Fork and Execute

build_fork_execve_example.sh

#!/usr/bin/env bash

gcc -o fork_execve_example fork_execve_example.c

chmod +x ./fork_execve_example 
chmod +x ./test_script.sh

fork_execve_example.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/wait.h>
#include <time.h>

int main() {
    // Seed the random number generator with the current time
    srand(time(0));

    // Generate a random value between 0 and RAND_MAX
    int randomValue = rand();
    int randomValue2 = rand();

    char *local_var = "IamLocal";
    char randomValueStr[40];
    snprintf(randomValueStr, sizeof(randomValueStr), "%d-%d", randomValue, randomValue2);

    // Print the random value as a string
    printf("Random value as string: %s\n", randomValueStr);

    // Step 1: Read the environment variable "MY_VAR"
    char *env_var = getenv("MY_VAR");
    if (env_var != NULL) {
        printf("Original MY_VAR: %s\n", env_var);
    } else {
        printf("MY_VAR is not set\n");
    }

    // Step 2: Modify the environment variable value
    char new_value[256];
    snprintf(new_value, sizeof(new_value), "[DEBUG][MY_VAR][VALUE] Modified_%s", env_var ? env_var : "default");

    // Step 3: Set the modified environment variable
    setenv("MY_VAR", new_value, 1); // 1 means overwrite the existing value
    printf("New MY_VAR: %s\n", getenv("MY_VAR"));

    // Step 4: Fork the process
    pid_t pid = fork();

    if (pid == -1) {
        perror("fork failed");
        exit(EXIT_FAILURE);
    } else if (pid == 0) {
        // Child process
        printf("Child process is executing ahihi...\n");
	printf("....... Check point 00\n");
	char *test = "How are you";
	printf("....... Check point 01: %s \n", test);
	char *child_var_1 = getenv("MY_VAR");
	printf("....... Check point 02 \n");
	printf("....... Check point 03: %s \n", child_var_1);

	
        // Step 5: Execute an external shell script using execve
        char *argv[] = {"./test_script.sh", NULL}; // Arguments for the shell script
	printf("....... Check point 04 \n");

        char *envp[] = {NULL}; // You can pass the modified environment or use the current environment
        printf(".......... Check point 05 \n");
	
	printf(".......... Check point 06: %s - %s \n", local_var, randomValueStr);
	char *child_var = getenv("MY_VAR");
	if (child_var == NULL) { child_var = "EMPTY"; }
	
	printf(".......... MY_VAR retrieved by the forked process: %s \n", child_var);
	sleep(3);
        if (execve("./test_script.sh", argv, envp) == -1) {
            perror("execve failed");
            exit(EXIT_FAILURE);
        }
    } else {
        // Parent process
        int status;
        waitpid(pid, &status, 0); // Wait for the child process to complete
        printf("Parent process: Child process finished with status %d\n", status);
    }

    return 0;
}

test_script.sh

#!/usr/bin/env bash

echo "Running test_script.sh"
echo "MY_VAR is: $MY_VAR"