$ paste xdaten.dat ydaten.dat > xydaten.dat
$ echo "plot 'xydaten.dat' w lp" | gnuplot -persist

#! /usr/bin/perl

use strict;
use warnings;

my $n_file = 'path/to/file_with_number.txt';
my $d_file = 'path/to/file_with_diameters.txt';
my $out  = '/path/to/outfile.dat'

my @numbers = ();
my @diameters = ();

# anzahl einlesen;
open(R_N,"<$n_file") or die $!;
my @lines_n = <R_N>;
close R_N;
chomp(@lines_n);
foreach(@lines_n){
  push(@numbers,split(/ /,$_));
}

# durchmesser einlesen
open(R_D,"<$d_file") or die $!;
my @lines_d = <R_D>;
close R_D;
chomp(@lines_d);
foreach(@lines_d){
  push(@diameters,split(/ /,$_));
}

open(W_FILE,">$out") or die $!;
for(0..$#numbers){
  print $numbers[$_]," ",$diameters[$_];
}
close W_FILE;

#! /usr/bin/perl

use strict;
use warnings;

my $n_file = 'path/to/file_with_number.txt';
my $out  = '/path/to/outfile.dat'

my @numbers = ();
my @diameters = ();

# anzahl einlesen;
open(R_N,"<$n_file") or die $!;
my @lines_n = <R_N>;
close R_N;
chomp(@lines_n);
for(my $i = 0; $i < $#lines_n; $i += 2){
  push(@numbers,split(/ /,$lines_n[$i]));
  push(@diameters,split(/ /,$lines_n[$i+1]));
}

open(W_FILE,">$out") or die $!;
for(0..$#numbers){
 print $numbers[$_]," ",$diameters[$_];
}
close W_FILE;

for(0..$#numbers){
  print W_FILE $numbers[$_]," ",$diameters[$_],"\n";
}