Thanks for the pointer but as far as I can see removing the -w commandline option and introducing use warnings 'all'; should not result in more warnings as I understand the command line option is more 'crude' where the use warnings allows for more fine-tuning?

Or am I wrong here?

Anyway, at least when compiling the code I do not get more warnings then before (basically none as I do not want any warning to show up when the programs run - and basically till now I was able to keep it like this).
I will check it again on runtime after introducing these changes.