Finding total data transfer in linux machine

 sar -n DEV | gawk '{y=$4+$5}{print $0," ",y/1024}

Finding duplicate entry in a array

my %seen;
@s=qw/ a b c d e f a /;
foreach $i (@s)
{
if ( exists $seen{$i} )
{
$seen{$i}++
}
else
{
$seen{$i}=1;
}
}
foreach $i (keys %seen)
{
print "$i count $seen{$i}.\n";
}