循环语句for基本概述
01. for循环基础语法
for 变量名 in [ 取值列表 ]do 循环体done
02. for循环基本使用示例
#取值列表有多种取值方式，可以直接读取in后面的值，默认以空格做分割符
[root@qiudao /scripts]# cat for-1.sh #!/bin/bash for var in file1 file2 file3do echo "The text is $var" done [root@qiudao /scripts]# sh for-1.sh The text is file1 The text is file2 The text is file3
03. for循环基本使用示例，列表中的复杂值，可以使用引号或转义字符""来加以约束
[root@qiudao /scripts]# cat for-2.sh #!/bin/bash for var in file1 "file2 hello" file3 do echo "The text is $var" done [root@qiudao /scripts]# sh for-2.sh The text is file1 The text is file2 hello The text is file3 #转义字符 [root@qiudao /scripts]# cat for-3.sh #!/bin/bash for var in file1 file \'2 do echo "The text is $var" done [root@qiudao /scripts]# sh for-3.sh The text is file1 The text is file The text is '2
04. for循环基本使用示例，从变量中取值
[root@qiudao /scripts]# cat for-4.sh #!/bin/bash list="file1 file2 file3" for var in $list do echo $var done [root@qiudao /scripts]# sh for-4.sh file1 file2 file3
05. for循环基本使用示例，从命令中取值
[root@qiudao /scripts]# cat for-5.sh #!/bin/bash for var in `cat /etc/hosts` do echo $var done [root@qiudao /scripts]# sh for-5.sh 127.0.0.1localhostlocalhost.localdomainlocalhost4localhost4.localdomain4::1localhostlocalhost.localdomainlocalhost6localhost6.localdomain6
06. for循环基本使用示例，自定义Shell分隔符。默认情况以空格为分隔符。通过IFS来自定义分隔符
#以冒号做分隔符 IFS=: #以冒号，分号和双引号作为字段分隔符 IFS=:;" #以换行符作为字段分隔符 IFS=$'\n' #以回车为换行符 [root@qiudao /scripts]# cat for-6.sh #!/bin/bash IFS=$'\n' for var in `cat /etc/hosts` do echo $var done [root@qiudao /scripts]# sh for-6.sh 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 #以:为分隔符 [root@qiudao /scripts]# cat for-7.sh #!/bin/bash IFS=: list=`head -1 /etc/passwd` for var in $list do echo $var done [root@qiudao /scripts]# sh for-7.sh root x 0 0 root /root /bin/bash
07. for循环基本使用示例，C语言风格的for
#语法格式for ((i=0;i<10;i++))do commandsdone
#例1，单个变量，输出1到10之间的数字[root@qiudao /scripts]# cat for-8.sh#!/bin/bashfor ((i=0;i<10;i++))doecho num is $idone
[root@qiudao /scripts]# sh for-8.shnum is 0num is 1num is 2num is 3num is 4num is 5num is 6num is 7num is 8num is 9
例2，多个变量，同时输出1-9的升序和降序
解法一：
[root@qiudao /scripts]# cat for-9.sh
#!/bin/bash for ((a=1,b=9;a<10;a++,b--)) do echo num is $a $b done [root@qiudao /scripts]# sh for-9.sh num is 1 9 num is 2 8 num is 3 7 num is 4 6 num is 5 5 num is 6 4 num is 7 3 num is 8 2 num is 9 1 #解法二： [root@qiudao /scripts]# cat for-10.sh #!/bin/bash a=0 b=10 for i in {1..9} do let a++; let b--; echo num is $a $b done [root@qiudao /scripts]# sh for-10.sh num is 1 9 num is 2 8 num is 3 7 num is 4 6 num is 5 5 num is 6 4 num is 7 3 num is 8 2 num is 9 1 2. 循环语句for场景示例
01. for循环场景示例一：通过读入文件中的用户，进行批量添加用户。
[root@qiudao /scripts]# cat for-11.sh #!/usr/bin/bash for i in $(cat user.txt) do useradd $i &>/dev/null if [ $? -eq 0 ];then echo $i 用户创建成功 else echo $i 用户已存在 fi done [root@qiudao /scripts]# sh for-11.shtt1 用户创建成功tt2 用户创建成功tt3 用户创建成功tt4 用户创建成功tt5 用户创建成功tt6 用户创建成功tt7 用户创建成功tt8 用户创建成功tt9 用户创建成功tt10 用户创建成功
02. for循环场景示例二：通过读入文件中的用户:密码，进行批量添加用户。
