Shell(4) Conditional Control Statement

一. while循环

当前条件表达式成立(为真)则执行do后面的命令

语法结构:
while [ 条件表达式 ]
do
     命令的集合
done 

案例: 写一个死循环脚本

第一种

[[email protected] ]# cat while.sh 
while true
do
	  echo test
	  sleep 2
done

第二种

[[email protected] day3]# cat while.sh 
while [ 10 -gt 5 ]
do
	  echo test
	  sleep 2
done

第三种

[[email protected] day3]# cat while.sh
while [ -f /etc/hosts ]
do
	  echo test
	  sleep 2
done

while数字循环

[[email protected] ]# cat while.sh
i=1
while [ $i -le 10 ]
do
	  echo $i
	  let i++
done
[[email protected] ]# sh while.sh
1
2
3
4
5
6
7
8
9
10

案例: while从1加到100

[[email protected] ]# cat while.sh
i=1
while [ $i-le100]docount=$[count+i]
let i++
done
echo $count
[[email protected] ]# sh while.sh
5050

案例: while读取文件

forThe loop reads the file separated by spaces whileLoops are separated by lines

[[email protected] ]# cat read.sh
#!/bin/bash
while read line
do
	 echo $line
done</etc/hosts
[[email protected] ]# sh read.sh
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain localhost6 localhost6.localdomain6

案例: while创建用户

使用for循环(command line execution)

[[email protected] ]# for i in 取值列表; do 执行的命令;done
[[email protected] ]# for i in `cat user.txt`;do echo $i;done
aa
qq
bb
cc

[[email protected] ]# for i in `cat user.txt`;do useradd $i;done
[[email protected] ]# tail -4 /etc/passwd
aa:x:1000:1000::/home/aa:/bin/bash
qq:x:1001:1001::/home/qq:/bin/bash
bb:x:1002:1002::/home/bb:/bin/bash
cc:x:1003:1003::/home/cc:/bin/bash

forLoop delete users

[[email protected] ]# for i in `cat user.txt`;do userdel -r $i;done

使用while循环批量创建用户

[[email protected] ]# cat user.sh
#!/bin/bash
while read line
do
	  useradd $line
done< user.txt
[[email protected] ]# sh user.sh
[[email protected] ]# tail -4 /etc/passwd
aa:x:1000:1000::/home/aa:/bin/bash
qq:x:1001:1001::/home/qq:/bin/bash
bb:x:1002:1002::/home/bb:/bin/bash
cc:x:1003:1003::/home/cc:/bin/bash

Create users in batches by passing user parameters

[[email protected] ]# cat user.sh
#!/bin/bash
read -p "Please enter the user's prefix name: " pre 
read -p "Please enter the number of users to create: " num
i=1
while [ $i -le $num ] 
do
      user=${pre}$i
      id $user &>/dev/null
	  re=$?
      if [ $re -ne 0 ];then
         useradd $user
         [ $? -eq 0 ] && echo "$user 创建成功"
	  elif [ $re -eq 0 ]
	     echo "$user 已经存在"
      fi  
      let i++
done

while多级跳

三层循环:

[[email protected] ]# cat while1.sh 
#!/bin/bash
while true
do
         echo "第一级"
         sleep 1
         while true
	 do
	     echo "第二级"
	     sleep 1

	     while true
	     do
	       echo "第三级"
	       sleep 1
	     done

	 done
done
echo done....................

break跳出循环

[[email protected] ]# cat while1.sh 
#!/bin/bash
while true
do
         echo "第一级"
         sleep 1
         while true
	 do
	     echo "第二级"
	     sleep 1

	     while true
	     do
	       echo "第三级"
	       sleep 1
	       break 3
	     done

	 done
done
echo done....................

exit 退出整个脚本

continue Execution continues from the beginning, ignoring the rest of the code

[[email protected] ]# cat while1.sh 
#!/bin/bash
while true
do
		 echo "第一级"
		 sleep 1
		 while true
	 do
		 echo "第二级"
		 sleep 1
		 continue
		 while true
		 do
		   echo "第三级"
		   sleep 1
		 done

	 done
done
echo done....................

