If you want to get the output from a shell command, use backticks or the qx form of quotation.
my $todayDate = qx(date);
my ( $day, $month, $dayNum ) = split ' ', $todayDate;
print "the day will be $day\n";
print "the month will be $month\n";
print "the day num will be $dayNum\n";
the day will be Tue
the month will be Nov
the day num will be 10
As others have noted, this may not be the best way to get the date and time, but it is how to do what you were trying to do. Note that what's returned will typically have a newline at the end, and it behaves differently in list context.
For the full scoop on qx, see perlop in the section "Quote and Quote-like Operators".