microshell_project/main.c

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

#define MAX_SIZE 1024

// int LogCommandHistory(char* buf, char** command_log, int n) {
//     command_log[n] = buf;
// }

void PrintCurrentDir() { // pwd
    char cwd[MAX_SIZE];
    if (getcwd(cwd, sizeof(cwd)) != NULL) {
        printf("[%s] $ ", cwd);
    } else {
        perror("getcwd() error");
    }
}

int ChangeDirectory(char** args) { // cd
    args++; // Moving pointer to the next element (cd requires local or global path, the first argument is command name, so it's skipped)
    char* path = args[0];
    if (path == NULL || strcmp(path, "~") == 0) {
        path = getenv("HOME");
    }
    if (chdir(path) != 0) {
        perror("cd");
        return -1;
    }
    return 0;
}

void PrintHelp() { // help
    printf("C Microshell implementation by Maciej Życzyński\n");
}

int HandleBuiltInCommands(char* command, char** args) { // Manual implementation of commands unsupported by execvp()
    if (strcmp(command, "cd") == 0) {
        ChangeDirectory(args);
        return 1;
    }
    else if (strcmp(command, "help") == 0) {
        PrintHelp();
        return 1;
    }
    else if (strcmp(command, "exit") == 0) {
        return 2;
    }
    return 0;
}

int HandleCommand(char* command, char** args) { // Execute commands supported by execvp()
    if (execvp(command, args) == -1) {
        perror("Error executing command");
        return -1;
    }
    return 0;
}

int ParseCommand(char* buf, char** command, char** args) {
    char buf_cp[MAX_SIZE];
    strcpy(buf_cp, buf); // Leave the original buffer (important for command history implementation)
    buf_cp[strlen(buf_cp) - 1] = '\0'; // Remove newline from input string

    char* token = strtok(buf_cp, " ");
    int tok_count = 0;

    if (token == NULL) { // Retrieve command and arguments
        return -1;
    }
    *command = token;

    while (token != NULL) {
        args[tok_count] = token;
        tok_count++;
        token = strtok(NULL, " ");
    }
    args[tok_count] = NULL; // Manually add NULL at the end (execvp() requires the argument array to be null-terminated)

    return 0;
}

int main() {
    char buf[MAX_SIZE];
    char* command_log[MAX_SIZE];
    int n = 0;

    while (1) {
        PrintCurrentDir();

        char* command;
        char* args[MAX_SIZE];
        fgets(buf, sizeof(buf), stdin);
        
        if (ParseCommand(buf, &command, args) < 0) {
            printf("Invalid command\n");
            continue;
        }

        // LogCommandHistory(buf, &command_log, n);
        // n++;

        int handler_value = HandleBuiltInCommands(command, args);
        if (handler_value == 2) { // Exit command
            break;
        }
        else if (handler_value == 0) { // Not a built-in command

            // Forking logic
            pid_t pid = fork();
            if (pid < 0) {
                perror("Error while forking\n");
            }
            else if (pid == 0) { // Child process
                if (HandleCommand(command, args) == -1) {
                    exit(EXIT_FAILURE);
                }
                exit(EXIT_SUCCESS);
            }
            else { // Parent process
                int status;
                if (waitpid(pid, &status, 0) == -1) {
                    perror("Error with parent process\n");
                }
            }
        }
    }

    return 0;
}