Reading all of stdin at program start prevents reading from stdin during the program

Question

I have a golang program that makes a simple repl for jq. I'd like to be able to read input from stdin at program start into a temporary file, so I can use the repl with piped input.

cat file.json | jqrepl

However, when I read from stdin, either using a scanner or a reader, I reach the EOF for stdin, and then I can no longer accept input from stdin for the main repl loop. Readline fails immediately because it's at EOF.

I've tried deferring a Reader.UnreadByte, Closing the scanner, and a multitude of "seek(0)", and other raw operations on stdin.

Is there a way to reset the stdin so that it can be read from again? Ideally I would read until EOF, save that to a temporary file, and then enter the repl mode.

Thanks!

Answer 1

(I suppose the stdin you mentioned as in "I can no longer accept input from stdin for the main repl loop" is referring to the interactive user input.)

Try like this:

[STEP 101] # cat foo.sh
while read line; do
    printf '> %s\n' "$line"
done

# close stdin
exec 0<&-
# reopen stdin to /dev/tty
exec 0< /dev/tty

read -p 'Input something: ' v
printf 'You inputted: %s\n' "$v"
[STEP 102] # printf '%s\n' foo bar | bash ./foo.sh
> foo
> bar
Input something: hello world
You inputted: hello world
[STEP 103] #