Automatic bash script interaction

Question

I have been trying to make a bash script that interacts with a program.

I need to run "script1" (the program, ie. "./script1.sh"), and i need "script2" (bash script) to be run and read the questions, and respond with answers, back to "script1".

It's the actual interaction between the two script i cannot solve.

Restrictions:

• Use of expect or other similar functions is not allowed, it must be run on linux shell commands.
• script1.sh will launch several randomly generated questions in concession. Each must be answered right.

I have tried using an array of techniques:

• /proc/[pid]/fd/0 (for using stdin, but it seems constricted to terminal and not the shell process itself)
• Using netcat to setup a pipe (This works but leaves me back at square one with regards to the interaction: Reading and replying)
• Using pipes (./script1.sh | the_pipe, but this doesn't allow any input to be given back to "script1")
• Using normal files for input (./script1.sh < answer.txt > question.txt, but it seems that answer.txt is only read once on script start-up?)
• Using named pipes (./script1.sh < answer.pipe > question.pipe, but the script stalls on start because of the answer.pipe blocks it. If i force a carriage return to the answer.pipe to get the process started, "script1" fails, as the carriage return is a wrong answer)
• I have tried using background processes to break down the different tasks (ie. ./script_to_parse_questions.sh &, then saving the result to a file, which is read once and then deleted etc.)

I think "the linux way" might probably be to use pipes "|" or brackets "<>", but it's probably just me who cannot get it working properly.

(Edited for clarification)

Answer 1

This is where you would want to use a bash Coprocess (introduced in bash v4.0 -- NEWS)

Suppose we have a file that contains the questions and answers:

$ cat q_and_a 
Q1
answer one
this is question two
ans 2
question the third
I say thrice

Then "script1" can read this file, ask the questions in random order, and know what the correct answer is:

$ cat script1.sh 
#!/usr/bin/env bash

# read the q_and_a file
qs=()
as=()
while read -r q; read -r a; do
    qs+=( "$q" )
    as+=( "$a" )
done < q_and_a

# ask the questions in random order
readarray -t order < <(
    printf "%d\n" "${!qs[@]}" | shuf
)

for i in "${order[@]}"; do
    echo "${qs[i]}"
    read -r ans
    if [[ $ans == "${as[i]}" ]]; then
        echo "answer to '${qs[i]}' is CORRECT"
    else
        echo "answer to '${qs[i]}' is WRONG"
    fi
done

Now, "script2" can invoke script1 as a coprocess, listen for a question, provide the answer, and then listen for the response to the answer:

$ cat script2.sh 
#!/usr/bin/env bash

# read the q_and_a file
declare -A qa
while read -r q; read -r a; do
    qa[$q]=$a
done < q_and_a

coproc ./script1.sh

for ((i=0; i < ${#qa[@]}; i++)); do
    read -r question <& ${COPROC[0]}
    echo "script1 asked: '$question'"

    echo "answering: '${qa[$question]}'"
    echo "${qa[$question]}" >& ${COPROC[1]}

    read -r response <& ${COPROC[0]}
    echo "script1 responded: '$response'"
done

Running script2 might look like:

$ ./script2.sh
script1 asked: 'this is question two'
answering: 'ans 2'
script1 responded: 'answer to 'this is question two' is CORRECT'
script1 asked: 'question the third'
answering: 'I say thrice'
script1 responded: 'answer to 'question the third' is CORRECT'
script1 asked: 'Q1'
answering: 'answer one'
script1 responded: 'answer to 'Q1' is CORRECT'

Probably in your case, you may not have a shared file with the questions and answers, but you since script2 has the question, you can do what you need to do to analyze it and provide the appropriate answer.