use strict;
use warnings;

my %col_idx;

open(my $result_fh, '<', 'file')               # 3-arg safer
   or die("Unable to open input file: $!\n");  # $! meaningful

while (<$result_fh>) {
   chomp();                                    # chomp safer
   my @fields = split(/;/, $_);

   if ($. == 1) {
      @col_idx{@fields} = 0..$#fields;
   } else {
      # Do what you want here.
      print "$fields[$col_idx{name}], ";
      print "$fields[$col_idx{postcode}]\n";
   }
}