[...]
# read files
my $data_to_append = &datei_lesen($erste_datei,0);
my $full_data = &datei_lesen($andere_datei,1);[...]

sub datei_lesen{
   # pick parameters
   my($file,$index) = @_;

   # open file
   open(my$fhIN, '<', $file)
       or die "open failed: $!";

   # read data
   my %data;
   while (my$line=<$fhIN>)
   {
       chomp($line);

       # split line
       my @tracts = split('#', $line);

       # key equals the first tract
       my $key = $tracts[$index];
       my $val = [@tracts];

       # push data
       $data{$key} = [] unless exists $data{$key};
        push(@{$data{$key}}, $val);
   }

   # close file
   close($fhIN);

   # return data reference
   return \%data;
} # datei_lesen