...although it still leaves the "Use of uninitialized value ..." problem, which i don't quite understand.

my confusion stemmed from my bemusement with an imagined connection between the (\n) expression in the split regex and the $1 capture variable in the join and the idea that $1 must contain a newline at that point.

then it occurred to me that the intervening grep regex would undefine all the capture variables and, since it had no capturing parentheses of its own, leave them that way.

but it goes beyond that.   apparently, "capturing" parentheses in a split regex don't actually capture (at least not to the capture variables), so $1 was never defined at any point.

perl -wMstrict -e "my @ra = split /(c)/, 'abcde';
print '$1 ', defined $1 ? 'defined' : 'undefined', qq( @ra)"
$1 undefined ab c de
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