本节所讲内容
21，1 case - 流程控制语句
21.2 循环循环语句
21.3 循环语句嵌套
21.4 实战-3个shell脚本实战
21.1 流程控制语句
控制语句：
case 变量值 in
变量或者表达式1 ）
命令序列1
；；
变量或者表达式1 ）
命令序列2
；；
.........
*）
默认命令序列
esac
case 语句执行流程控制
例1 编写一个操作文件的脚本
################################################
# File Name : case-1.sh
Author:xuegod
############################################################
#! /bin/bash
cat < ******************** ** 1.backup ** 2.copy ** 3.quit 1)[root@localhost ~]# vim case-1.sh 2)#! /bin/bash ######################################################################################################3 # File Name: case-1.sh # Author: xuegod ######################################################################################################3 cat < ************** ** 1.backup ** ** 2. copy ** ** 3. quit ** ************** eof read -p "Input your choose:" OP case $OP in 1|backup) echo "BACKUP" ;; 2|copy) echo "COPY" ;; 3|quit) exit ;; *) echo error esac 3) [root@localhost ~]# bash case-1.sh ************** ** 1.backup ** ** 2. copy ** ** 3. quit ** ************** 1）[root@localhost ~]# yum -y install httpd 2)[root@localhost ~]# vim case2-.sh 3) #! /bin/bash case $1 in start ) systemctl $1 httpd ps aux | grep httpd echo "httpd start" ;; stop) systemctl $1 httpd ps aux | grep httpd echo "httpd stop" ;; status) systemctl $1 httpd ;; rstart) systemctl $1 httpd echo "httpd restart" ;; *) echo "USAGE: $0 start| stop| restart" esac 4)[root@localhost ~]# systemctl start httpd root 13694 0.4 0.2 224056 5008 ? Ss 20:58 0:00 /usr/sbin/httpd -DFOREGROUND apache 13697 0.0 0.1 226140 3096 ? S 20:58 0:00 /usr/sbin/httpd -DFOREGROUND apache 13698 0.0 0.1 226140 3096 ? S 20:58 0:00 /usr/sbin/httpd -DFOREGROUND apache 13699 0.0 0.1 226140 3096 ? S 20:58 0:00 /usr/sbin/httpd -DFOREGROUND apache 13700 0.0 0.1 226140 3096 ? S 20:58 0:00 /usr/sbin/httpd -DFOREGROUND apache 13701 0.0 0.1 226140 3096 ? S 20:58 0:00 /usr/sbin/httpd -DFOREGROUND root 13717 0.0 0.0 112712 944 pts/1 R+ 20:58 0:00 grep httpd 21.2.1 for-do-done 语法格式 for var in list do commands done 或 for var in list ; do commands done 取值列表有多种取值方式；比如 可以直接读取in 后面的值，默认以空格分隔 例1 1）[root@localhost ~]# vim for-1.sh 2) #! /bin/bash for var in a1 b1 c1 d1 do echo the text is $var done ~ 3) [root@localhost ~]# bash for-1.sh the text is a1 the text is b1 the text is c1 the text is d1 列表中的复杂值，可以使用引号或者转义符 ”/” 来加以约束 1）[root@localhost ~]# vim for-2.sh 2）#! /bin/bash for var in a1 b1 "c1 d1" e2 "hello world" do echo $var done 还要一种的转义符 #! /bin/bash for var in a1 b1\'1 "c1 d1 e2 hello world" I\'s a22 do echo $var done 3）[root@localhost ~]# bash for-2.sh a1 b1 c1 d1 e2 hello world 例子4 1）vim for-4.sh 2) list="a1 b1 c1 d1" for i in $list do echo is a $i done 3) [root@localhost ~]# bash for-4.sh is a a1 is a b1 is a c1 is a d1 cat for-4.sh #! /bin/bash list="a1 b1 c1 d1" for i in $list do echo is a $i done [root@localhost ~]# cat /etc/hosts 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 ①[root@localhost ~]# vim for-5.sh ②#! /bin/bash for i in `cat /etc/hosts` do echo $i done ~ ③ [root@localhost ~]# bash for-5.sh 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 默认情况下，bash shell 会以空格，制表符，换行符作为分隔符，哦通过IFS来自定义分隔符 指定单个字符做分隔符 IFS=: #以： 冒号做分隔符 可以指定多个 如 IFS='\n':;" # 这个赋值会将反斜杠，n,冒号，分号，双引号作为字段分隔符 注：$'\n' 与'\n' 时的区别 IFS='\n' # 将字符\ 和字符n 作为IFS 的换行符 IFS=$'\n' # 真正使用换行符作为分隔符 cat for-6.sh 指定以\n 回车代表作为for语句分隔符 ① vim for-6.sh ②#! /bin/bash IFS=$'\n' for i in `cat /etc/hosts` do echo $i done ③ [root@localhost ~]# bash for-6.sh 127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6 例7 以冒号作为分隔符 改变其中的shell脚本就行 #! /bin/bash IFS=: for i in `cat /etc/hosts` do echo $i done 6 C 语句风格的for 语法格式 for ((i=0;i<10;i++)) do commands done 例1；单个变量。