next if ( $c++ == 0 ); # skip the file header

##</code><code>##

#!/usr/bin/perl -w
use strict;

my @master_list = ();

readfile("f1.lst", \@master_list);
readfile("f2.lst", \@master_list);
readfile("f3.lst", \@master_list);

printf "%s | %s | %s\n", @{$_}[0..2] for(@master_list);

sub readfile {
  my $filename = shift or die "Need filename.\n";
  my $listref = shift; # Listed pointed to is modified in place.

  open my $file, "< $filename" or die "Can't open $filename: $!\n";

  my $header = <$file>;

  my $c = 0;
  local $_;
  while(<$file>) {
    $listref->[$c] ||= []; # use strict doesn't like auto-viv.
    chomp;
    # Compare the new value with the first value stored in the list.
    # First value to be read in for any row is assumed to be
    # correct.  All subsequent values must match that first one.
    unless(@{$listref->[$c]} and $_ != $listref->[$c][0]) {
      push @{$listref->[$c]}, $_;
    } else {
      push @{$listref->[$c]}, ' ';
    }

    ++$c;
  }

  close $file or die "Can't close $filename: $!\n";
}