I wrote something similar to this once. Here's the quick one-liner from my bash_history. I'm not sure if it measures the incoming or outgoing traffic on the eth0 device, because it was just a quick one-liner which I don't usually document or even save. It's using the linux proc interface instead of executing ifconfig. 

ruby -we '@s = File.open("/proc/net/dev"); @pq = (); while sleep 20; @
+s.rewind; cq = @s.readlines.find{|l|l=~/^\s*eth0/}.scan(/[^\W:]+/)[9]
+.to_i; ct = Time.now; @pq and printf "%.2f byte/sec\n", (cq-@pq)/Floa
+t(ct-@pt); @pq, @pt = cq, ct; end;'

[download]

By the way, you could also get more detailed statistics by setting up iptables rules because there's a packet and byte counter for each rule.

In reply to Re: measuring IN/OUT traffic on your computer by ambrus
in thread measuring IN/OUT traffic on your computer by spx2

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