open OUT, '>out.txt';

my @files = filesindir('.');

for my $file (@files) {
    next unless (($file =~ /\.txt$/) && ($file ne 'out.txt'));
    open FILE, '<'.$file;
    while (my $line = <FILE>) {
        print OUT $line;
    }
    close FILE;
    print OUT "\n";
}

close OUT;

sub filesindir {
    my $dir = shift;
    my $limit = shift;
    opendir(DIR, $dir);
    my @dots = grep { $_ !~ /^\./ && -f "$dir/$_" } readdir(DIR);
    closedir DIR;
    if ($limit) {
        @dots = shuffle(@dots);
        @dots = @dots[1..$limit];
    }
    return wantarray?@dots:\@dots;
}