while CONDITION ；do

        statement

        .....

done

进入循环：条件满足

退出循环：条件不满足

until CONDITION；do

        STATEMENT

        .......

done

进入循环：条件不满足

退出循环：条件满足

#！/bin/bash

#

read -p"Input something:" STRING

while [ $STRING!=‘quit‘ ];do

     echo $STRING |tr ‘a-z‘ ‘A-Z‘

    read -p "Again,Input something:"STRING

done

#! /bin/bash

#

read -p "Input something:" STRING

until [ $STRING==‘quit‘ ];do

    echo $STRING |tr ‘a-z‘ ‘A-Z‘

    read -p "Input something:"STRING

done

#! /bin/bash

#

who  | grep"hadoop"&> /dev/null

RETVAL=$?

until [ $RETVAL -eq 0 ];do

    echo"hadoop is not come!"

    sleep 5

    who |grep"hadoop" &> /dev/null

    RETVAL=$?

done

echo"hadoop is logged in"

for 变量 in 列表；do

    循环体

done

for （（expr1；expr2；expr3））；do

    循环体

done

#！/bin/bash

#

declare -i SUM=0

for I in {1...100};do

    let SUM+=$I

done

echo $SUM

declare -i SUM2=0

for((I=1;I<=100;I++));do

    let SUM2+=$I

done

echo $SUM2

ping

    -c

    -w

awk ‘PATTERN{ACTION}‘file

    print $1

awk -F ‘{print $1,$3}‘ /etc/passwd

马哥10-5