Hello, all--

I've got a question that I can't answer[1]. Given this code:

#!/usr/bin/perl -w
use strict;
use warnings;

while (<DATA>) {
   if ($. % 10 == 1) {
      print;
      for my $cnt (0 .. 3) {
         <DATA>;  # my $t=<DATA>;
         print;   # print $t;
      }
   }
}
__DATA__
Line 0001
Line 0002
Line 0003
Line 0004
Line 0005
Line 0006
Line 0007
Line 0008
Line 0009
Line 0010
Line 0011
Line 0012
Line 0013
Line 0014
Line 0015
Line 0016
[download]

I expected to see this:

Line 0001
Line 0002
Line 0003
Line 0004
Line 0005
Line 0011
Line 0012
Line 0013
Line 0014
Line 0015
[download]

So imagine my surprise when I saw this:

Line 0001
Line 0001
Line 0001
Line 0001
Line 0001
Line 0011
Line 0011
Line 0011
Line 0011
Line 0011
[download]

By changing the two commented lines, I get the desired output, so my program works now. But I can't rest until I know what's causing this behavior. I expect that it has something to do with the nested while and for loops and some interaction with $_.

[1] I've tried to answer it myself, but have been unsuccessful.

• I've looked over perlsyn (for for, while, and <>) and perlop (for the <> operator) to try to find a clue, but if it's in either of those, I missed it.
• I also tried a Super Search, and while I found some interesting nodes, I didn't find anything that answers my question. (I can't figure out the correct search terms, so I get far too many unrelated nodes in the results list.)

Can someone whack me with a cluestick? I'd really appreciate it...

Update: Thanks to everyone who replied. I updated my script and added it to the Code Catacombs.

...roboticus

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