[root@qiudao /scripts]# cat user.txt user01:suibian user02:suibian2 user03:suibian3 [root@qiudao /scripts]# cat for-12.sh #!/usr/bin/bash for i in $(cat user.txt) do #1.取出来的行，使用awk进行分隔，然后分别赋值给user和pass两个变量 user=$(echo $i|awk -F ":" '{print $1}') pass=$(echo $i|awk -F ":" '{print $2}') #2.判断用户是否存在 id $user &>/dev/null #3.用户存在则提示已存在，否则添加用户，然后使用pass变量设定对应的密码 if [ $? -eq 0 ];then echo "$user 已存在" else useradd $user echo "$pass" | passwd --stdin $user &>/dev/null echo "用户$user 创建成功！" fi done [root@qiudao /scripts]# sh for-12.sh 用户user1 创建成功！ 用户user2 创建成功！ 用户user3 创建成功！ 03. for循环场景示例三：批量创建用户脚本，需要用户输入创建的用户数量，以及需要用户输入创建的前缀。
[root@qiudao /scripts]# cat for-13.sh #!/usr/bin/bash read -p "请输入你要创建的用户前缀: " user_qz read -p "请输入你要创建的用户数量: " user_num echo "你创建的用户是 ${user_qz}1 ..${user_qz}${user_num}" read -p "你确定要创建以上用户吗？[ y/n ] " readly case $readly in y) for i in $(seq $user_num) do user=${user_qz}${i} id $user &>/dev/null if [ $? -eq 0 ];then echo "useradd: user $user already exists" else useradd $user echo "useradd: user $user add successfully." fi done ;; n) echo "你想好了再创建......" exit ;; *) echo "请不要乱输入...." exit esac 04. for循环场景示例四：批量创建用户脚本，需要用户输入创建的用户数量(必须是整数)，同时还需要用户输入前缀(前缀不能为空)。例如:前缀qls，个数10，代表创建qls1~qls10，总共10个用户。注意：此脚本仅root可执行，其他人无权限执行。
[root@qiudao /scripts]# cat for-14.sh#!/usr/bin/bashif [ ! $UID -eq 0 ] && [ ! $USER == "root" ];then echo "无权限执行......" exitfi read -p "请输入你要创建的用户前缀: " user_qzif [ -z $user_qz ];then echo "请输入有效的值....." exitfi read -p "请输入你要创建的用户数量: " user_numif [[ ! $user_num =~ ^[0-9]+$ ]];then echo "请输入整数" exitfi echo "你创建的用户是 ${user_qz}1 ..${user_qz}${user_num}"read -p "你确定要创建以上用户吗？[ y/n ] " readly case $readly in y|yes|YES) for i in $(seq $user_num) do user=${user_qz}${i} id $user &>/dev/null if [ $? -eq 0 ];then echo "useradd: user $user already exists" else useradd $user echo "useradd: user $user add successfully." fi done ;; n|no|NO) echo "你想好了再创建......" exit ;; *) echo "请不要乱输！" exitesac 05. for循环场景示例五：批量创建用户脚本，需要用户输入创建的用户数量(必须是整数)，同时还需要用户输入前缀(前缀不能为空)。例如:前缀qls，个数10，代表创建qls1~qls10，总共10个用户。注意：此脚本仅root可执行，其他人无权限执行。用户的密码使用随机密码，并保存到某一个指定的文件中。
[root@backup scripts]# cat 3.sh #!/bin/bash if [ ! $USER == "root" ] && [ ! $UID -eq 0 ];then echo "该用户没有执行权限" exit fi read -p "请输入你想要的前缀：" dir if [ -z $dir ];then echo " 输入不能为空，不支持" exit fi if [[ ! $dir =~ ^[a-Z]+$ ]];then echo "输入错误，请输入字母：" exit fi read -p "请输入创建用户的数量：" num if [ -z $num ];then echo "不能为空" exit else if [[ ! $num =~ ^[0-9]+$ ]];then echo "请输入数字为整数" exit fi fi read -p "你创建的用户为${dir}1..${dir}n${num},确认创建[y|n]: " rc case $rc in y|Y|yes) for i in $(seq $num) do user=${dir}${num} pass=$(echo $((RANDOM)) |md5sum |cut -c 2-24) id $user &>/dev/null if [ $? -eq 0 ];then echo "用户已经存在" else useradd $user &>/dev/null && echo $pass |passwd --stdin $user &>/dev/null if [ $? -eq 0 ];then echo "用户$user 创建成功，密码ok" echo "用户：$user 密码：$pass" >>/tmp/q.txt echo "用户密码文件在/tmp/q.txt" else echo "用户创建失败" exit fi fi done ;; n|N|no) echo "你不想创建，推迟" exit ;; *) echo "请输入正确的格式[y|n]" exit esac 06. for循环场景示例六：批量删除（用户需要输入用户前缀及数字），有就删除，没有就提示没有该用户。
