my $stn; # current stn hash being constructed
...
while (<IN>) {
  if (/^H/ || /^reclin/i) {
    if ($stn) {
      ...save $stn...;
      $stn = undef; # reset stn hash
    }
  }

  if (/^H/ ... /[<\[]/) { ... same code ... }
  next if (/^reclin/i);

  ... parse new $stn hash values ...
  $stn->{$s} = [ $x, $y, $z ];
}
if ($stn) {
  ...save $stn...
}