Read stdin for user input when a file is already redirected to stdin [duplicate]

Question

So I'm trying to do something like the following:

while read line; do
    read userInput
    echo "$line $userInput"
done < file.txt

So say file.txt has:

Hello?
Goodbye!

Running the program would create:

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?

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

Answer 1

Instead of using redirection, you can open file.txt to a file descriptor (for example 3) and use read -u 3 to read from the file instead of from 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:

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 -u option for read doesn't work in sh).