[root@backup scripts]# cat 4.sh #!/bin/bash if [ ! $USER == "root" ] && [ ! $UID -eq 0 ];then echo "该用户没有执行权限" exit fi read -p "请输入你想要删除的前缀：" dir if [ -z $dir ];then echo " 输入不能为空，不支持" exit fi if [[ ! $dir =~ ^[a-Z]+$ ]];then echo "输入错误，请输入字母：" exit fi read -p "请输入想要删除用户的数量：" num if [ -z $num ];then echo "不能为空" exit else if [[ ! $num =~ ^[0-9]+$ ]];then echo "请输入数字为整数" exit fi fi read -p "你删除的用户为${dir}${num},确认删除[y|n]: " rc case $rc in y|Y|yes) for i in ${dir}${num} do user=${dir}${num} id $user &>/dev/null if [ $? -eq 0 ];then userdel $user &>/dev/null if [ $? -eq 0 ];then echo "用户$user已删除" else echo "用户$user删除失败" fi else echo "用户不存在" exit fi done ;; n|N|no) echo "你不想删除，退出" exit ;; *) echo "请输入正确的格式[y|n]" exit esac 07. for循环场景示例七：批量探测主机存活状态及22端口状态
1）需要用循环，循环254次2）探测主机使用ping命令
[root@backup scripts]# cat 5.sh #!/bin/bash for i in {30..50} do ip=172.16.1.$i ping -c 1 -w 1 $ip &>/dev/null if [ $? -eq 0 ];then echo "$ip是接通的" else echo "$ip是不接通的" fi done 08. for循环场景示例八：编写一个上课随机点名脚本。
1.需要有名字2.需要循环的打印这些名单3.随机挑选一个数字进行打印
[root@backup scripts]# cat student.sh #!/bin/bash stu_num=`wc -l student.txt|awk '{print $1}'` for i in $(seq $stu_num) do num=$(echo $(( $RANDOM % ${stu_num} +1 ))) sed -n "${num}p" student.txt sleep 0.2 done stu_name=$(sed -n "${num}p" student.txt) echo -e "天选之子： \033[32m ${stu_name}....\033[0m" 09. for循环场景示例九：使用for循环实现数据库的分库分表备份。
[root@backup scripts]# cat mysql.sh #!/bin/bash ############################################################## # File Name: mysql.sh # Time: 2019-10-22-15:23:08 # Author: qls # Organization: www.increase93.com ############################################################## db_user=root db_name=`mysql -uroot -e "show databases;"|sed 1d|grep -v .*_schema` date=`date +%F` for database in $db_name do if [ ! -d /backup/$database ];then mkdir -p /backup/$database fi mysqldump -u$db_user -B $database >/backup/$database/${database}_${date}.sql &>/dev/null if [ $? -eq 0 ];then echo "$database备份成功" db_table=$(mysql -u$db_user -e "use $database;show tables;"|sed 1d) for tables in $db_table do mysqldump -u$db_user $database $tables >/backup/$database/${database}_${tables}_${date}.sql if [ $? -eq 0 ];then echo "$db_table表备份成功" else echo "$db_table表备份失败" continue fi done else echo "数据库$database备份失败" continue fi done 1.怎么备份数据库 mysqldump -uroot -p123.com --single-transaction -B world > world_database.sql2.怎么备份数据库的表mysqldump -uroot -p123.com --single-transaction world city > world_city_tables.sql3.备份到哪儿/mysql_dump/oldboy/city_2019_07_16.sql #!/usr/bin/bash db_name=$(mysql -uroot -p123.com -e "show databases;"|sed 1d |grep -v ".*_schema") DB_User=root DB_Pass=123.com Date=$(date +%F) for database_name in $db_name do #1.准备每个库的目录 DB_Path=/mysql_dump/$database_name if [ ! -d $DB_Path ];then mkdir -p $DB_Path fi #2.备份数据库 mysqldump -u$DB_User -p$DB_Pass --single-transaction -B $database_name > $DB_Path/${database_name}_${Date}.sql echo -e "\033[31m $database_name 数据库 已经备份完成..... \033[0m" #3.备份数据库的每一个表 tb_name=$(mysql -u$DB_User -p$DB_Pass -e "use ${database_name};show tables;"|sed 1d) #4.批量的备份数据库的表 for table_name in $tb_name do #5.备份数据库的表数据 mysqldump -u$DB_User -p$DB_Pass --si 10. for循环场景示例十：用于判断mysql数据库主从的脚本，需要邮件通知。
