Check what the active network interface speed is on Linux

Linux command to print out the active speed (in MBit/sec) of the primary (IPv4) physical network interface (non-wireless).

ip -o -4 route show to default | awk '{print "/sys/class/net/"$5"/speed"}' | xargs cat

Note: this won’t work for wireless interfaces, and virtual interfaces (i.e. many VPSs) will incorrectly show -1 for this, it’s only reliable for reporting on physical network interfaces.