05Shell循环语句

Posted 2020-11-23 Elegant Smile

循环语句

for

语法结构

for 变量名 [ in 取值列表 ]
do
循环体
done 

注意 当for对文件内容进行逐行处理时，会忽略空行

示例

例1

ping 主机的脚本(初始版)：缺点执行过程慢，Ctrl+C只能结束某一个循环，并不能结束脚本

[root@hadoop04 shell_for]# vim ping.sh 
#!/usr/bin/bash
##########################################
# ping test                              #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################


reset_col="e[0m"
red_col="e[31m"
green_col="e[32m"

# 通过输出重定向，在ping之前清理ip_up.txt和ip_down.txt的内容
>ip_up.txt
>ip_down.txt

# 产生序列有两种方式
# {n..m}
# `seq n m`
# n<m
for i in `seq 200`
for i in `seq 200`
do
        ip=172.22.34.${i}
        ping -c1 -W1 ${ip} &> /dev/null
        if [ $? -eq 0 ];then
                echo -e "${green_col}${ip} is up${reset_col}" | tee -a ip_up.txt
        else
                echo -e "${red_col}${ip} is down${reset_col}" | tee -a ip_down.txt
        fi
done

例2

ping 主机的脚本(改进版)：每一个循环放入一个子shell中执行，可以大大地加快脚本执行的速度

注意 1.将循环放到后台运行 {}& 2.wait 3.执行脚本前清理文件内容

[root@hadoop04 shell_for]# vim ping01.sh 
#!/usr/bin/bash
##########################################
# ping test                              #
# v1.1 by ElegantSmile 9/12/2019         #
##########################################

# 通过输出重定向，在ping之前清理ip_up.txt和ip_down.txt的内容
>ip_up.txt
>ip_down.txt

reset_col="e[0m"
red_col="e[31m"
green_col="e[32m"


for i in `seq 100 200`
do
        # 将循环放到后台进程执行
        {
        ip=172.22.34.${i}
        ping -c1 -W1 ${ip} &> /dev/null
        if [ $? -eq 0 ];then
                echo -e "${green_col}${ip} is up${reset_col}" | tee -a ip_up.txt
        else
                echo -e "${red_col}${ip} is down${reset_col}" | tee -a ip_down.txt
        fi
        }&
done

#等待前面的所有后台进程结束
wait

echo "finish..."

两个版本的脚本执行时间比较

改进版

[root@hadoop04 shell_for]# time bash ping01.sh 
(略)
finish...

real    0m1.208s
user    0m0.338s
sys 0m0.781s

初始版

[root@hadoop04 shell_for]# time bash ping.sh 
(略)

real    2m16.459s
user    0m0.277s
sys 0m0.677s

例3

ping 指定主机

# 指定主机的IP地址
[root@hadoop04 shell_for]# vim ip.txt
172.22.34.18
172.22.34.89
172.22.34.56
172.22.34.192
172.22.34.94
172.22.34.243

# 编写脚本
[root@hadoop04 shell_for]# vim ping02.sh
#!/usr/bin/bash
##########################################
# ping test                              #
# v1.2 by ElegantSmile 9/12/2019         #
##########################################

ip_txt=$1

reset_col="e[0m"
red_col="e[31m"
green_col="e[32m"


for ip in `cat ${ip_txt}`
do
        {
        ping -c1 ${ip} &> /dev/null
        if [ $? -eq 0 ];then
                echo -e "${green_col}${ip} is up${reset_col}"
        else
                echo -e "${red_col}${ip} is down${reset_col}"
        fi
        }&
done

wait

echo "finish..."

# 执行脚本
[root@hadoop04 shell_for]# time bash ping02.sh ip.txt 
172.22.34.18 is up
172.22.34.56 is down
172.22.34.192 is down
172.22.34.94 is down
172.22.34.243 is down
172.22.34.89 is down
finish...

real    0m3.018s
user    0m0.008s
sys 0m0.017s

例4

创建用户，输入前缀、密码、数量；确认输入的信息；根据用户存在与否，提示已经存在或者创建用户

[root@hadoop04 shell_for]# vim create_user01.sh
!/usr/bin/bash
##########################################
# add user                               #
# v1.0 by ElegantSmile 9/12/2019         #
##########################################


while :
do
        read -p "Please enter prefix & password & num[tianyun 123 5]" prefix pass num

        printf "user information:
        --------------------------
        user prefix: ${prefix}
        user password: ${pass}
        user number: ${num}
        --------------------------
        "

        read -p "Are you sure?[y|n]: " action

        if [ "${action}" = "y" ];then
                break
        fi
done

# seq -w 等位补齐
for i in `seq -w ${num}`
do
        username=${prefix}${i}
        id ${username} &> /dev/null
        if [ $? -eq 0 ];then
                echo "user ${username} already exists"
        else
                useradd ${username}
                echo "${pass}" | passwd --stdin ${username} &> /dev/null
                if [ $? -eq 0 ];then
                        echo "user ${username} is created"
                fi
        fi
done

例5

创建用户，通过文件指定要创建的用户和密码

# 编辑用户信息文件user.txt
[root@hadoop04 shell_for]# vim user.txt 
alice  123123
jeve   7dsgf9

# 编写脚本
[root@hadoop04 shell_for]# vim create_user02.sh
#!/usr/bin/bash
##########################################
# add user                               #
# v1.1 by ElegantSmile 10/12/2019        #
##########################################