1.判断io线程和sql线程是否都为yes，如果是则成功。2.如果io线程失败，则直接邮件通知，如果sql线程失败，则检查是什么错误状态码，根据状态码修复。3.无法修复，或任何错误代码太复杂建议，直接发邮件通知管理员。 [root@qiudao /scripts]# cat for-20.sh #!/usr/bin/bash IO_Status=$(mysql -uroot -p123.com -e "show slave status\G"|awk '/Slave_IO_Running/ {print $2}') SQL_Status=$(mysql -uroot -p123.com -e "show slave status\G"|awk '/Slave_SQL_Running/ {print $2}') slave_sql_error_message(){ mysql -uroot -p123.com -e "show slave status\G"|grep "Last_SQL" > /tmp/sql_err.log mail -s "MySQL Master SLave SQL Error $(date +%F)" 1176494252@qq.com < /tmp/sql_err.log echo "邮件通知成功......" } slave_io_error_message(){ mysql -uroot -p123.com -e "show slave status\G"|grep "Last_IO" > /tmp/io_err.log mail -s "MySQL Master SLave IO Error $(date +%F)" 1176494252@qq.com < /tmp/io_err.log echo "邮件通知成功......"} if [ $IO_Status == "Yes" ] && [ $SQL_Status == "Yes" ];then echo "MySQL主从正常" else #1.判断IO异常 if [ ! $IO_Status == "Yes" ];then slave_io_error_message exit fi #2.判断SQL异常 if [ ! $SQL_Status == "Yes" ];then SQL_Err=$(mysql -uroot -p123.com -e "show slave status\G"|awk '/Last_SQL_Errno/ {print $2}') #3.精细化判断主从不同步的问题 case $SQL_Err in 1007) echo "主从的SQL出现问题，尝试使用set global sql_slave_skip_counter=1; 跳过错误" sleep 2 mysql -uroot -p123.com -e "stop slave;set global sql_slave_skip_counter=1;start slave;" SQL_Err_1=$(mysql -uroot -p123.com -e "show slave status\G"|awk '/Last_SQL_Errno/ {print $2}') if [ $SQL_Err_1 -eq 0 ];then echo "尝试跳过了一次，恢复MySQL数据库成功" else slave_sql_error_message fi ;; 1032) slave_sql_error_message ;; *) slav 3. 循环语句while基本概述
while循环语句，只要条件成立就反复执行对应的命令操作，直到命令不成立或为假
01. while循环基础语法
#当条件测试成立（条件测试为真），执行循环体
while 条件测试
do 循环体
done
02. while循环基本使用示例，降序输出10到1的数字
[root@qiudao /scripts]# cat while-1.sh #!/bin/bash var=10 while [ $var -gt 0 ] do echo $var var=$[$var-1]done #简单加法表 [root@qiudao /scripts]# cat while-2.sh #!/usr/bin/bash a=1 b=10 while [ $a -le 10 ] do sum=$(( $a + $b )) echo $a + $b = $sum let a++ let b-- done
03. while循环基本使用示例，输出如下图，两数相乘。
#自增[root@qiudao /scripts]# cat while-3.sh #!/bin/bash num=9 while [ $num -ge 1 ] do sum=$(( $num * $num )) echo "$num * $num = $sum" num=$[$num-1] done \#自减[root@qiudao /scripts]# cat while-4.sh #!/bin/bash num=1 while [ $num -le 9 ] do sum=$(( $num * $num )) echo "$num * $num = $sum" num=$[$num+1] done
4. 循环语句while场景示例
01. 使用while读入文件方式，批量创建用户,while默认按行取值
[root@qiudao /scripts]# cat while-5.sh #!/usr/bin/bash while read line do #1.判断用户是否存在 id $line &>/dev/null if [ $? -eq 0 ];then echo "User: $line already exists" else useradd $line &>/dev/null echo "User: $line Create Ok" fi done<user.txt [root@qiudao /scripts]# cat user.txt ttt1 ttt2 ttt3 ttt4 ttt5 **02.
