use strict;
use warnings;
use Net::SNMP;
use Nagios::Plugin;
use nagios::Plugin::Getopt;

my $memRealTotalOID = '.1.3.6.1.4.1.2021.4.5.0';
my $memRealFreeOID = '.1.3.6.1.4.1.2021.4.6.0';
my $memRealCachedOID = '.1.3.6.1.4.1.2021.4.15.0';
my $memRealBuffersOID = '.1.3.6.1.4.1.2021.4.14.0';

   my ($session, $error) = Net::SNMP->session(
      -hostname  => shift || '192.168.1.1',
      -community => shift || 'private',
   );

   if (!defined $session) {
      printf "ERROR: %s.\n", $error;
      exit 1;
   }

   my $memRealFree = $session->get_request(-varbindlist => [ $memRealFreeOID],);
   my $memRealTotal = $session->get_request(-varbindlist => [ $memRealTotalOID],);
   my $memRealCached = $session->get_request(-varbindlist => [ $memRealCachedOID],);
   my $memRealBuffers = $session->get_request(-varbindlist => [ $memRealBuffersOID],);
   
   my $buffers = $memRealBuffers->{$memRealBuffersOID}; 
   my $cache = $memRealCached->{$memRealCachedOID};
   my $total=  $memRealTotal->{$memRealTotalOID};
   my $free = $memRealFree->{$memRealFreeOID};
   
   my $memRealUsed = $total - $free;
  
   
  my $realPercent = (($memRealUsed - $buffers - $cache)/ $total) * 100;