The info you need is in /proc/net/dev
# cat /proc/net/dev
Inter-| Receive | Transmit
face |bytes packets errs drop fifo frame compressed multicast|bytes packets errs drop fifo colls carrier compressed
lo: 177937 1304 0 0 0 0 0 0 177937 1304 0 0 0 0 0 0
eth0:16268834 14619 0 0 0 10091 0 0 1201136 10555 20 0 0 0 0 0
For the transfer rate you will have to calculate the delta from the previous capture but the value will be approximate.