I always look at these golf challenges and think "I bet x would be shorter" but it rarely is. Anyway:

sub ruler {
    my($n,$r) = (int($_[0]+9)/10, ' ');
    $r .= sprintf"%10s",$_ for (1..$n);
    "$r\n" . '0123456789' x $n . "0\n";
}
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The sprintf would save a few strokes in your code but nothing significant. I'll take your word for it that there is a column 0. ;-)

For shorter rulers I often use a sequence like this which fits on one line and is easy to count::

123456789_123456789_123456789_123456789_123456789_123456789_
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John.
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