main.c

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

#define BUFFER_SIZE 256
#define MAX_COMMAND_LENGTH 100

ssize_t custom_getline(char **lineptr, size_t n) {
    if (*lineptr == NULL || n == 0) {
        *lineptr = (char *)malloc(BUFFER_SIZE);
        if (*lineptr == NULL) {
            perror("malloc");
            return -1;
        }
        n = BUFFER_SIZE;
    }

    ssize_t bytesRead = read(STDIN_FILENO, *lineptr, n);

    if (bytesRead == -1) {
        perror("read");
        return -1;
    }

    return bytesRead;
}

void executeCommand(const char *command, char *const args[]) {
    pid_t pid = fork();

    if (pid == -1) {
        perror("fork");
        exit(EXIT_FAILURE);
    } else if (pid == 0) { // Child process
        execvp(command, args);
        perror("execvp");
        exit(EXIT_FAILURE);
    } else { // Parent process
        int status;
        waitpid(pid, &status, 0);

        if (WIFEXITED(status)) {
            printf("Exit Status: %d\n", WEXITSTATUS(status));
        } else {
            printf("Error executing command '%s'.\n", command);
        }
    }
}

void handleCd(const char *directory) {
    if (chdir(directory) != 0) {
        perror("chdir");
        fprintf(stderr, "Error changing directory to '%s'.\n", directory);
    } else {
        printf("Changed directory to '%s'.\n", directory);
    }
}

void handleSetenv(char *const args[]) {
    if (args[1] != NULL && args[2] != NULL && args[3] == NULL) {
        if (setenv(args[1], args[2], 1) != 0) {
            perror("setenv");
            fprintf(stderr, "Error setting environment variable '%s'.\n", args[1]);
        } else {
            printf("Environment variable '%s' set to '%s'.\n", args[1], args[2]);
        }
    } else {
        fprintf(stderr, "Usage: setenv <variable> <value>\n");
    }
}

void handleUnsetenv(char *const args[]) {
    if (args[1] != NULL && args[2] == NULL) {
        if (unsetenv(args[1]) != 0) {
            perror("unsetenv");
            fprintf(stderr, "Error unsetting environment variable '%s'.\n", args[1]);
        } else {
            printf("Environment variable '%s' unset.\n", args[1]);
        }
    } else {
        fprintf(stderr, "Usage: unsetenv <variable>\n");
    }
}

int tokenizeInput(char *line, char *args[]) {
    int arg_count = 0;
    char *token = strtok(line, " \t\n");

    while (token != NULL) {
        args[arg_count++] = token;
        token = strtok(NULL, " \t\n");
    }

    args[arg_count] = NULL;

    return arg_count;
}

void handleCommand(char *line) {
    char *args[MAX_COMMAND_LENGTH];
    int arg_count;

    while (1) {
        printf("Enter a command: ");
        fflush(stdout);

        ssize_t bytesRead = custom_getline(&line, BUFFER_SIZE);

        if (bytesRead == -1) {
            fprintf(stderr, "Error reading input.\n");
            break;
        } else if (bytesRead == 0) {
            printf("End of file reached.\n");
            break;
        }

        arg_count = tokenizeInput(line, args);

        if (arg_count > 0) {
            if (strcmp(args[0], "exit") == 0) {
                free(line);
                exit(EXIT_SUCCESS);
            } else if (strcmp(args[0], "cd") == 0) {
                if (args[1] != NULL) {
                    handleCd(args[1]);
                } else {
                    fprintf(stderr, "Usage: cd <directory>\n");
                }
            } else if (strcmp(args[0], "mkdir") == 0) {
                if (args[1] != NULL) {
                    char *mkdir_args[] = {"mkdir", args[1], NULL};
                    executeCommand("/bin/mkdir", mkdir_args);
                } else {
                    fprintf(stderr, "Usage: mkdir <directory>\n");
                }
            } else if (strcmp(args[0], "setenv") == 0) {
                handleSetenv(args);
            } else if (strcmp(args[0], "unsetenv") == 0) {
                handleUnsetenv(args);
            } else if (strcmp(args[0], "ls") == 0) {
                executeCommand("/bin/ls", args);
            } else if (strcmp(args[0], "pwd") == 0) {
                char cwd[1024];
                if (getcwd(cwd, sizeof(cwd)) != NULL) {
                    printf("Current working directory: %s\n", cwd);
                } else {
                    perror("getcwd");
                }
            } else if (strcmp(args[0], "env") == 0) {
                executeCommand("/usr/bin/env", args);
            } else {
                executeCommand(args[0], args);
            }
        }
    }

    free(line);
}

int main() {
    char *line = NULL;

    handleCommand(line);

    printf("Exiting CLI program.\n");

    return 0;
}