Then you'll have to go through the records, using grep if you want to filter the whole list at once, or using if if going through them one at a time.

Assuming you have a hash per record:

• One at a time:

  my @section;
  while(my $r = $db->fetchrow) {
      push @section, $r if $r->{name} =~ /^A/i;
  }
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• All at once:

  my @section = grep { $_->{name} =~ /^A/i } $db->fetchrows;
  [download]

This is pseudocode, you must fill in the details on how to get the data from the flatfile, yourself.