How to run a continuous bash program and have C start it, get input, and send it output, then gets it's input and then send it output

I've searched around and couldn't quite find and answer to this.

I'm trying to get C to open a bash program called L.

The I want to be able to run the program using something close to system or popen.

Except I want to have the same program running in the back ground and able to make calls to the same program so that it doesn't lose it's memory or history.

Something like this:

// Open program

// Send Hello Program to program

// Get Hello Programer from program

// Send What did I send you to program

// Get Hello Program from program

Here is how to open a bash program in the background and communicate with it from a C program:

C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int main() {
    FILE *fp;
    char path[1035];

    // Open the process "L" for reading and writing
    fp = popen("./L", "r+");
    if (fp == NULL) {
        printf("Failed to run command\n");
        exit(1);
    }

    // Send "Hello Program" to the program
    fprintf(fp, "Hello Program\n");
    fflush(fp);

    // Read the response from the program
    fgets(path, sizeof(path), fp);
    printf("Get %s", path);

    // Send "What did I send you" to the program
    fprintf(fp, "What did I send you?\n");
    fflush(fp);

    // Read the response from the program
    fgets(path, sizeof(path), fp);
    printf("Get %s", path);

    // Close the process
    pclose(fp);
    return 0;
}

Code

#!/bin/bash

memory=""

while true
do
    read input
    if [[ "$input" == "What did I send you?" ]]
    then
        echo "$memory"
    else
        memory="$input"
        echo "$input"er
    fi
done

To compile the C code:

Code

gcc -o main main.c

To run the C code:

Code

./main