# Bytes Receive
ifconfig eth0 | awk '/RX bytes/ {print $2}' | awk -F: '{print $2}'

# Bytes Transmitted
ifconfig eth0 | awk '/RX bytes/ {print $6}' | awk -F: '{print $2}'

# A human readable output
ifconfig eth0 | awk '/RX bytes/ {print $3, $4}' # Received
ifconfig eth0 | awk '/RX bytes/ {print $7, $8}' # Transmitted