bash 当文件已重定向到 stdin 时，读取用户输入的 stdin
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Read stdin for user input when a file is already redirected to stdin
提问by Aram Papazian
So I'm trying to do something like the following:
所以我正在尝试执行以下操作：
while read line; do
read userInput
echo "$line $userInput"
done < file.txt
So say file.txt has:
所以说 file.txt 有：
Hello?
Goodbye!
Running the program would create:
运行该程序将创建：
Hello?
James
Hello? James
Goodbye!
Farewell
Goodbye! Farewell
The issue (naturally) becomes that the userinput read reads from stdin which in our case is file.txt. Is there a way to change where it's reading from temporarily to the terminal in order to grab user input?
问题（自然）变成了用户输入读取从 stdin 读取，在我们的例子中是 file.txt。有没有办法将它从临时读取的位置更改为终端以获取用户输入？
Note: The file I am working with is 200,000 lines long. and each line is about 500 chars long. So keep that in mind if needed
注意：我正在处理的文件有 200,000 行。每行大约 500 个字符长。所以如果需要，请记住这一点
回答by jcollado
Instead of using redirection, you can open file.txtto a file descriptor (for example 3) and use read -u 3to read from the file instead of from stdin:
您可以打开file.txt文件描述符（例如 3）而不是使用重定向，并使用read -u 3从文件中读取而不是从stdin：
exec 3<file.txt
while read -u 3 line; do
echo $line
read userInput
echo "$line $userInput"
done
Alternatively, as suggested by Jaypal Singh, this can be written as:
或者，按照 Jaypal Singh 的建议，这可以写为：
while read line <&3; do
echo $line
read userInput
echo "$line $userInput"
done 3<file.txt
The advantage of this version is that it also works in sh(the -uoption for readdoesn't work in sh).
此版本的优点是它也适用于sh（的-u选项在read中不起作用sh）。
