break n层循环的理解

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在学习Shell脚本的break与continue语句时，有一些困惑，就是break n可以跳出几层循环的问题，continue也是如此。不过弄懂了break n的问题，continue n的问题应该也清楚了。

第一步：break 1。

新建一个loop.sh脚本，输入以下代码：

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#!/bin/bash
for ((m=1;m<=2;m++))
do
   for((j=1;j<=3;j++))
        do
            for ((i=1;i<=4;i++))
                do
                    if [ $i -eq 3 ]
                    then
                       break 1
                    fi
                    echo "The m cycle is $m the out cycle is $j,and inner cycle is $i"
                done
         done
done

运行结果，如下所示：

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biotest@ubuntu:~/loop$ bash loop.sh 
The m cycle is 1 the out cycle is 1,and inner cycle is 1
The m cycle is 1 the out cycle is 1,and inner cycle is 2
The m cycle is 1 the out cycle is 2,and inner cycle is 1
The m cycle is 1 the out cycle is 2,and inner cycle is 2
The m cycle is 1 the out cycle is 3,and inner cycle is 1
The m cycle is 1 the out cycle is 3,and inner cycle is 2
The m cycle is 2 the out cycle is 1,and inner cycle is 1
The m cycle is 2 the out cycle is 1,and inner cycle is 2
The m cycle is 2 the out cycle is 2,and inner cycle is 1
The m cycle is 2 the out cycle is 2,and inner cycle is 2
The m cycle is 2 the out cycle is 3,and inner cycle is 1
The m cycle is 2 the out cycle is 3,and inner cycle is 2

第二步：break 2。

现在将break 1改为break 2，运行，如下所示：

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#!/bin/bash
for ((m=1;m<=2;m++))
do
   for((j=1;j<=3;j++))
        do
            for ((i=1;i<=4;i++))
                do
                    if [ $i -eq 3 ]
                    then
                       break 2
                    fi
                    echo "The m cycle is $m the out cycle is $j,and inner cycle is $i"
                done
         done
done

运行：

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biotest@ubuntu:~/loop$ bash loop.sh 
The m cycle is 1 the out cycle is 1,and inner cycle is 1
The m cycle is 1 the out cycle is 1,and inner cycle is 2
The m cycle is 2 the out cycle is 1,and inner cycle is 1
The m cycle is 2 the out cycle is 1,and inner cycle is 2

第三步，break 3。

现在将break 2改为break 3，如下所示：

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#!/bin/bash
for ((m=1;m<=2;m++))
do
   for((j=1;j<=3;j++))
        do
            for ((i=1;i<=4;i++))
                do
                    if [ $i -eq 3 ]
                    then
                       break 3
                    fi
                    echo "The m cycle is $m the out cycle is $j,and inner cycle is $i"
                done
         done
done

运行，如下所示：

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biotest@ubuntu:~/loop$ bash loop.sh 
The m cycle is 1 the out cycle is 1,and inner cycle is 1
The m cycle is 1 the out cycle is 1,and inner cycle is 2

从上面的结果可以看出来：①最内层的是第1层循环，再次是第2层循环，最外层就是第3层循环。