use strict;

sub split_file_line {
   my $file = shift;
   open(IN, "<".$file) || die "cannot open $file: $!";
   my @items = split /,/,chomp($_ = <IN>);
   close IN;
   return \@items;
}
   
my @data = ();
my @files = qw(header_data.dat);
my $nfiles = 3;
for (my $i = 1; $i <= $nfiles; $i++) {
   push @files,"daily_data${i}.dat";
}

foreach my $file (@files) {
  push @data, split_file_line($file);
}