my $order_daten = $ENV{ORDNER_DATEN}; # Pfad zu den Daten

my @stations_namen = ("1231","1232","1233","1234","1235");

foreach my $name (@stations_namen) {
  ########  EINLESEN 

  my @stationsdaten;

  my $filename = "$order_daten$name/${name}_$datum_heute.txt";
  push(@stationsdaten,read_file($filename));

  my $filename2 = "$order_daten$name/${name}_$datum_gestern.txt";
  push(@stationsdaten,read_file($filename2));

  print Dumper \@stationsdaten;
}

# ...

sub read_file{
  my $filename=shift;

  open(my $eingang, '<', $filename) or die "can't open $filename: $!\n" ;
  my @lines=<$eingang>;
  close($eingang);

  return @lines;
}