#!/bin/sh
# (c) Steve Parker
# http://steve-parker.org/sh/sh.shtml

# Ugh, the shell doesn't really do maths.
# We can co-opt bc or expr to do the job for us
# bc is the better option, especially when we
# involve decimal places.

litres_to_gallons()
{
  echo "$1 * 0.22" | bc
}

mpg()
{
  echo "$1 / $2" | bc
}

usage()
{
  echo "Usage: `basename $0` litres miles"
  echo
  echo "Will convert 'I used x litres to drive y miles' into an MPG figure"
  exit 1
}

# Script starts here

if [ "$#" -ne "2" ]; then
  usage
fi

gallons=`litres_to_gallons $1`
miles=$2

milespergallon=`mpg $miles $gallons`

echo "MPG for $1 litres ($gallons gallons) over $miles miles = $milespergallon mpg"