Turn off warnings selectively and in a small scope

---

examples/advanced-perl/no_warnings.pl

#!/usr/bin/perl 
use strict;
use warnings;

my $total;

add();

print "$total\n";


sub add {
    no warnings 'uninitialized';
    $total = $total + rand();
}

See
perldoc warnings       for the use of warnings
perldoc perllexwarn    for the warning categories
perldoc perldiag       for a list of warnings and errors