my $line =~ tr/\xa0//d;

my $line =~ tr/\xa0//d;

'"my" variable $line masks earlier declaration in same scope' 

Use of uninitialized value in transliteration (tr///) at so_wie_es_sesin_soll5.pl line 10.

Global symbol "$line" requires explicit package name at so_wie_es_sesin_soll5.pl line 10.
Execution of so_wie_es_sesin_soll5.pl aborted due to compilation errors

 #!/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>){
    $line =~ tr/\xa0//d;
    print $write_fh $line;

   }
   close $fh;
}
close $write_fh or die $!;

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

my @files = qw(ZIEL1.txt ZIEL2.txt ZIEL3.txt ZIEL4.txt);
my $output = 'ZIELgesamt.txt';

open(my $write_fh, '>', $output) or die $!;
for my $file(@files){
    open(my $fh,'<',$file) or die $!;
    while(my $line = <$fh>){
        $line =~ tr/\xa0//d;
        print $write_fh $line;
    }
    close $fh;
}
close $write_fh or die $!;