# ... file is opened in handle FH

my ($compname, $hdrdata, $tlrdata );
while (<FH>) {
  /^HDR(\w+)\s+(\w+)/ && do {
    $compname=$1;
    $hdrdata=$2;
    # handle a header
    next;
  };
  /^TLR(\d+)/ && do {
    $tlrdata=$1;
    # handle a trailer with number=$1
    next;
  };
  /^ADD(?:RANGE)?|DELETE(?:RANGE)?/ && do {
    my ($type,@range_data) = split /,/;
    my $comp_rec = pop @range_data;
    if ($comp_name eq $comp_rec ) {  # validate record
      # process type, range data, etc.
    }
    else {
      # error?
    }
    next;
  };

  # any other kind of line falls through here
  # error: ...
}