#!/usr/bin/perl
use strict;
use warnings;

my @files = qw(bla1.txt bla2.txt bla3.txt bla4.txt);
my $output = 'blagesamt.txt';
open(my $write_fh, '>', $output) or die $!;
for my $file(@files){
   open(my $fh,'<',$file) or die $!;
   while(my $line = <$fh>){
    my $no_break_space = chr(0xa0);
       $write_fh $line.= $no_break_space/_/g;
        print $write_fh $line;
        $write_fh $line =~ s/$no_break_space/_/g;
            print $write_fh $line
        }
   close $fh;
   }
close $write_fh or die $!;