file1::line1
file2::line1
file3::line1
file1::line2
file2::line2
file3::line2
...

##</code><code>##

file1::line12
file2::line12
file3::line12
file1::line1
file2::line1
file3::line1
file1::line1
file2::line1
file3::line1
...

##</code><code>##

#!/usr/bin/perl -w

# These files have this format:
# filename::line number (e.g., 1.txt::1)
 
my @files = (
		"1.txt",
		"2.txt",
		"3.txt",
             );

my $total_strings = 9;
my $cur_pos = 0;
my $next_pos = 0;

open(MIXED, ">mixed.txt") || die "(x) Failed: mixed.txt - $!\n";

  for (my $cur_string=1; $cur_string <= $total_strings; $cur_string++) {

  print "\nCurrent String: $cur_string of $total_strings\n";

    foreach my $file (@files) {

        print " Opening File: $file\n";
        print " Current Position is: $cur_pos\n";

        open(FILE, $file) || die "(x) Failed: $file - $!\n";
         while(<FILE>) {
           seek(FILE, $cur_pos, 1);
           $string = $_;
           $next_pos = tell(FILE);
         }
        close(FILE);

           print " Read string: $string";
           print MIXED $string;
           print " Next Position is: $next_pos\n\n";

      }
    $cur_pos = $next_pos;
  }

close(MIXED);