To turn off or on certain classes of warnings, give them as a list after the use or no warnings. So, in this case, to just turn off the warning about qw but leave the others untouched, you would write:
no warnings "qw"; my @a = qw(one , two , three , four); } my @b = qw(one , two , three , four);
The categories of warnings you can turn on and off are organized hierarchically as follows, and the warnings they cover are detailed in the perldiag documentation:
First, we'll look at the variables. When use strict is applied, a variable must either be declared lexically (using my $var) and belong to a block or file, or be declared globally, to be available in every part of the program. You can do this either by using our $var (in the same way as my) or by specifying its full name, $main::var. We'll see where the main comes from in the next chapter.
Strict on Variables
You should also know by now that use strict forces you to declare your variables before using them. In fact, it controls three areas of your programming: variables, references, and subroutines.