记录 shell学习过程（4）for 循环

1. for in

 for i in `seq  `   #seq 生成从1到10  如果生成从10到1则写作 seq 10 -1 1
   do
      echo $i
 done

for in 也可以循环出字符串

for i in where is a will there is a way
   do
      echo "word:$i"
done

2.双小括号

 for (( i=;i<;i++ )) #2个小括号是为了做运算
   do
       echo $i
 done

3.一个简单的测试主机是否在线的shell

for ((;;))
  do
     ping -c1 $ &>/dev/null
     if [ $? -eq  ]
        then
            echo -e "`date +"%F %H:%M:%S"` : $1 is \033[32m UP \033[0m"
        else
            echo -e "`date +"%F %H:%M:%S"` : $1 is \033[31m Down \033[0m"
        fi

     sleep
done