Display realtime bandwidth usage for a given interface (Linux only)

bandwidth-usage.sh

#!/bin/bash
#
# Display the realtime bandwidth usage for the specified interface.
#
# dsimmons@squiz.co.uk
# 2011-08-03
#

# Number of seconds to average data over
avgsecs=3

if [ "$1" == "" ]; then
		echo "Usage: $0 <interface>" >&2
		echo "" >&2
		echo "Available interfaces:" >&2
		cat /proc/net/dev |cut -f1 -d':' |tail -n'+3' >&2
		exit 99
fi

# Use two arrays to store history of rx/tx total bytes transferred
declare -a hist_rx hist_tx

# Print interface name at the top
echo "$1:"

while [ 1 ]; do

		# Trim arrays to last $avgsecs secs
		while [ ${#hist_rx[*]} -gt $avgsecs ]; do
				unset hist_rx[0]
				hist_rx=("${hist_rx[@]}")
		done
		while [ ${#hist_tx[*]} -gt $avgsecs ]; do
				unset hist_tx[0]
				hist_tx=("${hist_tx[@]}")
		done

		# Get total transferred bytes
		rx_bytes_last=$rx_bytes
		tx_bytes_last=$tx_bytes
		rx_bytes=$(cat /proc/net/dev |grep "$1:" |cut -f2 -d':' |awk '{print $1}')
		tx_bytes=$(cat /proc/net/dev |grep "$1:" |cut -f2 -d':' |awk '{print $9}')

		# Skip output if this is the first run
		[ -z $rx_bytes_last ] && sleep 1 && continue

		# Calculate diff from previous run
		hist_rx[${#hist_rx[*]}]=$(($rx_bytes - $rx_bytes_last))
		hist_tx[${#hist_tx[*]}]=$(($tx_bytes - $tx_bytes_last))

		# Calculate RX average
		rx_sum=0
		for i in "${hist_rx[@]}"; do rx_sum=$(($rx_sum + $i)); done
		rx_avg=$((rx_sum / ${#hist_rx[*]}))

		# Calculate TX average
		tx_sum=0
		for i in "${hist_tx[@]}"; do tx_sum=$(($tx_sum + $i)); done
		tx_avg=$((tx_sum / ${#hist_tx[*]}))

		# Convert values to kilobytes/sec
		rx_val=$(($rx_avg / 1024))
		rx_unit="KB/s"
		tx_val=$(($tx_avg / 1024))
		tx_unit="KB/s"

		# Convert values to megabytes/sec (if >1MB)
		if [ $rx_avg -gt 1048576 ]; then
			rx_val=$(($rx_val / 1024))
			rx_unit="MB/s"
		fi
		if [ $tx_avg -gt 1048576 ]; then
			tx_val=$(($tx_val / 1024))
			tx_unit="MB/s"
		fi

		# Output data
		printf "\r    rx: %3d %4s, tx: %3d %4s" $rx_val $rx_unit $tx_val $tx_unit

		sleep 1
done