use Net::IP;
my @sn_array = qw( 172.22.0.0/30 7.3.1.0/24 );

...

for my $net (map {new Net::IP $_}  @sn_array) {  
	do {
		$manager->start and next;
		my $p = Net::Ping->new("icmp");
		my $host = $net->ip;
		print "pinging $host\n";
		if ($p->ping($host)){
			open PingFile, ">>", "$pingable" or die $!;
			flock(PingFile, LOCK_EX);
			print PingFile "$host\n";
			flock(PingFile, LOCK_UN);
			close(PingFile);
		}
		$manager->finish;
	} while (++$net);
}