It's good that you have a working version now. There are some things you could improve, though:

• use strict;!!
• more flexibility through non-hard coded filenames
• error checking on opening files
• localising $_
• eliminate select statements

So an improved version of your sub would look like this:

sub indextime {
  my ($infile, $outfile) = @_;
  open my $in, '<', $infile or die "Couldn't open $infile for reading:
+ $!";
  open my $out, '>', $outfile or die "Couldn't open $outfile for writi
+ng: $!";

  my @matrix;
  local $_;
  push @matrix, [split] while <$in>;

  my ($storenum, $date) = @{$matrix[0]}[0,1];
  print $out "@{$matrix[$_]} $storenum $date\n"
    for 6..$#matrix-1;

  close $in  or die $!;
  close $out or die $!;
}
[download]

-- Hofmator