02. 使用while读入文件方式，批量创建用户以及密码[user:passwd]
使用while读入文件方式，批量创建用户，并赋予一个随机密码**
[root@backup scripts]# cat us.sh #!/bin/bash while read line do user=`echo $line|awk -F: '{print $1}'` pass=`echo $line|awk -F: '{print $2}'` id $user &>/dev/null if [ $? -eq 0 ];then echo "$user已经存在" else useradd $line &>/dev/null && echo $pass |passwd --stdin $user &>/dev/null if [ $? -eq 0 ];then echo "ok" else echo "faile" fi fi done < user.txt 04. while循环场景示例：完成如下猜数字游戏
[root@backup scripts]# cat cai.sh #!/bin/bash ############################################################## # File Name: cai.sh # Time: 2019-10-22-16:51:15 # Author: qls # Organization: www.increase93.com ############################################################## sum=`echo $(( RANDOM % 100 +1 ))` echo "请输入你猜的整数" i=0 while true do read -p "请输入你猜的数字：" int if [[ ! $int =~ ^[0-9]+$ ]];then echo "必须输入整数" continue fi if [ -z $int ];then echo "不能为空" continue fi if [ $int -gt 100 -o $int -lt 0 ];then echo "100以内的数字" continue fi if [ $int -gt $sum ];then echo "猜大了" elif [ $int -lt $sum ];then echo "猜小了" else echo "ok" break fi let a++ done echo "总次数 $(( $a +1 ))"
景示例：随机点菜脚本**
[root@backup scripts]# cat tayn.sh #!/bin/bash main(){ cat <<EOF ##################################### 1.糖醋排骨 30￥ 2.清蒸鲈鱼 50￥ 3.青椒炒蛋 20￥ 4.烤羊排 199￥ 5.结束点菜 ###################################### EOF } >caidan.txt echo "您好！欢迎进入点菜系统" while true do main read -p "请开始点菜：" dian case $dian in 1) echo "糖醋排骨：价格30元" echo "糖醋排骨:30" >>caidan.txt ;; 2) echo "清蒸鲈鱼：价格50元" echo "清蒸鲈鱼:50" >>caidan.txt ;; 3) echo "青椒炒蛋：价格20元" echo "青椒炒蛋:20" >>caidan.txt ;; 4) echo "烤羊排：价格199元" echo "烤羊排:199" >>caidan.txt ;; 5) echo "结束点菜，菜品和价格如下" sort caidan.txt |uniq -c |sort -rn |awk '{print "您点了 "$2"总共"$1""}' awk -F: '{i+=$2}END{print "总价格："i"元"}' caidan.txt exit ;; *) echo "本店无您的需求，抱歉" continue esac done 5. 内置跳出循环语句指令
在我们使用循环语句进行循环的过程中，有时候需要在未达到循环结束条件时强制跳出循环，那么Shell给我们提供了内置方法来实现该功能：exit、break、continue
01. exit，退出整个程序
[root@qiudao /scripts]# cat for-exit.sh #!/bin/bash for i in {1..3} do echo "123" exit echo "456" done echo "done ......" \#执行结果[root@qiudao /scripts]# sh for-exit.sh 123 02. break，结束当前循环，或跳出本层循环
[root@qiudao /scripts]# cat for-break.sh #!/bin/bash for i in {1..3} do echo "123" break echo "456" done echo "done ......" \#执行结果[root@qiudao /scripts]# sh for-break.sh 123 done ...... 
03. continue，忽略本次循环剩余的代码，直接进行下一次循环。
[root@qiudao /scripts]# cat for-continue.sh #!/bin/bash for i in {1..3}do echo "123" continue echo "456" done echo "done ......" \#执行结果[root@qiudao /scripts]# sh for-continue.sh 123 123 123 done ...... 
04. 习题：先扫描内网网段所有主机，存活的则下发当前主机的公钥。
[root@qiudao /scripts]# cat key.sh #!/bin/bash
删除旧的密钥对
rm -f ~/.ssh/id_rsa*
创建密钥对
ssh-keygen -t rsa -f ~/.ssh/id_rsa -N "" &>/dev/null
批量分发公钥的操作
for ip in {2..10} do ping -W1 -c1 172.16.1.$ip &>/dev/null if [ $? -eq 0 ];then #z注意密码根端口 sshpass -p123 ssh-copy-id -p2222 -i ~/.ssh/id_rsa.pub "-o StrictHostKeyChecking=no" 172.16.1.$ip &>/dev/null if [ $? -eq 0 ];then echo -e "\033[32mhost 172.16.1.$ip Distribution of the secret key Success!!! \033[0m" echo else echo -e "\033[31mhost 172.16.1.$ip Distribution of the secret key Failed !!! \033[0m" echo fi else echo -e "\033[31mhost 172.16.1.$ip Destination Host Unreachable! \033[0m" continue fi done