Ok, try this then

#!/usr/bin/perl
use warnings;
use strict;

open my $a, "<", "file1.txt" or die "Failed to open File : $!";
open my $b, "<", "file2.txt" or die "Failed to open File : $!";

chomp(my @file1=<$a>);
chomp(my @file2=<$b>);

close $a;
close $b;

my $max = @file1;
my $min = 0;

while ($min < $max) {
    print "$file1[$min] : $file2[$min]\n";
    $min++;
}
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That should print to standard out