五、shell中的执行流控制

一、for语句

作⽤为循环执⾏动作
for语句结构
for 定义变量
do 使⽤变量，执⾏动作
done 结束标志

for语句的基本格式

[root@ansible test]# cat test.sh 
#!/bin/bash
for WESTOS in $(seq 1 2 10)
do
 echo $WESTOS
done
[root@ansible test]# sh test.sh 
1
3
5
7
9
[root@ansible test]# for name in $(seq 1 2 10); do echo $name; done
1
3
5
7
9

[root@ansible test]# for WESTOS in westos linux lee;do echo $WESTOS;done
westos
linux
lee

[root@ansible test]# for WESTOS in {10..1};do echo $WESTOS;done
10
9
8
7
6
5
4
3
2
1

[root@ansible test]# for ((WESTOS=0;WESTOS<10;WESTOS++));doecho $WESTOS;done
0
1
2
3
4
5
6
7
8
9

练习

check_host.sh
⽤此脚本检测10台与您当前主机直连主机是否⽹络通常
如果⽹络通常请显⽰主机的ip列表

[root@ansible test]# cat check_host.sh 
for IP in 172.25.254.$(seq 1 10)
do
ping 172.25.254.$IP &> /dev/null && {
      echo   172.25.254.$IP
}
done

二、条件语句

1.while…do语句

作⽤
条件为真执⾏动作

while ture
do
done

2.until…do 语句

作⽤
条件为假执⾏动作

until false
do
done

3.if语句

作⽤
多次判定条件执⾏动作

if
then
elif
then
... 
else
fi

练习

check_file.sh
please input filename: file
file is not exist
file is file
file is direcory
此脚本会⼀直询问直到⽤⼾输⼊exit为⽌

[root@ansible test]# cat check_file.sh 
while true
do
	read -p "please input filename:" FILE
	if [ $FILE = "exit" ]
	then
		echo bye!
		exit
	elif [ ! -e "$FILE" ]
	then
		echo $FILE is not exited!
	elif [ -f "$FILE" ]
	then
		echo $FILE is a file!
	elif [ -d "$FILE" ]
	then
		echo $FILE is a dir!
	fi
done

三.case

if语句判定时，是从上到下判定的，假如判定有很多，恰好最后一个才符合条件，那么效率就比别人慢，这样很不合适。现在需要点名机制，case语句是效率一样。

基本结构

case $1 in
word1|WORD1)
action1
;;
word2|WORD2)action2
;;
*)
action3
esac

示例：

[root@ansible test]# cat case.sh 
case $1 in
	haha)
	echo haha
	;;
	westos)
	echo westos
	;;
	*)
	echo error
esac

四、expect

我们写脚本的目的就是为了自动执行，但是有些命令需要输入参数才可以执行，比如ssh远程连接时，会要求输入密码，输入成功才可以执行后面的操作，有时还需要先输入yes认证完再输入密码，那这种情况怎么办呢？就需要用到expect应答脚本。

问题脚本

[root@ansible test]# cat ask.sh 
#!/bin/bash
read -p "what's your name:" NAME
read -p "How old are you: " AGE 
read -p "Which objective: " OBJ
read -p "Are you ok? " OK
echo $NAME is $AGE\'s old study $OBJ feel $OK
[root@ansible test]# sh ask.sh 
what's your name:1
How old are you: 1
Which objective: 1
Are you ok? 1
1 is 1's old study 1 feel 1
[root@ansible test]# /test/ask.sh <<EOF
> 2
> 2
> 2
> 2
> EOF
2 is 2's old study 2 feel 2

应答脚本

[root@ansible test]# cat answer.exp 
#!/usr/bin/expect
set timeout 1
set NAME [ lindex $argv 0 ]
set AGE [ lindex $argv 1 ]
set OBJ [ lindex $argv 2 ]
set FEEL [ lindex $argv 3 ]
spawn /test/ask.sh
expect {
	"name" { send "$NAME\r";exp_continue }
	"old" { send "$AGE\r";exp_continue }
	"objective" { send "$OBJ\r";exp_continue }
	"ok" { send "$FEEL\r" }
}
expect eof
[root@ansible test]# expect answer.exp 2 2 2 2
spawn /test/ask.sh
what's your name:2
How old are you: 2
Which objective: 2
Are you ok? 2
2 is 2's old study 2 feel 2

转载解释很清楚的博客

五、break,continue,exit

contiue      终⽌当此次前循环提前进⼊下个循环
break        终⽌当前所在语句所有动作进⾏语句外的其他动作
exit         脚本退出

原本输出：

[root@ansible test]# cat jiajiren.sh 
for NUM in {1..10}
do
	if [ "$SUM" = "4" ]
	then
		echo jiajiren is handsome
	fi
	echo $NUM
done
echo complete

exit

break:

continue: