linux shell脚本 判断变量是否是数字，数字加减

变量的加减

num=$((num1 + num2))
num=$(($num1 + $num2))       # Also works
num=$((num1 + 2 + 3))        # ...
num=$[num1+num2]             # Old, deprecated arithmetic expression syntax

判断 变量是否是数字

re='^[0-9]+$'
if ! [[ $yournumber =~ $re ]] ; then
   echo "error: Not a number" >&2; exit 1
fi