Re^2: grep flip flop (range operator)

BONUS STUMPER: For all of the ones that don't print, they do print if you replace 1 with 0; however, all elements are printed instead of stopping at Q (shown below). For the one that did print, the change to 0 causes it to not print. Anyone able to explain this?

a
b
c
Q
r
s
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Re^3: grep flip flop (range operator) by davido (Cardinal) on Sep 13, 2012 at 07:23 UTC
`perl -E 'say "Yes!" if $. == 0;'` $. uninitialized if there's no file open for reading (undef). undef is false. In a numeric comparison, undef is promoted to zero (or conceptually better, zero is demoted to false, and undef is promoted to false). Consequently, `0 ..` is true, and the flip flop flips. If warnings were enabled you'd get one. :) Dave	[reply] [d/l] [select]
Re^4: grep flip flop (range operator) by frozenwithjoy (Priest) on Sep 13, 2012 at 07:26 UTC
Ah, yes.... and the reason it doesn't stop at `Q` is because it gets flipped right back on after `Q`. Apparently, my brain only works once per night. Thanks!	[reply] [d/l] [select]
Re^3: grep flip flop (range operator) by grizzley (Chaplain) on Sep 13, 2012 at 08:51 UTC
Whole list is printed, as after spotting 'Q' flip-flop goes to 'false' state and back to condition `$. == 0` which is all the time true, so it sets flip-flop again to true.	[reply] [d/l]