第八章 流程控制之case语句

1 语法

  1. case 变量 in
  2. 模式1)
  3.     代码1
  4.     ;;
  5. 模式2)
  6.     代码2
  7.     ;;
  8. 模式3)
  9.     代码3
  10.     ;;
  11. *)
  12.     无匹配后命令序列
  13. esac

2 案例

2.1 案例1 猜数字

  1. [root@xujun1270 ~]# cat case-1.sh 
  2. #!/bin/bash
  3. read -p "qing shu ru shu zi:" num
  4. case "$num" in 
  5.     1)
  6.      echo "zhe ge shu zi shi 1"
  7.      ;;
  8.     2)
  9.      echo "zhe ge shu zi shi 2"
  10.      ;;
  11.     3)
  12.      echo "zhe ge shu zi shi 3"
  13.      ;;
  14.    *)
  15.      echo "bi xu you shu zi"
  16.      exit 2
  17. esac

2.2 案例2 根据水果的不同，打印出对应的颜色

  1. [root@xujun1270 ~]# cat case-2.sh
  2. #!/bin/bash
  3. RED_COLOR='\E[1;31m'
  4. GREEN_COLOR='\E[1;32m'
  5. YELLOW_COLOR='\E[1;33m'
  6. BLUE_COLOR='\E[1;34m'
  7. RES='\E[0m'
  8. menu(){
  9. cat <<EOF
  10. ==================
  11. 1.apple
  12. 2.pear
  13. 3.banana
  14. 4.cherry
  15. =================
  16. EOF
  17. }
  18. menu
  19. read -p "pls select color:" num
  21. case $num in
  22.    1)
  23.      echo -e "${RED_COLOR}apple${RES}"
  24.      ;;
  25.    2)
  26.      echo -e "${GREEN_COLOR}pear${RES}"
  27.      ;;
  28.    3)
  29.      echo -e  "${YELLOW_COLOR}banana${RES}"
  30.      ;;
  31.    4)
  32.      echo -e  "${BLUE_COLOR}cherry${RES}"
  33.      ;;
  34.    *)
  35.      echo "$0 be {1|2|3|4}"
  36. esac

2.3 案例3 nginx启动脚本

  1. [root@xujun1270 init.d]# cat nginx.sh
  2. #!/bin/bash
  3. #chkconfig: 2345 40 80
  4. #description：starts，stop and saves iptables firewall
  5. . /etc/init.d/functions
  6. pidfile=/application/nginx/logs/nginx.pid
  7. start_nginx (){
  8.   if [ -f $pidfile ];then
  9.     echo "nginx is running"
  10.   else
  11.     /application/nginx/sbin/nginx &>/dev/null
  12.     action "nginx is started" /bin/true
  13.   fi
  14. }  
  16. stop_nginx (){
  17.   if [  -f $pidfile ];then
  18.     /application/nginx/sbin/nginx -s stop &>/dev/null
  19.     action "nginx is stopped" /bin/true
  20.   else 
  21.     action "nginx is stopped" /bin/false
  22.   fi
  23. }  
  25. reload_nginx (){
  26.    if [  -f $pidfile ];then
  27.     /application/nginx/sbin/nginx -s reload &>/dev/null
  28.     action "nginx is reloaded" /bin/true
  29.   else 
  30.     echo "cat't open $pidfile,no such file or directory"
  31.    fi
  32. }
  34. case $1 in 
  35.      start)
  36.           start_nginx
  37.           RETVAL=$?
  38.           ;;
  39.      stop)
  40.           stop_nginx
  41.           RETVAL=$?
  42.           ;;
  43.      restart)
  44.           stop_nginx
  45.           sleep 3
  46.           start_nginx
  47.           RETVAL=$?
  48.           ;;
  49.       reload)
  50.           reload_nginx
  51.           RETVAL=$?
  52.           ;;
  53.       *)
  54.         echo "$0 {start|stop|restart}"
  55.         exit 1
  56. esac
  57. exit $RETVAL

3 case语句小结

1、case语句就相当于多分支的if语句，但是case语句优势更规范、易读

2、case语句适合变量的值少，且为固定的数字或字符串集合

3、系统服务启动脚本一般都是用case语句