netspeed.sh

#!/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