There are lots of ways of doing that. First take a look at: this info about CIDR blocks.

sub range_from_net {
   my ($subnet,$mask)=@_;
   my $subbits=addr2bits($subnet);
   my $maskbits=addr2bits($mask);
   my $allones = ~ $maskbits;
   my $top = $allones - 1;
   my $bottom = ($subbits + 1) & $allones;
   return ($bottom,$top);
}
sub addr2bits {
   my $ip=shift;
   my @o=split([\.],$ip);
   return ( ($o[0] << 24 ) + ($o[1] << 16) + ($o[2]<<8) + $o[3]);
}

sub bits2addr {
   my $bits=shift;
   return sprintf("%d.%d.%d.%d",
                  (($bits & 0xff000000 ) >> 24),
                  (($bits & 0x00ff0000 ) >> 16),
                  (($bits & 0x0000ff00 ) >> 8),
                   ($bits & 0x000000ff ) );
}
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There may be a few bugs in the above code as I did not test it, but there is the basic overall algorithm I have used when I have had to solve the problem.

---

Peter L. Berghold -- Unix Professional Peter at Berghold dot Net
	Dog trainer, dog agility exhibitor, brewer of fine Belgian style ales. Happiness is a warm, tired, contented dog curled up at your side and a good Belgian ale in your chalice.