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>
#include <termios.h>

#define MAX_SIZE 1024
#define HISTORY_SIZE 5

// RAW TERMINAL INPUT / LOGGING HISTORY IMPLEMENTATION -----------

// Global variable for termios
struct termios orig_termios;

// Termios functions
void EnableRawMode(struct termios* orig_termios) {
    struct termios raw = *orig_termios;
    raw.c_lflag &= ~(ECHO | ICANON);
    tcsetattr(STDIN_FILENO, TCSAFLUSH, &raw);
}

void DisableRawMode(struct termios* orig_termios) {
    tcsetattr(STDIN_FILENO, TCSAFLUSH, orig_termios);
}

void DisableRawModeWrapper() {
    DisableRawMode(&orig_termios);
}

int LogCommandHistory(char* buf, char** command_log, int* n) {
    int index = *n % HISTORY_SIZE;
    int prev_index = (*n == 0) ? HISTORY_SIZE - 1 : (*n - 1) % HISTORY_SIZE;

    if (command_log[prev_index] != NULL && strcmp(buf, command_log[prev_index]) == 0) {
        return 0;
    }
    if (command_log[index] != NULL) {
        free(command_log[index]);
    }

    command_log[index] = strdup(buf);
    (*n)++;

    return 0;
}

void FreeCommandHistory(char** command_log) {
    for (int i = 0; i < HISTORY_SIZE; i++) {
        if (command_log[i] != NULL) {
            free(command_log[i]);
        }
    }
}

void ClearBufferContent(int length) { // Function to clear buffer
    for (int i = 0; i < length; i++) {
        printf("\b \b");
    }
}

// Get raw input from terminal + arrow key history navigation
void GetRawInput(char* buf, char** command_log, int n) {
    int index = n % HISTORY_SIZE;
    int history_counter = 0;
    int pos = 0;
    char c;

    while (1) {
        c = getchar();

        if (c == '\n') { // Enter key
            buf[pos] = '\0';
            printf("\n");
            return;
        } else if (c == 127 || c == '\b') { // Backspace
            if (pos > 0) {
                pos--;
                buf[pos] = '\0';
                printf("\b \b");
            }
        } else if (c == '\033') { // Inputting arrow keys
            getchar(); // Skip '[' character
            char arrow = getchar();

            if (arrow == 'A') { // Up arrow
                int prev_index = (index == 0) ? HISTORY_SIZE - 1 : (index - 1) % HISTORY_SIZE;
                if (command_log[prev_index] != NULL) {
                    ClearBufferContent(pos); // Clear current buffer
                    index = (index == 0) ? HISTORY_SIZE - 1 : index - 1;
                    history_counter++;

                    strcpy(buf, command_log[index]);
                    printf("%s", buf);
                    pos = strlen(buf);
                }
            }
            else if (arrow == 'B') { // Down arrow
                if (history_counter > 0) {
                    index = (index + 1) % HISTORY_SIZE;
                    history_counter--;
                    ClearBufferContent(pos);
                    if (history_counter == 0) {
                        buf[0] = '\0'; // Clear buffer
                        pos = 0;
                    } else {
                        strcpy(buf, command_log[index]);
                        printf("%s", buf);
                        pos = strlen(buf);
                    }
                }
            }
        } else { // Regular character
            if (pos < MAX_SIZE - 1) {
                buf[pos++] = c;
                buf[pos] = '\0';
                printf("%c", c);
            }
        }
    }
}


// MAIN MICROSHELL FUNCTIONS -----------

char* GetCurrentUserAndDir() { // return current user + working directory
    char cwd[MAX_SIZE];
    if (getcwd(cwd, sizeof(cwd)) == NULL) {
        perror("getcwd() error");
        return NULL;
    }
    char* user = getenv("USER");
    if (user == NULL) {
        perror("getenv() error");
        return NULL;
    }

    size_t result_size = strlen(user) + strlen(cwd) + 7; // Allocate memory (include extra space for format characters)
    char* result = (char*)malloc(result_size);

    snprintf(result, result_size, "[%s@%s] $ ", user, cwd); // Format the prompt string

    return result;
}

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("-------------------------------------------------\n");
    printf("C Microshell implementation by Maciej Życzyński\n");
    printf("\"exit\" - exit the program\n");
    printf("\"help\" - display this menu\n");
    printf("Other bash commands work accordingly in child processes\n");
    printf("-------------------------------------------------\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) {
        printf("Error executing command\n");
        return -1;
    }
    return 0;
}

int ParseCommand(char* buf, char** command, char** args) { // Parse input string into command and array of arguments
    char buf_cp[MAX_SIZE];
    strcpy(buf_cp, buf); // Leave the original buffer (important for command history implementation)

    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;
    char* args[MAX_SIZE];
    int n = 0;
    char* command_log[HISTORY_SIZE] = {NULL};
    
    // Save original terminal settings and restore them on exit
    if (tcgetattr(STDIN_FILENO, &orig_termios) == -1) {
        perror("tcgetattr() error");
        return 1;
    }
    atexit(DisableRawModeWrapper); // call DisableRawModeWrapper when program exits

    while (1) {
        char* prompt = GetCurrentUserAndDir(); // Display prompt
        if (prompt != NULL) {
            printf("%s", prompt);
            free(prompt);
        }

        EnableRawMode(&orig_termios);
        GetRawInput(buf, command_log, n);
        DisableRawMode(&orig_termios);
        

        if (ParseCommand(buf, &command, args) < 0) { // Parse buffer input
            printf("Invalid command\n");
            continue;
        }

        LogCommandHistory(buf, command_log, &n); // Add buffer to logging history

        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");
                }
            }
        }
    }

    FreeCommandHistory(command_log);
    return 0;
}