Arithmetic in bash is done with $ and double parentheses: echo "$(($num1+$num2))" Or $ and square brackets: echo "$[$num1+$num2]" You can assign from that (sans echo). There is also expr: echo `expr "$num1" + "$num2"`
http://unix.stackexchange.com/a/93030
bash arithmatic,布布扣,bubuko.com
原文：http://www.cnblogs.com/long123king/p/3833046.html