according to the message I get when I use the 'use diagnostics' with this code.

Since Sprad was looking for better messages "for warnings like these", I think it's worthwhile to emphasize the use diagnostics pragma Sandy mentioned.

Consider this trivial case:

#!/usr/bin/perl -w

my $a = 1;
my $c = 2;
print $a + c;
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Without using diagnostics, I get this:

Unquoted string "c" may clash with future reserved word at test.pl line 5.
Argument "c" isn't numeric in addition (+) at test.pl line 5.

However, if I do use it, I get a much more informative error:

Unquoted string "c" may clash with future reserved word at test.pl line 5 (#1)

    (W reserved) You used a bareword that might someday be claimed as a reserved word.
    It's best to put such a word in quotes, or capitalize it somehow, or insert
    an underbar into it.  You might also declare it as a subroutine.

Argument "c" isn't numeric in addition (+) at test.pl line 5 (#2)

    (W numeric) The indicated string was fed as an argument to an operator that
    expected a numeric value instead.  If you're fortunate the message
    will identify which operator was so unfortunate.

Sure, in the case I've provided it isn't especially helpful, but it can be useful for tracking down more bizarre errors by giving some suggestions.