A slick way of getting the newline (vis-ā-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.
is the input
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");
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
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"