A not very pretty but relatively simple solution I used at least once in a similar situation, not pretty but it worked:

- my first Perl script did a number of preliminary things (reading and generating files, etc.) and then launched a shell script and then simply died;

- the shell script did the sourcing and some other needed dirty work, and then launched another Perl script which could now work with all the environment properly set up (it could actually have launched the same Perl script with different arguments, but that looked too far-fetched).

I have a reasonable experience of shell scripting, but I am really not an expert on the subject, nor on the fine details of the Unix execution environment. There might have been better ways to get the desired results, but once it worked, I did not feel like trying to fix or break it. I have actually also done something relatively similar under VMS, but that would probably get off-topic.

I did not fully understand some of the discussions in the previuous posts, I hope that I am not just proposing a solution already suggested by someone else.