shell脚本学习总结09--分支与循环结构

if 条件语句

if [[ $ = start  ]];then
    echo start app
elif [[ $ = stop ]];then
    echo stop app
elif [[ $1 = ... ]];then
....
else
   echo Please input command!
fi

 case条件语句

#/bin/bash
    read -p "Please input number: " option
    case  $option in
        "")
        echo "the number you input is 1"
        ;;
        "")
        echo "the number you input is 2"
        ;;
        [-])
        echo "the number you input is $option"
        ;;
        *)
        echo ” the number must less 9"
        ;;
    esac

其中条件部分可以写成 "1|99",[3-9]等

while循环语句

#/bin/bash
   sum=0
   i=0
   while ((i<=10))
   do
     ((sum=sum+i))
     ((i++))
   done
   echo $sum

一般用while做死循环的情况较多

#/bin/bash
   while true
   do
   uptime
   sleep
   done

还有一种用于一行一行的读取输入文件

lsof -i:|awk '{print $2}'|while read line;do [ $line != PID ]&& kill - $line;done

for

#/bin/bash
#   for i in `ls /usr/local/src`
    for i in {sleep,dinner,sport}
    do
    echo $i
    done   

还有一种c语言风格的，

##计算0加到100

#/bin/bash
   sum=
   for ((i=;i<=;i++))
   do
   sum=$(($sum+$i))
   done
   echo $sum