If you have "use warnings;" in your code (or run with "perl -w"), you should get the warning:
Reference found where even-sized list expected
If you don't have "use warnings;", then
put it in before asking a question. The warnings are there to help you, not annoy you.
UPDATE: And, if the warning is a little obscure, which in this case it is if you haven't seen it before, you can also "use diagnostics;". For example, perl -Mdiagnostics -w pm602312.pl gives:
Reference found where even-sized list expected at pm602312.pl line 2
(W misc) You gave a single reference where Perl was expecting a list
with an even number of elements (for assignment to a hash). This usua
+lly
means that you used the anon hash constructor when you meant to use
parens. In any case, a hash requires key/value pairs.
%hash = { one => 1, two => 2, }; # WRONG
%hash = [ qw/ an anon array / ]; # WRONG
%hash = ( one => 1, two => 2, ); # right
%hash = qw( one 1 two 2 ); # also fine