【shell】shell if条件判断

我不是女神ヾ 2023-07-03 12:27 23阅读 0赞

# shell if条件判断 #

## 1.if测试格式 ##

分单分支，双分支和多分支，和一般if测试格式相同

单分支        双分支           多分支
    if 条件测试     if 条件测试     if 条件测试
       命令序列     then 命令序列   then 命令序列
    fi             else 命令序列   elif 条件测试1
                   fi             then 命令序列
                                  ...
                                  else 命令序列
                                  fi

实例如下

### 1.1 安装http脚本 ###

[klaus@localhost chapt4]$ cat httpd_yum.sh
    #!/bin/bash
    read -p "Are you sure to install?[y]:" action
    
    if [ ! "${action}" = "y" ];then
       echo -e "Incorrect input!"
       exit
    fi
    
    getway=`ip route | grep 'default via'| awk '{print $3}'`
    ping -c1 www.baidu.com &>/dev/null
    if [ $? -eq 0 ];then
       sudo yum install httpd httpd-devel httpd-manual httpd-tools -y &>/dev/null
       sudo service httpd start &>/dev/null
       sudo service enable httpd &>/dev/null
       sudo sed -ri '/^#ServerName www.example.com:80=/cServerName www.example.com:80' /etc/httpd/conf/httpd.conf
       sudo sed -ri '/^SELINUX=/cSELINUX=disable' /etc/selinux/config
       curl http://127.0.0.1 &>/dev/null
       if [ $? -eq 0 ];then
           echo "Apache is successfully installed"
       fi
    elif ping -c1 $getway &>/dev/null;then
       echo "Check if DNS is correct..."
    else
       echo "Check if ip address is correct..."
    fi
    
    [klaus@localhost chapt4]$ ./httpd_yum.sh
    Are you sure to install?[y]:y
    [sudo] password for klaus:
    Apache is successfully installed

### 1.2 根据自己系统版本更换阿里云镜像 ###

我们可以根据阿里提供的镜像源来获取源地址，具体脚本如下

[klaus@localhost chapt4]$ cat ali_mirrors.sh
    #!/bin/bash
    
    os_version=`cat /etc/redhat-release|awk '{print $3}'|awk -F "." '{print $1}'`
    mv /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.backup
    
    if [ "$os_version" = "6" ];then
       wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
       if [ ! $? -eq 0 ];then
           curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-6.repo
           if [ $? -eq 0 ];then
               echo "Alibaba Cloud mirror replacement is complete!"
               exit
           else
               echo "Program running error, network unreachable!"
               exit
           fi
           echo "Alibaba Cloud mirror replacement is complete!"
       fi
    elif [ "$os_version" = "7" ];then
       wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
       if [ ! $? -eq 0  ];then
           curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo
           if [ $? -eq 0  ];then
               echo "Alibaba Cloud mirror replacement is complete!"
               exit
           else
                echo "Program running error, network unreachable!"
                exit
           fi
           echo "Alibaba Cloud mirror replacement is complete!"
       fi
    elif [ "$os_version" = "8"  ];then
       wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-8.repo
       if [ ! $? -eq 0  ];then
           curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-8.repo
           if [ $? -eq 0  ];then
               echo "Alibaba Cloud mirror replacement is complete!"
               exit
           else
                echo "Program running error, network unreachable!"
                exit
           fi
           echo "Alibaba Cloud mirror replacement is complete!"
       fi
    else
       sudo sed -i -e '/mirrors.cloud.aliyuncs.com/d' -e '/mirrors.aliyuncs.com/d' /etc/yum.repos.d/CentOS-Base.repo
    fi
    [klaus@localhost chapt4]$ sudo ./ali_mirrors.sh
    --2020-02-04 08:15:48--  http://mirrors.aliyun.com/repo/Centos-6.repo
    Resolving mirrors.aliyun.com... 119.36.51.231, 119.36.51.115, 103.98.81.102, ...
    Connecting to mirrors.aliyun.com|119.36.51.231|:80... connected.
    HTTP request sent, awaiting response... 200 OK
    Length: 2523 (2.5K) [application/octet-stream]
    Saving to: “/etc/yum.repos.d/CentOS-Base.repo”
    
    100%[============================================================>] 2,523       --.-K/s   in 0s     
    
    2020-02-04 08:15:48 (229 MB/s) - “/etc/yum.repos.d/CentOS-Base.repo” saved [2523/2523]
    
