Note that while it makes a best effort to determine the variable name (or array/hash subscript), that can't always be unambiguously determined: in which case it falls back to the old format:

$ perl5100 -we 'my ($x,@y); $x=$y[0]+1'
Use of uninitialized value $y[0] in addition (+) at -e line 1.

$ perl5100 -we 'my ($x,@y); $x=$y[0]+$y[1]'
Use of uninitialized value in addition (+) at -e line 1.
Use of uninitialized value in addition (+) at -e line 1.
$
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Dave