# 执行脚本时，必须传入一个参数
if [ $# -eq 0 ];then
        echo "usage: `basename $0` file"
        exit 1
fi

# 执行脚本时，必须传入一个参数
if [ $# -eq 0 ];then
        echo "usage: `basename $0` file"
        exit 1
fi

# 执行脚本时，传入的参数必须是文件
if [ ! -f $1 ];then
        echo "error file"
        exit 2
fi

# 定义变量
user_text=$1

#IFS 内部字段分隔符
 IFS=$'
'

for line in `cat "${user_text}"`
do
        # 获取指定用户的用户名和密码
        username=`echo "${line}" | awk '{print $1}'`
        userpass=`echo "${line}" | awk '{print $2}'`
        id ${username} &> /dev/null
        if [ $? -eq 0 ];then
                echo "user ${username} already exists"
                continue
        fi
        useradd ${username} &> /dev/null && echo "${userpass}" | passwd --stdin ${username} &> /dev/null
        if [ $? -eq 0 ];then
                echo "user ${username} is created"
                echo "userpassword: ${userpass}"
        fi
done

例6

批量修改主机密码

while

语法结构

while 条件测试
do
循环体
done
==当条件测试成立（条件测试为`真`），执行循环体  

注意

☆☆☆当需要对文件内容进行逐行处理时，推荐使用：

while read line

do

循环体

done < FILE

示例

例1

创建用户，通过用户列表文件创建用户

# 编辑用户信息文件user.txt
[root@hadoop04 shell_while]# vim user.txt 
alice  123123
jeve   7dsgf9

# 编写脚本
[root@hadoop04 shell_while]# vim create_user01.sh

#!/usr/bin/bash
##########################################
# add user                               #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

while read userinfo
do
        if [ ${#userinfo} -eq 0 ] ;then
                echo "Nothing to do"
                continue
        fi
        username=`echo "${userinfo}" | awk '{print $1}'`
        userpass=`echo "${userinfo}" | awk '{print $2}'`
        id "${username}" &> /dev/null
        if [ $? -eq 0 ];then
                echo "user ${username} already exists"        else    
                useradd ${username} &> /dev/null && echo "${userpass}" | passwd --stdin ${username} &> /dev/null
                if [ $? -eq 0 ];then
                        echo "user ${username} is created"
                        echo "userpassword: ${userpass}"
                        echo "username: ${username}"
                fi      
        fi

done < user.txt

echo "all ok..."

until

语法结构

until 条件测试
do
循环体
done
==当条件测试成立（条件测试为`假`），执行循环体  

示例

ping主机，检查IP状态

# while循环
# ip ping不通时提示
# 类似于下线提示
[root@hadoop04 shell_until]# vim ping01.sh 
#!/usr/bin/bash
##########################################
# ping hosts                             #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

ip=$1

while ping -c1 -W1 ${ip}&> /dev/null:
do
        sleep 1
done

echo "${ip} is down"


# until循环
# ip ping得通时提示
# 类似于上线提示
[root@hadoop04 shell_until]# vim ping02.sh 
#!/usr/bin/bash
##########################################
# ping hosts                             #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

ip=$1

until ping -c1 -W1 ${ip}&> /dev/null:
do
        sleep 1
done

echo "${ip} is up"

For While Until对比

循环次数固定的  --> for

循环次数不固定的  --> while until

对文件逐行处理  --> while

ping主机探测

循环次数固定的ping主机探测

For

[root@hadoop04 shell_for_while_until]# vim for_while_until_ping.sh 
#!/usr/bin/bash
##########################################
# ping hosts                             #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

for i in {2..254}
do
    {
    ip=172.22.145.${i}
    ping -c1 -W1 ${ip} &> /dev/null
    if [ $? -eq 0 ];then
        echo "${ip} is up"  
    fi
    } &
done

wait

echo "all finish..."

While

[root@hadoop04 shell_for_while_until]# vim while_until_for_ping.sh 
#!/usr/bin/bash
##########################################
# ping hosts                             #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

i=2

while [ $i -le 254 ]
do
    {
    ip=172.22.145.${i}
    ping -c1 -W1 ${ip} &> /dev/null
    if [ $? -eq 0 ];then
        echo "${ip} is up"  
    fi
    } &
    let i++
done

wait

echo "all finish..."

Until

[root@hadoop04 shell_for_while_until]# vim until_for_while_ping.sh 
#!/usr/bin/bash
##########################################
# ping hosts                             #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

i=2

until [ $i -gt 254 ]
do
    {
    ip=172.22.145.${i}
    ping -c1 -W1 ${ip} &> /dev/null
    if [ $? -eq 0 ];then
        echo "${ip} is up"  
    fi
    } &
    let i++
done

wait

echo "all finish..."

计算1-100的和

For

[root@hadoop04 shell_for_while_until]# vim for_while_until_sum100.sh
#!/usr/bin/bash
##########################################
# sum 100                                #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################


for i in {1..100}
do
        #let sum=${sum}+${i}
        let sum+=${i}
done

echo "sum: ${sum}"

While

[root@hadoop04 shell_for_while_until]# vim while_until_for_sum100.sh
#!/usr/bin/bash
##########################################
# sum 100                                #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

i=1

while [ ${i} -le 100 ]
do
        #let sum=${sum}+${i}
        let sum+=${i}
        let i++
done

echo "sum: ${sum}"

Until

[root@hadoop04 shell_for_while_until]# vim until_for_while_sum100.sh
#!/usr/bin/bash
##########################################
# sum 100                                #
# v1.0 by ElegantSmile 10/12/2019        #
##########################################

i=1

until [ ${i} -gt 100 ]
do
        #let sum=${sum}+${i}
        let sum+=${i}
        let i++
done

echo "sum: ${sum}"