Shell While 命令

while循环用于重复地执行一个命令列表

while [ CONDITION ]
do
  command1
  command2
  ...
  ...
  commandN
done

当条件为真时，command1...commandN将被执行。比如，逐行地读取一个文件的内容，

while IFS= read -r line
do
  command1 on $line
  command2 on $line
  ...
  commandN
done < "/path/to/file:

定义一个无限while循环可以使用如下三种命令
true不做任何事，表示成功
false不做任何事，总是返回退出状态码1
：命令，总是返回退出状态码0

 1 while:
  2 do
  3   echo "Do something.."
  4   echo "Hit [ CTRL+C ] to stop!"
  5   sleep 3
  6 done

一个样例while脚本

1 while :
  2 do
  3   clear #清理终端屏幕
  4
  5   echo "=========================================="
  6   echo "             MAIN - MENU                  "
  7   echo "=========================================="
  8   echo "1. Display date and time."
  9   echo "2. Display system information."
 10   echo "3. Display what users are doing."
 11   echo "4. Exit"
 12
 13   read -p "Enter your choice [ 1 - 4 ]: " choice
 14
 15   echo $choice
 16
 17   case $choice in
 18   1)
 19     echo "Today is $(date +%Y-%m-%d)."
 20     echo "Current time: $(date +%H:%M:%S)"
 21     read -p "Press [Enter] key to continue..." readEnterKey
 22     ;;
 23   2)
 24     uname -a
 25     read -p "Press [Enter] key to continue..." readEnterKey
 26     ;;
 27   3)
 28     w
 29     read -p "Press [Enter] key to continue..." readEnterKey
 30     ;;
 31   4)
 32     echo "Bye!"
 33     exit 0
 34     ;;
 35   *)
 36     echo "Error: Invalid option!"
 37     read -p "Press [Enter] key to continue..." readEnterKey
 38     ;;
 39   esac
 40
 41 done