从文件重定向i/p时不提示读取

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

引用自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，因为您是从文件中读取行，而不是从终端提示符中读取行。

Answer 2

正如其他人提到的，您看不到提示符，因为bash仅在stdin是终端时才打印提示符。在您的例子中，stdin是一个文件。

但是这里有一个更大的bug :在我看来，你想要从两个地方读取:文件和用户。你将不得不做一些重定向魔术来完成这件事：

# 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，上面的代码不能与/bin/sh一起使用，因为它不符合POSIX。你必须使用bash。我建议通过更改提示用户的行使其符合POSIX：

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

Answer 3

您可以显式地从控制终端/dev/tty读取

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