The following shell script shows current download and upload speeds for the network interface you choose.
Copy the shell script in a file named, i.e: net_speed.sh
Then after setting execution permissions:
chmod a+x net_speed.sh
You can run the shell script passing as the first argument the network interface you want to monitor:
./net_speed.sh eth0
You will get a line like that:
eth0 DOWN:15 KB/s UP:880 B/s
This script works parsing /proc/net/dev file and calculating the difference between current transmitted or received bytes and their values one second ago.
#!/bin/bash
# This shell script shows the network speed, both received and transmitted.
# Usage: net_speed.sh interface
# e.g: net_speed.sh eth0
# Global variables
interface=$1
received_bytes=""
old_received_bytes=""
transmitted_bytes=""
old_transmitted_bytes=""
# This function parses /proc/net/dev file searching for a line containing $interface data.
# Within that line, the first and ninth numbers after ':' are respectively the received and transmited bytes.
get_bytes()
{
line=$(cat /proc/net/dev | grep $interface | cut -d ':' -f 2 | awk '{print "received_bytes="$1, "transmitted_bytes="$9}')
eval $line
}
# Function which calculates the speed using actual and old byte number.
# Speed is shown in KByte per second when greater or equal than 1 KByte per second.
# This function should be called each second.
get_velocity()
{
value=$1
old_value=$2
let vel=$value-$old_value
let velKB=$vel/1024
if [ $velKB != 0 ];
then
echo -n "$velKB KB/s";
else
echo -n "$vel B/s";
fi
}
# Gets initial values.
get_bytes
old_received_bytes=$received_bytes
old_transmitted_bytes=$transmitted_bytes
# Shows a message and waits for one second.
echo "Starting...";
sleep 1;
echo "";
# Main loop. It will repeat forever.
while true;
do
# Get new transmitted and received byte number values.
get_bytes
# Calculates speeds.
vel_recv=$(get_velocity $received_bytes $old_received_bytes)
vel_trans=$(get_velocity $transmitted_bytes $old_transmitted_bytes)
# Shows results in the console.
echo -en "$interface DOWN:$vel_recv\tUP:$vel_trans\r"
# Update old values to perform new calculations.
old_received_bytes=$received_bytes
old_transmitted_bytes=$transmitted_bytes
# Waits one second.
sleep 1;
done
Source : Linux Clues