"calling system inside or outside a method call can not affect is behaviour in any way"
Yes, that's why I am posting it here

"Have you checked that you are calling the external program with the right arguments? try replacing the command by "echo" and see what is printed. "
Of course, I did these multiple times. As I said it does work with & at the end.

"Maybe the program you are calling is waiting for some input from stdin, maybe $param is undef... "
Nope, it's all correct (no stdin input) otherwise it won't work with & also!


10x for your attention :)