Hello Mjpaddy,

Really nicely pointed out by Anonymous Monk (DIFF), under the assumption that you are running a Linux OS. I you are not running Linux an alternative would be to install Cygwin and execute the commands through there, or simply with the command FC file_1 file_2. More information can be found here fc.

Also a Perl solution by Athanasius the (Text::Diff).

But I could resist posting another alternative solution, that I found extremely useful not only comparing files but also for general purposes.

The Array::Utils module where you compare arrays. It provides you with the ability to compare elements of each array.

Sample of file_1.txt based on your description.

This is line 1.
Another line number 2.
This is also another line 3.
[download]

Sample of file_2.txt based on your description.

This is line 1.
Another line number 5.
This is also another line 3.
[download]

Finally the code with the output based only two options. Read the module it can provide you with alternative output, I choose these two for demonstration purposes.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use Array::Utils qw(:all);

my $file_1 = "sample-1.txt";
my $file_2 = "sample-2.txt";
my $file_3 = "error.txt";

open (my $in_1, "<" , $file_1)
    or die "Could not open: ".$file_1." - $!\n";

open (my $in_2, "<" , $file_2)
    or die "Could not open: ".$file_2." - $!\n";

open (my $out, ">>" , $file_3)
    or die "Could not open: ".$file_3." - $!\n";

my @data_1 = <$in_1>;

chomp(@data_1);

my @data_2 = <$in_2>;

chomp(@data_2);

# symmetric difference
my @diff = array_diff(@data_1, @data_2);

print Dumper(\@diff);

# get items from array @data_1 that are not in array @data_2
my @minus = array_minus( @data_1 , @data_2 );

print Dumper(\@minus);

foreach $_ (@diff) {
    print $out $_ . "\n";
}

foreach $_ (@minus) {
    print $out $_ . "\n";
}

#print $out @diff;
#print $out @minus;

close ($in_1)
    or die ("Could not close: ".$file_1." - $!\n");

close ($in_2)
    or die ("Could not close: ".$file_2." - $!\n");

close ($out)
    or die ("Could not close: ".$file_3." - $!\n");

__END__

$VAR1 = [
          'Another line number 2.',
          'Another line number 5.'
        ];
$VAR1 = [
          'Another line number 2.'
        ];
[download]

Hope this helps.