You're using words like 'subroutine' but you seem to imply that you are returning your values via exit and $@, which tells me you're evaling code instead of calling it as a straightforward subroutine.

If this is the case, your 'exit' return value isn't going to magically appear in $@. You'll need to examine the value of $? if you want to do it that way (but be warned, the value of this will need to be << 8'd to get at the number you passed to exit).

sub some_sub {
   ...
   return 5;             # not 'exit', as this terminates the script
}

$returned = &some_sub;   # 5

eval "exit(&some_sub)";  # exits block with return value of 5
$returned = $? << 8;     # 5
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Obviously, the first method is far more efficient and practical than evaluating code. I hope I'm not misunderstanding what you're doing here. You may be interested in perlsub and documentation for eval and perlvar (for $? and $@).