bash: Prompting for user input while reading file

Question

I'm working on a bash script that parses a tab separated file. If the file contains the word "prompt" the script should ask the user to enter a value.

It appears that while reading the file, the "read" command is not able to read from standard input as the "read" is simply skipped.

Does anybody have a work around for doing both reading from a file as well as from stdin?

Note: The script should run on both Git Bash and MacOS.

Below is a little code example that fails:

#!/bin/bash #for debugging set "-x" while IFS=$'\r' read -r line || [[ -n "$line" ]]; do [[ -z $line ]] && continue IFS=$'\t' read -a fields <<<"$line" command=${fields[0]} echo "PROCESSING "$command if [[ "prompt" = $command ]]; then read -p 'Please enter a value: ' aValue echo else echo "Doing something else for "$command fi done < "$1" 

Output:

$ ./promptTest.sh promptTest.tsv + IFS=$'\r' + read -r line + [[ -z something else ]] + IFS=' ' + read -a fields + command=something + echo 'PROCESSING something' PROCESSING something + [[ prompt = something ]] + echo 'Doing something else for something' Doing something else for something + IFS=$'\r' + read -r line + [[ -z prompt ]] + IFS=' ' + read -a fields + command=prompt + echo 'PROCESSING prompt' PROCESSING prompt + [[ prompt = prompt ]] + read -p 'Please enter a value: ' aValue + echo + IFS=$'\r' + read -r line + [[ -n '' ]] 

Sample tsv file:

$ cat promptTest.tsv something else prompt otherthing nelse 

Answer 1

The simplest way is to use /dev/tty as the read for keyboard input.

For example:

#!/bin/bash echo hello | while read line do echo We read the line: $line echo is this correct? read answer < /dev/tty echo You responded $answer done 

This breaks if you don't run this on a terminal, and wouldn't allow for input to be redirected into the program, but otherwise works pretty well.

More generally, you could take a new file handle based off the original stdin, and then read from that. Note the exec line and the read

#!/bin/bash exec 3<&0 echo hello | while read line do echo We read the line: $line echo is this correct? read answer <&3 echo You responded $answer done 

In both cases the program looks a bit like:

% ./y We read the line: hello is this correct? yes You responded yes 

The second variation allows for input to also be redirected

% echo yes | ./y We read the line: hello is this correct? You responded yes 

Answer 2

This SO Q&A titled: How to read from a file or stdin in Bash? shows this method which highlights how to do what it sounds like you're looking for:

while read line do echo "$line" done < "${1:-/dev/stdin}" 

Answer 3

You can dup standard input before you do the redirection.

#!/bin/bash # Assuming here fd 4 is unused. Dup file descriptor 0 (stdin) to # file descriptor 4 exec 4<&0 while read x; do # Read from stdin (the file b/c of redirect below) echo "From $1: $x" read y <&4 # Read from file descriptor 4 (the original stdin) echo "From keyboard: $y" done < "$1"