Based on the question, I would assume your looking for the C/C++ #define method for Perl. You can find an explaination of converting C/C++ #define methods to Perl here.

Simply put, the #define used in C/C++ does not exist in Perl, atleast not in the same way. You will need to use use constant to define a fixed value. You would need it, idealy, in your Perl script head, or in a use command (in the script head), like use myheadderfile; where myheadderfile is your #define's in Perl methods with .pm for the file extension (verses .h or .hpp).

In regards to using my, in most situations my should be use, there are, however, situations where my causes the script to fail or causes incorrect output (few, but they do exist). Based on what you asked for, they should be fine, and should be used.