> cat 705063.pl
my $verbose = (@ARGV && $ARGV[0] eq '-v' && shift);
if (defined $verbose) {
    print "verbose:$verbose:\n";
}
else {
    print "verbose not defined\n";
}
> 
> ./705063.pl
verbose:0:
> ./705063.pl -v
verbose:-v:
> ./705063.pl -v -b -n
verbose:-v:
> ./705063.pl -b
verbose::