case 判断

• case判断适用的场景，if 都可以使用
• if 单分支情况下 一般使用 case

1，语法

case $ in
条件|条件)                   -------------> 相当于if语句中的 if
    判断
    ;;
条件|条件|条件）                  -------------> 相当于if语句中的 elif
    判断
    ;;
*)                     -------------> 相当于if语句中的 else
    判断
esac                   -------------> 相当于if语句中的 fi

2, 使用

--
     输入喜欢的食物；
     当输入面条，显健康食品；
     输入巧克力，显示发胖食品；
     输入其他的，显示垃圾食品

root@m01~]# vim /script/food.sh
#!/bin/bash
read -p "请输入喜爱的食物：面条 巧克力 辣条：     " food
case $food in
"面条")
    echo "健康食品"
    ;;
"巧克力")
    echo "发胖食品"
    ;;
*)
    echo "垃圾食品"
esac

[root@m01~]# chmod +x /script/food.sh
[root@m01~]# /script/food.sh
请输入喜爱的食物：面条 巧克力 辣条：     面条
健康食品

--- 案例 nginx源码包下载，脚本设置开启关闭命令 ---

1, 源码安装nginx

#官网下载源码包
[root@\ web01~]# wget http://nginx.org/download/nginx-1.18.0.tar.gz
[root@\ web01~]# ll
-rw-r--r--  1 root root 1039530 2020-04-21 22:33 nginx-1.18.0.tar.gz
# 解压
[root@\ web01~]# tar xf nginx-1.18.0.tar.gz


# 到加压包目录下编译，缺少依赖包
[root@\ web01~]# cd nginx-1.18.0/
[root@\ web01~/nginx-1.18.0]# ./configure --prefix=/usr/local/nginx
checking for OS
 + Linux 3.10.0-957.el7.x86_64 x86_64
checking for C compiler ... not found

./configure: error: C compiler cc is not found


# 查看依赖工具包
[root@\ web01~/nginx-1.18.0]# yum -y grouplist
Loaded plugins: fastestmirror
There is no installed groups file.
Maybe run: yum groups mark convert (see man yum)
Loading mirror speeds from cached hostfile
 * base: mirrors.aliyun.com
 * extras: mirrors.aliyun.com
 * updates: mirrors.aliyun.com
Available Environment Groups:
   Minimal Install
   Compute Node
   Infrastructure Server
   File and Print Server
   Cinnamon Desktop
   MATE Desktop
   Basic Web Server
   Virtualization Host
   Server with GUI
   GNOME Desktop
   KDE Plasma Workspaces
   Development and Creative Workstation
Available Groups:
   Cinnamon
   Compatibility Libraries
   Console Internet Tools
   Development Tools
   Educational Software
   Electronic Lab
   Fedora Packager
   General Purpose Desktop
   Graphical Administration Tools
   Haskell
   LXQt Desktop
   Legacy UNIX Compatibility
   MATE
   Milkymist
   Scientific Support
   Security Tools
   Smart Card Support
   System Administration Tools
   System Management
   TurboGears application framework
   Xfce
Done


# 安装依赖工具包
[root@\ web01~/nginx-1.18.0]# yum -y groupinstall "Development Tools"

[root@\ web01~/nginx-1.18.0]# ./configure --prefix=/usr/local/nginx

... ..../configure: error: the HTTP gzip module requires the zlib library.
You can either disable the module by using --without-http_gzip_module
option, or install the zlib library into the system, or build the zlib library
statically from the source with nginx by using --with-zlib=<path> option.


#根据提示继续下载依赖包
[root@\ web01~/nginx-1.18.0]# yum install -y zlib*

再次执行
[root@\ web01~/nginx-1.18.0]# ./configure --prefix=/usr/local/nginx

[root@\ web01~/nginx-1.18.0]# make && make install

• 源码安装nginx 开启或关闭nginx使用命令/usr/local/nginx/sbin/nginx -s stop 等较麻烦

2, 脚本编写

[root@\ web01~]# vim /script/nginx.sh
#!/bin/bash
[ $# -ne 1 ] && echo "Usage: $0 {start|stop|restart|reload|status}" && exit
case $1 in
"start")
    echo "nginx is ready to start"
    /usr/local/nginx/sbin/nginx &> /dev/null
    ps -ef | grep [n]ginx | grep master &> /dev/null
    if [ $? -eq 0 ];then
        echo "nginx has benn started"
    else
        /user/local/nginx/sbin/nginx &> /dev/null
        if [ $? -eq 0 ];then
            echo "nginx start succeed"
        else
           echo "failed to start nginx"
        fi
    fi
    ;;
"stop")
    echo "nginx is ready to stop"
    /usr/local/nginx/sbin/nginx -s stop
    if [ $? -eq 0 ];then
        echo "nginx has been stopped"
    else
        echo "failed to stop nginx"
    fi
    ;;
"restart")
    /usr/local/nginx/sbin/nginx -s stop
    if [ $? -eq 0 ];then
        echo "nginx has been stopped"
    else
        echo "faild to stop nginx"
        /usr/local/nginx/sbin/nginx -s stop
        if [$? -ne 0 ];then
            echo "nginx has been started"
        else
            echo "failed to stop nginx"
        fi
    fi
    ;;

"status")
    ps -ef | grep [n]ginx | grep master &> /dev/null
    if [ $? -eq 0 ];then
        echo "nginx is up"
    else
        echo "nginx is down"
    fi
    ;;
    esac

3,验证

[root@\ web01~]# chmod +x /script/nginx.sh

[root@\ web01~]# /script/nginx.sh status
nginx is down

[root@\ web01~]# /script/nginx.sh start
nginx is ready to start
nginx has benn started

[root@\ web01~]# /script/nginx.sh stop
nginx is ready to stop
nginx has been stopped

[root@\ web01~]# /script/nginx.sh restart
nginx has been stopped
succeed to start nginx

4,优化脚本

[root@\ web01~]# vim /script/nginx.sh
!/bin/bash
[ $# -ne 1 ] && echo "Usage: $0 {start|stop|restart|status}" && exit
function start_nginx(){
    ps -ef | grep [n]ginx | grep master &> /dev/null
    if [ $? -eq 0 ];then
        echo "nginx has benn started"
    else
        /usr/local/nginx/sbin/nginx &> /dev/null
        if [ $? -eq 0 ];then
            echo "nginx start succeed"
        else
           echo "failed to start nginx"
        fi
    fi
}
function stop_nginx(){
    ps -ef | grep [n]ginx | grep master &> /dev/null
    if [ $? -ne 0 ];then
        echo "nginx has been stopped"
    else
        /usr/local/nginx/sbin/nginx -s stop &> /dev/null
        ps -ef | grep [n]ginx | grep master &> /dev/null
        if [ $? -ne 0 ];then
            echo "succeed to stop nginx"
        else
            echo "failed to stop nginx"
        fi
    fi
}

case $1 in
"start")
    start_nginx
    ;;
"stop")
    stop_nginx
    ;;
"restart")
    stop_nginx
    start_nginx
    ;;

"status")
    ps -ef | grep [n]ginx | grep master &> /dev/null
    if [ $? -eq 0 ];then
        echo "nginx is up"
    else
        echo "nginx is down"
    fi
    ;;
    esac



##注意：用函数function（下几篇会单独讲到）方便调用
       nginx_stop环节加一行sleep 1代码；
       该命令执行需要时间，如果nginx是开启状态，执行 /usr/local/nginx/sbin/nginx -s stop，  立刻执行开启nginx，很有可能$?是0，但是其实没有重启，是本身就开启的状态