break Exit the loop and continue execution

[[email protected] ]# cat user.sh
#!/bin/bash
read -p "Please enter the user's prefix name: " pre 
read -p "Please enter the number of users to create: " num
i=1
while [ $i -le $num ] 
do
	  user=${pre}$i
	  id $user &>/dev/null
	  if [ $? -ne 0 ];then
		 useradd $user
		 [ $? -eq 0 ] && echo "$user 创建成功"
	  else
	 break
	  fi  
	  let i++
done
echo done..............

continue:

[[email protected] ]# cat user.sh 
#!/bin/bash
read -p "Please enter the user's prefix name: " pre 
read -p "Please enter the number of users to create: " num
i=0
while [ $i -le $num ] 
do
	  let i++
	  user=${pre}$i
	  id $user &>/dev/null
	  if [ $? -ne 0 ];then
		 useradd $user
		 [ $? -eq 0 ] && echo "$user 创建成功"
	  else
	      continue
	  fi  
done
echo done..............

---

#!/bin/bash
>test.txt
while true
do
	  ran=`echo $((RANDOM%100+1))`
	  if [ `grep -w $ran test.txt|wc -l` -eq 1 ];then
		 continue
	  fi
	  echo $ran >> test.txt
done

---

二.函数

函数的特点:

1. 先定义在调用 If it is only defined and not called, the script will not execute(Variables are only defined but not called and assignments are performed)
2. Functions are commands(代码)的集合(变量只能赋一个值 Functions can be assigned multiple values)
3. 可以重复调用

Variable to call the script

[[email protected] ]# cat 1.sh 
name=oldboy
[[email protected] ]# cat 2.sh 
. /server/scripts//1.sh
read -p "请输入你的年龄: " num
echo 名字: $name 年龄: $num

1.函数的定义

[[email protected] ]# cat fun.sh 
#!/bin/bash
fun1(){
    
     echo "第一种书写方式"
}
function fun2 {
    
     echo "第二种书写方式"
}
function fun3(){
    
     echo "第三种书写方式"
}
fun1			# 调用函数 Write the function name directly below the function to call
fun2
fun3

函数复用:

[[email protected] ]# source fun.sh 
第一种书写方式
第二种书写方式
第三种书写方式
[[email protected] ]# fun1
第一种书写方式
[[email protected] ]# fun2
第二种书写方式
[[email protected] ]# fun3
第三种书写方式

2.函数的传参

Functions cannot directly receive arguments from scripts
You need to use the parameter passing method of the function to pass parameters
Pass parameters directly after the calling function

[[email protected] ]# cat fun.sh
#!/bin/bash
fun(){
    
	 if [ -f $1 ]
	 then
	 echo "$1 文件存在"
	 else
	 echo "$1 文件不存在"
	 fi
}
fun /etc/hosts /etc/passwd		# Pass parameters directly after the calling function name

[[email protected] ]# sh fun.sh
/etc/hosts 文件存在
[[email protected] ]# sh -x fun.sh 
+ fun /etc/hosts /etc/passwd
+ '[' -f /etc/hosts ']'
+ echo '/etc/hosts 文件存在'
/etc/hosts 文件存在


[[email protected] ]# cat fun.sh
#!/bin/bash
fun(){
    
	 if [ -f $2 ]
	 then
	 echo "$2 文件存在"
	 else
	 echo "$2 文件不存在"
	 fi
}
fun $2 $1
[[email protected] ]# sh fun.sh /etc/hosts /etc/passwd
/etc/hosts 文件存在

3.函数的变量

The current global variable is supported in the function

[[email protected] ]# cat fun.sh 
#!/bin/bash
file=/etc/hosts
fun(){
    
	 if [ -f $file ]
	 then
	 echo "$file 文件存在"
	 else
	 echo "$file 文件不存在"
	 fi
}
fun


