#!/bin/bash
# http://en.wikipedia.org/wiki/European_Article_Number
oe="13"
while read line; do
for (( j=0; j<${#line}; j++ )); do
chk=$((chk+${line:$j:1}*${oe:$j%2:1}))
done
[[ $((chk%10)) == 0 ]] && digit=0 || digit=$((10-chk%10))
chk=0
echo ${line}${digit}
done