#!/bin/bash
#=============== function 
function add
{
echo $(cat $@) | tr ' ' '+' | bc
}
#=============== main
if  [ $# -gt 0 ] ; then
	for item 
	do 
	   if [ ! -f $item ]
		then
			echo "ERROR: $file doesn't exist" >&2
			exit 1
	    fi
	done
	sum=$(add "$@")
else
	sum=$(add - )
fi
echo "sum = $sum"
exit 0