[[email protected] ]# cat fun.sh 
#!/bin/bash
num=2
fun(){
    
	 for i in `seq $num`
	 do
	 count=$[$count+$num]
	 done 
	 echo $count
}
fun

Define the local variables of the function: Only takes effect within the function body

[[email protected] ]# cat fun.sh 
#!/bin/bash
fun(){
    
	 local num=20
	 for i in `seq $num`
	 do
	 count=$[$1+$num]
	 done 
	 echo $count
}
fun 10
echo $num

4.函数的返回值

通过exit返回状态码:

[[email protected] day2]# cat env.sh 
#!/bin/sh
read -p "Please Input name env: " name
[ -z $name ] && echo "A name is required" && exit
if [[  $name =~ ^[a-Z]+$ ]];then
   echo $name
else
   exit 100
fi


read -p "Please Input age env: " age
if [[ $age =~ ^[0-9]{
    2}$ ]];then
  echo $age
else
   exit 200
fi
echo $name $age

by assignment:

[[email protected] ]# cat fun.sh
#!/bin/bash
fun(){
    
	 if [ -f $1 ]
	 then
		 return 50
	 else
		 return 100
	 fi
}
fun $1
re=$?
if [ $re -eq 50 ]
then
	 echo "$1 文件存在"
elif  [ $re -eq 100 ]
then
	 echo "$1 文件不存在"
fi
[[email protected] ]# sh fun.sh /etc/passwd
/etc/passwd 文件存在
[[email protected] ]# sh fun.sh /etc/passwdssss
/etc/passwdssss 文件不存在

案例: 重复判断

# 判断下载YUMA function of whether the warehouse is successful
test_yum(){
    
    if [ $re -eq 0 ];then
    action "yum仓库安装" /bin/true
    else
    action "yum仓库安装" /bin/false
    fi
}

if [ ${os_vs%%.*} -eq 7 ]
then
    # 备份默认YUM仓库
    $backup_yum
    # 下载新的YUM仓库
    wget -O /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo &>/dev/null
	#将执行的返回结果赋值给re
    re=$?
	#Call the function name to execute the command in the function body
    test_yum

elif [ ${os_vs%%.*} -eq 6 ]

案例: 显示主菜单

[[email protected] ]# cat menu.sh 
#!/bin/bash
menu1(){
    
       echo "1.PHP"
   	   echo "2.MySQL"
   	   echo "h.显示主菜单"
}
menu1
while true
do
	   read -p "Please enter the service tag you want to install: " num
           if [ $num = 1 ];then
              while true
	      do
	          echo "1.PHP1.1"
	          echo "2.PHP1.2"
	          echo "3.返回主菜单"
	          read -p "Please enter the installed version number: " re
  		  if [ $re -eq 1  ];then
	   	     echo yum php1.1.....
		  elif [ $re -eq 3 ];then
	 	      break
		  fi
 	      done
 	   elif [ $num = 2 ];then
	      echo "1.MySQL1.1"
	      echo "2.MySQL1.2"
	   elif [ $num = h  ];then
 	      menu1
  	   fi
done

三. case

语法结构:
变量: 直接取值 read读入 赋值
case 变量 in
		  匹配模式1)
			  命令集合
		  ;;
		  匹配模式2)
			  命令集合
		  ;;
		  匹配模式3)
			  命令集合
		  ;;
		  *)
			  None of the above patterns were matched 则执行 * 下的命令
esac

案例:创建或删除用户

[[email protected] ]# cat case.sh 
#!/bin/bash
for i in `seq 10`
do
   echo oldboy$i
done
read -p "Choose to delete or create the above user:[y创建|d删除] " num

case $num in
	y)
	    for a in `seq 10`
	    do
	           user=oldboy$a
	           id $user &>/dev/null
		   if [ $? -eq 0 ];then
	 	      echo $user 用户存在
		   else
		      useradd $user
		      [ $? -eq 0 ] && echo $user 创建成功
		   fi

