for my $funcname (qw/basename dirname/)
{
    no strict 'refs';

    *$funcname = sub
    {
        my ($dir) = shift;

        my ($path, $name) = ($dir =~ m{(.*)/([^/]*)$});

        if ($funcname eq 'basename')
        {
            return $name;
        }
        else
        {
            return $path;
        }
    };
}

my $path = dirname('/tmp/foo/bar');
my $name = basename('/tmp/foo/bar');
print "$path/$name\n";