for($/)x16
[download]

A slick way of getting the newline (vis-à-vis -l print until...)! Changing the loop to for($_)x16 is informative. And, since a bare print prints both $_ and $/, I found it rather unobvious which variable holds the strings.

Actually, $/ is the input record separator, so a bare print does not print it. What's being printed is just the (localized) $_ inside the for loop. Of course, a bare print will print $\, aka the output record separator, often seen in golf, as in, for example, The golf course looks great, my swing feels good, I like my chances (Part I).

The for($/)x16 loop aliases $/ and, despite the x16, only the single $/ value is (repeatedly) changed, as you will discover by printing it after the loop has terminated. Replacing "print" with "warn" like so:

s/^|\d+/$&+$'||1/eg,warn("du='$_' ds='$/'\n"),s// /for($/)x16;
warn("at end du='$_' ds='$/'\n");
[download]

should clarify. BTW, this eccentric "for loop aliasing" trick is often seen in golf; see, for example, Drunk on golf: 99 Bottles of Beer in the "Bottle Golf Tip No 2" section (search for Cantor). Finally, the "for loop aliasing" trick is a specific example of Eugene van der Pijll's general golfing mantra, "Can't possibly work, let's try it anyway". :)

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