linux命令SHELL编程：数若大于0则输出该数；若小于或等于0则输出0值的程序怎么写？

#!/bin/bash\x0d\x0aecho "Please input a number："\x0d\x0a#键盘读取赋值给变量num\x0d\x0aread num\x0d\x0a#判断num的值是否为数字，条件否则直接退出\x0d\x0aexpr $num + 0 1>/dev/null 2>&1\x0d\x0aif [ $? -ne 0 ]\x0d\x0athen\x0d\x0aecho "${num} is not a number!"\x0d\x0aexit 0\x0d\x0afi\x0d\x0a#判断变量num的值是否大于0\x0d\x0aif [ "$num" -gt 0 ]\x0d\x0athen\x0d\x0aecho $num\x0d\x0aelse\x0d\x0aecho 0\x0d\x0afi