Question

我有这个：

while read -r line; do echo "hello $line"; read -p "Press any key" -n 1; done < file

hello This is line 1
hello his is line 2
hello his is line 3
hello his is line 4
hello his is line 5
hello his is line 6
hello his is line 7

为什么我看不到提示“按任意键”？

Answer 1

来自man bash：

-p prompt
   Display prompt on standard error, without a trailing new
   line, before attempting to read any input. The prompt is
   displayed only if input is coming from a terminal.

所以，因为你从文件中读取了行，但没有显示终端提示符。

Answer 2

正如其他人提到的，你没有看到提示，因为当stdin是终端时，bash只打印提示。在您的情况下，stdin是一个文件。

但是这里有一个更大的错误：在我看来，你想要从两个地方读取：文件和用户。你必须做一些重定向魔术来实现这个目标：

# back up stdin
exec 3<&0
# read each line of a file.  the IFS="" prevents read from
# stripping leading and trailing whitespace in the line
while IFS="" read -r line; do
    # use printf instead of echo because ${line} might have
    # backslashes in it which some versions of echo treat
    # specially
    printf '%s\n' "hello ${line}"
    # prompt the user by reading from the original stdin
    read -p "Press any key" -n 1 <&3
done <file
# done with the stdin backup, so close the file descriptor
exec 3<&-

请注意，上述代码不适用于/bin/sh，因为它不符合POSIX标准。你必须使用bash。我建议通过更改提示用户的行来使其符合POSIX标准：

printf 'Press enter to continue' >&2
read <&3

Answer 3

您可以明确地从控制终端/dev/tty读取：

while IFS="" read -r line; do 
   echo "hello $line"
   read -p "Press any key" -n 1 </dev/tty
done < file

当从文件重定向i / p时，读取不提示

3 个答案: