shell编程while

脚本编程：
   顺序结构
   选择结构
       if
       case
   循环结构
       for
       while
       until

while循环：适用于循环次数未知的场景，要有退出条件
语法：
   while CONDITION; do
      statement
      ...
   done

计算100以内所有正整数的和

#!/bin/bash
declare -i I=1
declare -i SUM=0

while [ $I -le 100 ]; do
let SUM+=$I
let I++
done

echo $SUM

练习：转换用户输入的字符为大写，除了quit:
#!/bin/bash
#
read -p "Input something: " STRING

while [ $STRING != 'quit' ]; do
echo $STRING | tr 'a-z' 'A-Z'
read -p "Input something: " STRING
done

练习：每隔5秒查看hadoop用户是否登录，如果登录，显示其登录并退出；否则，显示当前时间，并说明hadoop尚未登录：
#!/bin/bash
#
who | grep "hadoop" &> /dev/null
RETVAL=$?

while [ $RETVAL -ne 0 ]; do
echo "`date`, hadoop is not log."
sleep 5
who | grep "hadoop" &> /dev/null
RETVAL=$?
done

echo "hadoop is logged in."

read -p "Your choice: " CHOICE
while [ $CHOICE != 'quit' ];do
case $CHOICE in
d|D)
    echo "Disk usage: "
    df -Ph ;;
m|M)
    echo "Memory usage: "
    free -m | grep "Mem" ;;
s|S)
    echo "Swap usage: "
    free -m | grep "Swap" ;;
*)
    echo "Unknown.." ;;
esac

read -p "Again, your choice: " CHOICE
done

练习：写一个脚本
从键盘让用户输入几个文件，脚本能够将此几个文件归档压缩成一个文件；
read:
-p “PROMPT": 给出提示

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shell编程while

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