ifstat.sh is a shell command to report network interface usage, like vmstat/iostat do for other system counters. It works by printing the current speed at regular intervals. It has several options to configure it, and features a summary display of the measured network activity when it stops.
ifstat.sh is an ifstat alternative completely written in bash. I created it in 2011 because I knew no other way to monitor current network speed in real time.
I know this is not the best code one could write, not even on bash (I have better examples over there). I did it when I was still learning basic programming, and it is written and documented in Spanish (my native language).
But I find ifstat.sh very useful, I use it frequently, and it is very stable and complete. Also, I am proud to have developed something like this given the limited programming knowledge I had then. So, I have uploaded it here hoping it might be as useful for someone as it is for me.