[Linux Shell学习系列七]Bash循环——5循环控制

D15

break和continue是Bash中的循环控制命令，其用法与其他编程语言中的同名语句一致。

1. break语句

用于从for、while、until或select循环中退出、停止循环的执行。

语法：

break [n]

n代表嵌套循环的层级，如果指定了n，break退出n级嵌套循环。如果没有指定n或n<1，则退出状态码为0，否则退出状态码为n。

$ cat break.sh 
#!/bin/bash
#20200525

[ $# -eq 0 ] && { echo "Usage: $0 filepath"; exit 1; } #如果没有输入参数，则打印提示并退出

match=$1 #用位置参数获取输入
found=0

for file in ./test/*
do
        echo $file
        if [ $file == "$match" ]
        then 
                echo "The file $match was found!"
                found=1
                break #退出for循环
        fi
done

[ $found -ne 1 ] && echo "The file $match not found in ./test"


#执行
$ ./break.sh a.txt
./test/a.txt
./test/c.txt
./test/d.txt
The file a.txt not found in ./test
$ ./break.sh ./test/a.txt
./test/a.txt
The file ./test/a.txt was found!

省略P167嵌套循环示例

2. continue语句

用于跳过循环体中剩余的命令直接跳转到循环体的顶部，重新开始下一次重复。

continue语句可用于for、while或until循环。

语法：

continue [n]

示例：

$ cat continue.sh 
#!/bin/bash
#20200525

[ $# -eq 0 ] && { echo "Usage: $0 filepath"; exit 1; } #如果没有输入参数，则打印提示并退出

match=$1 #用位置参数获取输入
found=0

for file in ./test/*
do
        echo $file
        if [ $file != "$match" ]
        then 
                echo "The file $file does not match!"
                continue #不匹配时跳转到下一次循环
        fi

        found=1
        echo "The file $match was found once!"
done

[ $found -lt 1 ] && echo "The file $match not found in ./test" || echo "The file $match was found in ./test"

#执行
$ ./continue.sh ./test/c.txt
./test/a.txt
The file ./test/a.txt does not match!
./test/c.txt
The file ./test/c.txt was found once! #此处匹配，因此继续执行了下面的echo语句
./test/d.txt
The file ./test/d.txt does not match!
The file ./test/c.txt was found in ./test

$ ./continue.sh a.txt
./test/a.txt
The file ./test/a.txt does not match!
./test/c.txt
The file ./test/c.txt does not match!
./test/d.txt
The file ./test/d.txt does not match!
The file a.txt not found in ./test

省略P168的示例，以break的示例改造。

本节结束

[Linux Shell学习系列七]Bash循环——5循环控制

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