my $dir = 'test2';
opendir(DIR,$dir) or die $!;
while($datei = readdir(DIR)){ 
    my $path = $dir . '/' . $datei;
    next unless -f $path;
    my @entries;
    {
        my $measure;
        local $/ = "\nDUT No\n";
        open my $fh, '<', $path or die $!;
        while( my $entry = <$fh> ){
            chomp $entry;
            @mms = $entry =~ /Measurement:\s*([\d.]+)/;
            $measure = $mms[0] unless defined $measure;
            if(grep{ $_ == $measure }@mms){
                $entry = "DUT No\n". $entry unless $entry =~ /^DUT No/;
                push @entries, $entry;
            }
        }
    }

    print $_,"\n" for @entries;
    close OUTPUT;

}