However this also means, that only certain variables are used in certain parts of the overall program, and that -w fills up my error_log with 'Use of uninitialized value'.

I'm a little confused by what you're saying here. If you're getting the "unititialized value" error then you are using those variables without assigning a value to them first. This is often a source of hard to track down bugs in your code - which is why -w identifies them.

"Perl makes the fun jobs fun
and the boring jobs bearable" - me