#!/bin/bash
#
# compute n factorial using recursive function 
# (an example of recursion and use of bash arithmetic)
#
# usage:  factorial n
#
function fac() {
    n=$1
	if [ $n -le 1 ]
	then
		echo 1
	else
		echo $(( $n * $(fac $((n-1))) ))
	fi
}


if [ -z "$1" ]
then
	echo usage is $(basename $0) num
	exit 1
fi
# really ought to check here for numeric input, not less than 0

fac $1