..or use the already available Linux::net::dev:

$ perl
use strict;
use warnings;
use Linux::net::dev;
use Data::Dumper;

my $devs = Linux::net::dev::info();
foreach my $key (keys %$devs) {
  print $key . ": ". Dumper($devs->{$key}) if ($key eq q{eth0});
}
__END__
eth0: $VAR1 = {
          'rcompressed' => '0',
          'tbytes' => '500984059',
          'rpackets' => '2007663',
          'tfifo' => '0',
          'rfifo' => '0',
          'terrs' => '0',
          'rmulticast' => '0',
          'tdrop' => '0',
          'tpackets' => '1283040',
          'rdrop' => '0',
          'rframe' => '0',
          'tcolls' => '0',
          'tcarrier' => '0',
          'tcompressed' => '0',
          'rerrs' => '0',
          'rbytes' => '1500560631'
        };
[download]