I need to prepend some code before I run my Perl script. In my prepended script I will set some debug variables and add some debugging subroutines. The easiest way I've found to do this is with the -I and -M parameters. This allows you to set an include directory, and a specific module to be loaded before your script starts.

I was able to create a debug.pm in my /tmp/ directory and prepend it to my Perl script like this:

perl -I/tmp/ -Mdebug my_script.pl

This tells Perl to add /tmp/ to the list of locations to look for modules, and then to load the module debug. Then you simply make a debug.pm that includes the global variables you want to include and your main script will be able to read them.