输出1到10 之间的数字 ①[root@localhost ~]# vim for-8.sh ② #! /bin/bash for (( i=1; i<=10;i++)) do echo num is $i done ~ ③[root@localhost ~]# bash for-8.sh num is 1 num is 2 num is 3 num is 4 num is 5 num is 6 num is 7 num is 8 num is 9 例2 ①[root@localhost ~]# vim for-9.sh ② #! /bin/bash for ((a=1,b=9;a<10;a++,b--)) do echo num is $a ------ $b done ③[root@localhost ~]# bash 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 21.3 while 循环语句和循环嵌套 重复测试指令的条件 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 语法格式如下 while 测试命令 do 命令 done 注意： 避免陷入死循环， while true ①[root@localhost ~]# vim for-10.sh ②#! /bin/bash var=10 while [ $var -gt 0 ] do echo $var var=$[ $var-1 ] done ③[root@localhost ~]# bash for-10.sh 10 9 8 7 6 5 4 3 2 1 ①[root@localhost ~]# vim while2.sh ②#! /bin/bash num=1 while [ $num -lt 10 ] do sum=$(( $num * $num )) echo "$num * $num=$sum" ((num++)) # let num++ done ③ [root@localhost ~]# bash while2.sh 1 * 1=1 2 * 2=4 3 * 3=9 4 * 4=16 5 * 5=25 6 * 6=36 7 * 7=49 8 * 8=64 9 * 9=81 自增操作 let var ++ 自减操作 let var -- 九九乘法表 例1 ：批量添加a.txt 文件中的5个用户 1 编写脚本的思路 2 编写脚本会用到哪些命令 useradd passwd chage for 3 把变化的数据变量表示 4 选择合适的流程控制 选择 循环 分支 ①vim a.txt ②mk1 ls1 ab1 df1 ni1 ③[root@localhost ~]# vim for-add.sh ④ #! /bin/bash for name in `cat /root/a.txt` #for name in $(cat /root/a.txt) do id $name &> /dev/null if [ $? -ne 0 ];then useradd $name echo "123456" | passwd --stdin $name &> /dev/null echo "user $name create" else echo "user $name is exits" fi done ⑤[root@localhost ~]# bash for-add.sh user mk1 create user ls1 create user ab1 create user df1 create user ni1 create 例2 打印九九乘法表 注意 外层循环行，内层循环 ①[root@localhost ~]# vim 99.sh ②#! /bin/bash for i in `seq 9` do for j in `seq 9` do [ $j -le $i ] && echo -n "$i*$j= `echo $(($i*$j))`" done echo " " done ③[root@localhost ~]# bash 99.sh 1*1= 1 2*1= 22*2= 4 3*1= 33*2= 63*3= 9 4*1= 44*2= 84*3= 124*4= 16 5*1= 55*2= 105*3= 155*4= 205*5= 25 6*1= 66*2= 126*3= 186*4= 246*5= 306*6= 36 7*1= 77*2= 147*3= 217*4= 287*5= 357*6= 427*7= 49 8*1= 88*2= 168*3= 248*4= 328*5= 408*6= 488*7= 568*8= 64 9*1= 99*2= 189*3= 279*4= 369*5= 459*6= 549*7= 639*8= 729*9= 81 ①vim log .sh ② SRC_DIR=/var/log/ DES_DIR=/opt/backup/`date +%Y%m%d` if [ ! -d $DES_DIR ] ; then mkdir -p $DES_DIR fi for i in `find $SRC_DIR -name "*.log"` do tar czf $i.tgz $i done mv /var/log/*.tgz $DES_DIR ls -lh $DES_DIR echo "The scripts exec end, Files tar successfully !" ③[root@localhost ~]# bash log.sh mkdir: cannot create directory ‘/opt/backup’: Not a directory tar: Removing leading `/' from member names tar: Removing leading `/' from member names tar: Removing leading `/' from member names tar: Removing leading `/' from member names例2 ： 编写一个启动Apache 脚本
5) [root@localhost ~]# bash case2-.sh start
21.2 循环语句
#! /bin/bash从变量中取值
4 从命令中取值
5 自定义shell分隔符
21.3.2 嵌套循环
#!/bin/bash