shell study notes 11-break, continue, exit, retrurn learning

1. Description

break (loop control), continue (circulation control), exit (exit the script), return (exit function)

Which break, continue in conditional statements and loop statements (for, while, if, etc.) control program to
which the execution state of exit and exit for all statements in the script, exit can also return to the previous program or command value to the current shell
which is similar return to exit, but only to return inside the function execution function returns a status value.

"N" is explained

command	Explanation
break n	N represents an out without the entire cycle, and n represents the number of layers out of the cycle
continue n	N represents without skip this cycle, ignoring the remaining codebook cycle, the next cycle into the circulation. n represents the n-th layer retreated continue to cycle
exit n	Exit the current shell program, n is the status of the last execution of the return value. n may be omitted, the shell next by "¥?" n receives the exit of the plant
return n	Used in the function as the function's return value to determine whether the function is executed correctly. The shell can receive the next exit n by n-plant "$?"

2, a flowchart

Break function flowchart is executed

while-break

for-break

continue functional flow diagram

while-continue

for-continue

functional flow exit

while-exit

for-exit

3, basic example

script

#!/bin/bash
if [[ $# -ne 1 ]]; then #<==如果传参数个数不为1，则打印下面的使用提示。
    #statements
    echo $"usage:0 {break|continue|exit|return}" #<==分别传入4个命令作为参数
    exit 1              #<==退出脚本
fi
test(){                 #<==定义测试函数
    for (( i = 0; i <= 5; i++ )); do
        #statements
        if [[ $i -eq 3 ]]; then
            #statements
            $*;         #<==这个地方的"$*"就是接收函数外的参数将来就是{break|continue|exit|return}中的一个
        fi
        echo $i
    done
    echo "I am in func." #<==循环外的输出提示
}
test $*                  #<==这里的”$*“为函数的传参
func_ret=$?              #<==接收并测试函数返回值
if [[ `echo $*|grep return|wc -l` -eq 1 ]]; then #<==如果传参有return
    #statements
    echo "return's exit status:$func_ret"        #<==提示return退出状态
fi
echo "ok"                                        #<==函数外的输出提示

result

Incoming break command results

[root@test1 test]# ./break1.sh 
usage:0 {break|continue|exit|return}
[root@test1 test]# ./break1.sh break
0
1
2
I am in func.  #<==循环外的输出提示
ok             #<==函数外的输出提示

See, I equals 3 and subsequent cycles is not performed, but the echo is performed outside the loop, it is performed to break out and if for outer loop, and then perform printing outside ok done statement after the for loop

Incoming continue command results

[root@test1 test]# ./break1.sh continue      
0
1
2   #<==没有3
4
5
I am in func.  #<==循环外的输出提示
ok             #<==函数外的输出提示

I can see only equal to 3 this layer is not executed, the other is performed, echo also performed outside the loop, this is the only explanation continue the termination of the "3" This cycle

Incoming exit command

[root@test1 test]# ./break1.sh exit
0
1
2

To exit the shell

Incoming return command

[root@test1 test]# ./break1.sh return
0
1
2
return's exit status:0
ok

We can see the exit function, and prompting return exit status

Incoming exit 118 and return 118

[root@test1 test]# ./break1.sh "exit 118"
0
1
2   #<==只打印了0，1，2
[root@test1 test]# echo $?
118
[root@test1 test]# ./break1.sh "return 118"
0
1
2
return's exit status:118    #<==确实将118返回到了函数的外部脚本
ok
[root@test1 test]# echo $?
0                           #<==执行脚本后的返回值还是0
[root@test1 test]#

Exit 118 can be seen to exit the loop, there is no ok output external function, the return value of the specified 118
can see the return 118, the function exits and returns the output value 118, and the output external function ok