main() {
    char *prog = NULL;
    char **args = NULL;

    // Read the input a line at a time, and parse each line into the program 
    // name and its arguments. End loop if we've reached the end of the input.
    while (readAndParseCmdLine(&prog, &args)) {		

        // Create a child process to run the command.
        int child_pid = fork();		

        if (child_pid == 0) {   	
            // I'm the child process. 
            // Run program with the parent's input and output.
            exec(prog, args);
            // NOT REACHED
        } else {			
            // I'm the parent; wait for the child to complete.
            wait(child_pid); 		
            return 0;
        }
    }
}