Is that "for" loop syntax something that was introduced with 5.10? I tried that script with 5.8.8 and had two problems with it. First, the snippet as you posted it gave me this sort of error:

$ perl -e 'use strict; for my ($d,$v){ $_=lc<>; chomp; }
   print "got $d and $v\n"'
Missing $ on loop variable at -e line 1.
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I could get rid of that with an extra set of parens, but then there were scoping issues, because the two variables were limited to the scope of the "for" loop:

$ perl -e 'use strict; for (my($d,$v)){ $_=lc<>; chomp; }
   print "got $d and $v\n"'
Global symbol "$d" requires explicit package name at -e line 2.
Global symbol "$v" requires explicit package name at -e line 2.
Execution of -e aborted due to compilation errors.
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Interestingly, neither of those problems seems to affect GrandFather's snippet -- the following not only compiles, but when you feed it data, it does what it's supposed to do:

$ perl -e 'use strict; ($_=lc <>), chomp for my ($d,$v);
  print "got $d and $v\n"'
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Again, I'm only looking at 5.8.8 -- it would be good to know whether 5.10 has different behavior in this regard.