()
    ->name('*.txt')
    ->maxdepth($level)
    ->in(@dirs);

    return @files;
}

my @files = get_files();

# print Dumper \@files if @files;

# file to compare against the rest
my $path2compare = '/home/tinyos/Monks/uniq/compare.txt';
open my $fh, '<', $path2compare
    or die "Can't open file $path2compare: $!";
chomp(my @array2compare = <$fh>);
close $fh
    or warn "File $path2compare close failed: $!";

# open files and load them into an array
# compare unique lines and store them into a Hash of Arrays
my %HoA;
foreach my $path_to_file (@files) {
    open my $fh, '<', $path_to_file
    or die "Can't open file $path_to_file: $!";
    chomp(my @lines = <$fh>);
    close $fh
    or warn "File $path_to_file close failed: $!";
    my $lc = List::Compare->new('-u', \@array2compare, \@lines);
    # Get those items which appear at least once in both lists (their 
+intersection).
    my @intersection = $lc->get_intersection;
    # Get those items which appear (at least once) only in the second 
+list.
    # my @Ronly = $lc->get_complement;
    # print Dumper \@Ronly;
    # write to file here
    $HoA{$path_to_file} = \@intersection;
}

print Dumper \%HoA;

__END__

$ perl unique.pl
$VAR1 = {
          '/home/tinyos/Monks/uniq/compare.txt' => [
                                                     'Common line',
                                                     'Unique line file
+ Original'
                                                   ],
          '/home/tinyos/Monks/uniq/unique1.txt' => [
                                                     'Common line'
                                                   ],
          '/home/tinyos/Monks/uniq/unique2.txt' => [
                                                     'Common line'
                                                   ]
        };

uniqu1.txt
Unique line file1
Common line

uniqu2.txt
Common line
Unique line file2

compare.txt
Unique line file Original
Common line
[download]

Based on you code, I noticed a few things. Always always!!!!!!! use strict; use warnings;. Also do not use bare words for file handles, read here why Don't Open Files in the old way. Every time you open a file handle or close one use die or warn.

Update: adding one more method in script, plus a bit of explanation.

Update2: adding opening original file to compare against, also update output.

Hope this helps, BR.