I disagree. Suggesting someone to use $a (or $b) special auto-declared (package global) variables for the purpose of avoiding the need of variable declaration with my is really poor practice.

The:

my $alpha = chr(65);
[download]

solution suggested earlier by LanX is far better.

There are a few cases where $a and $b package global variables are really useful (especially for a sort subroutine, but not only that, some other functional programming techniques can also make good use of them), please don't use them when simply declaring the variable can make what you want.