嵌套循环

模仿一个嵌套循环，看下输出，就知道嵌套循环的规律，一般程序中的循环都是这样，必须的。

#!/bin/bash
outer=1
for i in 1 2 3
do
echo "pass $outer in outer loop"
inner=1
for i in 1 2 3 4 5
do
echo "pass $inner in inner loop"
let "inner+=1"
done
let "outer+=1"
echo "----------------"
done

输出

pass 1 in outer loop
pass 1 in inner loop
pass 2 in inner loop
pass 3 in inner loop
pass 4 in inner loop
pass 5 in inner loop
----------------
pass 2 in outer loop
pass 1 in inner loop
pass 2 in inner loop
pass 3 in inner loop
pass 4 in inner loop
pass 5 in inner loop
----------------
pass 3 in outer loop
pass 1 in inner loop
pass 2 in inner loop
pass 3 in inner loop
pass 4 in inner loop
pass 5 in inner loop
----------------

根据输出，可以看出:嵌套循环就是在一个循环中还有一个循环,内部循环在外部循环体中.在外部循环的每次执行过
程中都会触发内部循环,直到内部循环执行结束.外部循环执行了多少次,内部循环就完成多少
次.