    [klaus@localhost chapt4]$ ls /etc/yum.repos.d/
    CentOS-Base.repo         CentOS-Debuginfo.repo  CentOS-Media.repo  epel.repo
    CentOS-Base.repo.backup  CentOS-fasttrack.repo  CentOS-Vault.repo  epel-testing.repo

## 2.for循环 ##

循环次数固定，循环格式

for 变量名 [in 取值列表]
    do
        循环体
    done

实例

### 2.1 批量ping主机地址 ###

[klaus@localhost chapt4]$ ls
    ali_mirrors.sh  httpd_yum.sh  ping_batch.sh
    [klaus@localhost chapt4]$ cat ping_batch.sh
    #!/bin/bash
    for i in { 2..245}
    do
        { 
            ip=192.168.84.$i
            ping -c1 -W1 $ip &>/dev/null
            if [ $? -eq 0 ];then
                if [ ! -f ip.txt ];then
                    touch ip.txt
                fi
                echo "$ip" | tee -a ip.txt
            fi
        }&
    done
    wait
    
    echo "finished..."
    [klaus@localhost chapt4]$ ./ping_batch.sh
    192.168.84.2
    192.168.84.129
    finished...

### 2.2 批量创建用户并设置密码 ###

具体的，将用户和密码同时写入一个txt文件中，按照username password的格式

[klaus@localhost chapt4]$ cat user.txt
    tmpuser1 123
    tmpuser2 456
    tmpuser3 789
    
    tmpuser4 000
    [klaus@localhost chapt4]$ cat user
    useradd_for.sh  user.txt        
    [klaus@localhost chapt4]$ cat useradd_for.sh
    #!/bin/bash
    if [ $# -eq 0 ];then
        echo "usage: `basename $0` file!"
        exit 1
    fi
    
    if [ ! -f $1 ];then
        echo "error file!"
        exit 2
    fi
    
    IFS=$'\n' #转义字符
    
    for line in `cat $1`
    do
        username=`echo "$line" | awk '{print $1}'`
        password=`echo "$line" | awk '{print $2}'`
        
        id $username &>/dev/null
        if [ $? -eq 0 ];then
            echo "user $username" already exists!
        else
            sudo useradd $username
            echo "$password" | passwd --stdin $username &>/dev/null
            if [ $? -eq 0 ];then
                echo "$user is created!"
            fi
        fi
    done
    [klaus@localhost chapt4]$ chmod a+x useradd_for.sh
    [klaus@localhost chapt4]$ ./useradd_for.sh user.txt
    [sudo] password for klaus:
    [klaus@localhost chapt4]$ awk -F':' '{ print $1}' /etc/passwd
    root
    bin
    ...
    klaus
    win
    tmpuser1
    tmpuser2
    tmpuser3
    tmpuser4

## 3.while循环 ##

while循环格式

while 条件测试
    do
        循环体
    done

while循环，当条件测试成立时，执行循环体

### 3.1 实例，批量创建用户并设置密码 ###

[klaus@localhost chapt4]$ cat while_useradd.sh
    #!/bin/bash
    if [ $# -eq 0 ];then
        echo "usage: `basename $0` file!"
        exit 1
    fi
    
    if [ ! -f $1 ];then
        echo "error file!"
        exit 2
    fi
    
    #IFS=$'\n'
    
    while read line
    do
    { 
        if [ ${#line} -eq 0 ];then
            continue
        else
            user=`echo "$line" | awk '{print $1}'`
            passwd=`echo "$line" | awk '{print $2}'`
            
            id $user &>/dev/null
            if [ $? -eq 0 ];then
                echo "user $user" already exists!
            else
                sudo useradd $user
                echo "$passwd" | passwd --stdin $user &>/dev/null
                if [ $? -eq 0 ];then
                    echo "$user is created!"
                fi
            fi
        fi
    }
    done < $1
    [klaus@localhost chapt4]$ ./while_useradd.sh nameuser.txt
    [klaus@localhost chapt4]$ awk -F':' '{ print $1}' /etc/passwd
    ...
    klaus
    win
    tmpuser1
    tmpuser2
    tmpuser3
    tmpuser

## 4.until循环 ##

until循环格式

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

### 4.1 网络测试，如果ping不通，延时1s再ping ###

[klaus@localhost chapt4]$ cat until_ping.sh
    #!/bin/bash
    ip=4.2.2.2
    
    until ping -c1 W1 $ip &>/dev/null
    do
        echo "Network is down, try again after 1s delay..."
        sleep 1
    done
    [klaus@localhost chapt4]$ ./until_ping.sh
    Network is down, try again after 1s delay...