netspeeds.py

#!/usr/bin/env python3
import sys
import time

try:
    _, iface = sys.argv
except ValueError:
    print("usage: {} [iface]".format(sys.argv[0]))
    sys.exit(1)

def nice(i):
    suffixes = ['B/s', 'kiB/s', 'MiB/s', 'GiB/s']
    power = 0
    while i > 1024 and power < len(suffixes) - 1:
        i /= 1024
        power += 1
    return "{:.02f} {}".format(i, suffixes[power])

lasttx = None
lastrx = None
while True:
    with open("/proc/net/dev") as f:
        for l in f.readlines():
            try:
                name, rx, _, _, _, _, _, _, _, tx, _, _, _, _, _, _, _ = l.split()
                if iface != name.rstrip(":"):
                    continue
            except ValueError:
                continue
            tx = int(tx)
            rx = int(rx)
            if lasttx and lastrx:
                print("{} in, {} out".format(*[nice(i) for i in [rx - lastrx, tx - lasttx]]))
            lasttx = tx
            lastrx = rx
    time.sleep(1)