my $dir = "/dir1/dir2/dir3/$b";
opendir my $dh, 
    or die "Couldn't read directory '$dir'";
my @user_dir = map { "$dir/$_" } 
               grep { $_ !~ /^\.\.?$/ } readdir $dh;
...
foreach my $fileline (@user_dir) {
    my $filename = $fileline;
    ...
}