The problem is that in my $log variable i can't store the output of the script. Do you know an alternative to call a script and store the output into a variable?

Well, that uses the shell, but should work if everythings properly quoted ... inside of tk and outside of tk ... if it isn't working ddumper up the value and examine it (a technique detailed in Basic debugging checklist and brian's Guide to Solving Any Perl Problem )

Alternatives are Capture::Tiny, IPC::Run3, String::ShellQuote , Win32::ShellQuote, Proc::Background, system_detached (yes, the links are copy/paste I dont like editing too much:D)