Question

I’m sure this is an easy question, but in creating a mock shell in C++, there is one aspect of the project that I don’t quite understand.

Basically, we’re creating a program called myShell, invoked with the command “./myShell”. That will open up the custom shell, but what I want to be able to do, is call external functions right from the command with the token “-c”.

For example, the command: “./myShell -c ls -l” will call the linux ls function. I can do this once the program is actually invoked, but not before (i.e. opening ./myShell, then typing ls -l”.

I’m new to processes, and any help would be appreciated.

Answer 1

You have code that waits for user input, interprets the commands that it reads from the user, runs them, and goes back to waiting for user input in a loop, like this pseudocode:

int main(int argc, char *argv[]) {
    bool must_exit = false;
    while (!must_exit) {
        string input = read_user_input();
        must_exit = interpret_and_run(input);
    }
    return 0;
}

Modify your function to concatenate argvs and run them before entering the loop:

int main(int argc, char *argv[]) {
    bool must_exit = false;
    if (argc > 2 && !strcmp(argv[1], "-c")) {
        string input = concatenate(argv); // From 1 to N, not from 0 to N
        must_exit = interpret_and_run(input);
    }
    while (!must_exit) {
        string input = read_user_input();
        must_exit = interpret_and_run(input);
    }
    return 0;
}