As NetWallah suggested, using a CPAN module will be best. Below is an example for using Net::IP. It would replace the @sn_array assignment and the "foreach $host" loop in the original code

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);
}
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