G'day jwkrahn,

It's a common mistake to forget, or not realise, that "&&" has a higher precedence than "=" which, in turn, has a higher precedence than "and". See "perlop: Operator Precedence and Associativity" (there's a table at the end of that section which lists the order of precedence).

Changing "and" to "&&" gets rid of the warning; however, in this instance, that's probably not what you want. Compare these two:

$ perl -MO=Deparse,-p -e '($used_options{ $1 } = 1 and "\${$1}")'
(($used_options{$1} = 1) and ("\${$1}"));

$ perl -MO=Deparse,-p -e '($used_options{ $1 } = 1 && "\${$1}")'
($used_options{$1} = "\${$1}");
[download]