rsh.c

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

#define N 12

extern char **environ;

char *allowed[N] = {"cp", "touch", "mkdir", "ls", "pwd", "cat",
					"grep", "chmod", "diff", "cd", "exit", "help"};

int isAllowed(const char* cmd) {
	for(int i = 0; i < N; i++) {
		if(strcmp(cmd, allowed[i]) == 0) return 1;
	}
	printf("NOT ALLOWED!\n");

	return 0;
}

int spawnProcess(char* const* argv) {
	pid_t pid;
    int status;
    posix_spawnattr_t attr;

    // Initialize spawn attributes
    posix_spawnattr_init(&attr);

    // Set flags if needed, for example, to specify the scheduling policy
    // posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSCHEDULER);

    // Spawn a new process
    if (posix_spawnp(&pid, argv[0], NULL, &attr, argv, environ) != 0) {
        perror("spawn failed");
        exit(EXIT_FAILURE);
    }

    // Wait for the spawned process to terminate
    if (waitpid(pid, &status, 0) == -1) {
        perror("waitpid failed");
        exit(EXIT_FAILURE);
    }

    if (WIFEXITED(status)) {
        // printf("Spawned process exited with status %d\n", WEXITSTATUS(status));
    }

    // Destroy spawn attributes
    posix_spawnattr_destroy(&attr);

    return EXIT_SUCCESS;
}

int main() {
    char line[256];

    while (1) {
		fprintf(stderr, "rsh>");

		if (fgets(line, 256, stdin)==NULL) continue;

		if (strcmp(line, "\n") == 0) continue;

		line[strlen(line)-1] = '\0';

		char* argv[20] = {NULL};
		// Parse input command
		int i = 0;
        char* token = strtok(line, " ");
		while (token != NULL && i < 20) {
			argv[i] = token;
			i++;
			token = strtok(NULL, " ");
		}

		if (isAllowed(argv[0]) == 0) continue;

		// printf("{");
		// for(i = 0; i < 19; i++) {
		// 	printf("\"%s\",",argv[i]);
		// }
		// printf("\"%s\"}\n", argv[19]);

		// Spawn processes for the first 9 commands
		for(int i = 0; i < 9; i++) {
			if(strcmp(argv[0], allowed[i]) == 0) {
				spawnProcess(argv);
				break;
			}
		}

		// cd
		if(strcmp(argv[0], "cd") == 0) {
			if(argv[2] != NULL) {
				printf("-rsh: cd: too many arguments\n");
				continue;
			}
			chdir(argv[1]);
		}

		// exit
		if(strcmp(argv[0], "exit") == 0) {
			return 0;
		}

		// help
		if(strcmp(argv[0], "help") == 0) {
			printf("The allowed commands are:\n"
				"1: cp\n"
				"2: touch\n"
				"3: mkdir\n"
				"4: ls\n"
				"5: pwd\n"
				"6: cat\n"
				"7: grep\n"
				"8: chmod\n"
				"9: diff\n"
				"10: cd\n"
				"11: exit\n"
				"12: help\n");
		}

    }
    return 0;
}