1 #!/usr/bin/perl -w
      2 use strict;
      3
      4 my @master_list = ();
      5
      6 readfile("f1.lst", \@master_list);
      7 readfile("f2.lst", \@master_list);
      8 readfile("f3.lst", \@master_list);
      9
     10 printf "%s | %s | %s\n", @{$_}[0..2] for(@master_list);
     11
     12 sub readfile {
     13   my $filename = shift or die "Need filename.\n";
     14   my $listref = shift; # Listed pointed to is modified in place.
     15
     16   open my $file, "< $filename" or die "Can't open $filename: $!\n";
     17
     18   my $header = <$file>;
     19
     20   my $c = 0;
     21   local $_;
     22   while(<$file>) {
     23     $listref->[$c] ||= []; # use strict doesn't like auto-viv.
     24     chomp;
     25     # Compare the new value with the first value stored in the list.
     26     # First value to be read in for any row is assumed to be
     27     # correct.  All subsequent values must match that first one.
     28     unless(@{$listref->[$c]} and $_ != $listref->[$c][0]) {
     29       push @{$listref->[$c]}, $_;
     30     } else {
     31       push @{$listref->[$c]}, ' ';
     32     }
     33
     34     ++$c;
     35   }
     36
     37   close $file or die "Can't close $filename: $!\n";
     38 }

##</code><code>##

    unless(@{$listref->[$c]} and $_ != $listref->[$c][0]) {
      push @{$listref->[$c]}, $_;
    } else {
      push @{$listref->[$c]}, ' ';
    }