	    done
	;;
	d)
	    for a in `seq 10`
            do
                   user=oldboy$a
                   id $user &>/dev/null
                   if [ $? -eq 0 ];then
                      userdel -r $user
		      [ $? -eq 0 ] && echo $user 删除成功
                   else
                      echo "$user 用户不存在"
                   fi

            done

        ;;
        *)
	     echo "Usage: $0 [y|yes|d|del]"
esac

---

for循环包含case语句

[[email protected] ]# cat case.sh 
#!/bin/bash
for i in `seq 10`
do
   echo oldboy$i
done

read -p "Choose to delete or create the above user:[y创建|d删除] " num

for a in `seq 10`
do
	case $num in
		y)
		  user=oldboy$a
		  id $user &>/dev/null
		   if [ $? -eq 0 ];then
		      echo $user 用户存在
		   else
		      useradd $user
		      [ $? -eq 0 ] && echo $user 创建成功
		   fi

		;;
		d)
			   user=oldboy$a
			   id $user &>/dev/null
			   if [ $? -eq 0 ];then
			      userdel -r $user
			      [ $? -eq 0 ] && echo $user 删除成功
			   else
			      echo "$user 用户不存在"
			   fi

		;;
		*)
		     echo "Usage: $0 [y|yes|d|del]"
	esac
done

---

案例: 查看系统信息

菜单:

1. 显示登录信息(执行w)
2. 显示内存
3. 显示磁盘
4. 显示IP地址
5. show extranetIP地址
6. 显示主机名称
7. 显示菜单(You can clear the screen first in the display menu)

通过case语句执行 写入死循环

[[email protected] ]# cat os.sh 
#!/bin/bash
menu(){
    
	echo -e "\t\t\t\t\t\t1.f查看内存"
	echo -e "\t\t\t\t\t\t2.d查看磁盘"
	echo -e "\t\t\t\t\t\t3.u查看负载"
	echo -e "\t\t\t\t\t\t4.l查看登录信息"
	echo -e "\t\t\t\t\t\t5.c查看外网IP地址"
	echo -e "\t\t\t\t\t\t6.m显示菜单"
	echo -e "\t\t\t\t\t\t7.q退出脚本"
}
menu
while true
do
	read -p "Please enter the system information number to view[1|f]: " num
	case $num in
		  1|f)
		   free -h
		  ;;
		  2|d)
		   df -h
		 ;;
		  3|u)
		   uptime
		  ;;
		  4|l)
		   w
		 ;;
		  5|c)
		   curl cip.cc
		  ;;
		 6|m)
		    clear
		    menu
		  ;;
		 7|q)
	  	    exit
		  ;;
		  *)
		   echo "Usage: $0 [1|2|3|4|5|6]"
	esac
done

案例: Nginx启动脚本

启动 /usr/sbin/nginx
停止 /usr/sbin/nginx -s stop
重启 Stop first and then start /usr/sbin/nginx -s stop && /usr/sbin/nginx
重载 /usr/sbin/nginx -s reload
状态 自定义

[[email protected] ]# cat nginx.sh 
#!/bin/bash
. /etc/init.d/functions
re=$1
fun(){
    
              if [ $? -eq 0 ];then
              action "Nginx $re is " /bin/true
              else
              action "Nginx $re is " /bin/false
              fi
}
case $1 in
	 start)
	      /usr/sbin/nginx
 	      fun
	 ;;
	 stop)
	      /usr/sbin/nginx -s stop
 	      fun
	 ;;
	 restart)
	      /usr/sbin/nginx -s stop
	      sleep 1
	      /usr/sbin/nginx
 	      fun
 	 ;;
	 reload)
	      /usr/sbin/nginx -s reload
 	      fun
	 ;;
	 status)
	      num=`ps axu|grep nginx|grep master|wc -l`
  	      if [ $num -eq 1 ];then
	         action "Nginx is running...."   /bin/true
	      else
	         action "Nginx is down......."   /bin/false
	      fi
 	 ;;
	 *)
	  echo "Usage: $0 [start|stop|restart|reload|status]"
esac