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