path: root/02_exercise/shell.c

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

#include "array.h"
#include "prompt_utils.h"

int parse_line(char const *line, char ***parts, size_t *part_count);

// returns the return code of the executed program
int exec_command(const char *path, char *const argv[], bool background);

int main(void) {
    setvbuf(stdout, NULL, _IONBF, 0);

    char const *const original_wd = get_current_dir_name();
    char const *prompt = relative_path(original_wd, original_wd);
    bool done = false;
    while (!done) {
        bool bg = false;
        char *line = NULL;
        size_t cap = 0;
        __ssize_t length;

        printf("%s > ", prompt);
        if ((length = getline(&line, &cap, stdin)) < 0) {
            fprintf(stderr, "Failed to read from STDIN");
            exit(-1);
        }

        if (strspn(line, " \n\t") == strlen(line)) {
            continue;
        }

        line[length - 1] = '\0'; // cut the line feed

        char **arguments = NULL;
        size_t argument_count;
        parse_line(line, &arguments, &argument_count);

        if (argument_count <= 0)
            goto clean;

        char *command = arguments[0];
        char *last_arg = arguments[argument_count - 2];

        if (strcmp(last_arg, "&") == 0) {
            bg = true;
            arrayRelease(arguments[argument_count - 2]);
            arguments[argument_count - 2] = NULL;
        }

        if (strcmp(command, "cd") == 0) {
            if (arrayLen(arguments) != 3) {
                fprintf(stderr, "usage: cd <path>");
                goto clean;
            }

            int ret = chdir(arguments[1]);
            if (ret)
                printf("[%i] ", ret);

            free((void *)prompt);
            char const *current_wd = get_current_dir_name();
            prompt = relative_path(original_wd, current_wd);
            free((void *)current_wd);
        } else if (strcmp(command, "exit") == 0) {
            done = true;
        } else {
            int ret = exec_command(command, arguments, bg);
            if (ret)
                printf("[%i] ", ret);
        }

        clean:
        free((void *)line);
        while (arrayLen(arguments) > 0) {
            char *tmp = arrayPop(arguments);
            if (tmp)
                arrayRelease(tmp);
        }
        arrayRelease(arguments);
    }

    free((void *)original_wd);
    free((void *)prompt);
}

int parse_line(char const *line, char ***parts, size_t *part_count) {
    char *part;
    char **local_parts;

    if (arrayInit(part) != 0 || arrayInit(local_parts) != 0) {
        fprintf(stderr, "Failed to prepare new part / parts array whilst parsing line");
        return -1;
    }

    for (size_t i = 0; i < strlen(line) + 1; ++i) {
        char c = line[i];
        if (c == ' ' || c == '\0') {
            if (arrayLen(part) == 0)
                continue;
            arrayPush(part) = '\0';
            arrayPush(local_parts) = part;
            if (c == '\0') {
                arrayPush(local_parts) = NULL;
                break;
            } else {
                arrayInit(part);
            }
        } else {
            arrayPush(part) = c;
        }
    }

    *part_count = arrayLen(local_parts);
    *parts = local_parts;

    return 0;
}

int exec_command(const char *path, char *const argv[], bool background) {
    int  pid;
    int  pipefd[2];
    int  status;
    char buf[512];

    pipe(pipefd);
    if ((pid = fork()) == 0) {
        close(pipefd[0]);
        dup2(pipefd[1], 1);
        close(pipefd[1]);
        execvp(path, argv);
        fprintf(stderr, "could not execute \"%s\"\n", path);
        fflush(stderr);
        exit(-1);
    }

    if (pid < 0) {
        fprintf(stderr, "no fork\n");
        exit(-2);
    }

    close(pipefd[1]);

    int new_pid;
    if (background) {
        new_pid = fork();
    }

    if (!background || new_pid == 0) {
        if (background)
            printf("[%i]\n", pid);

        __ssize_t length;
        while ((length = read(pipefd[0], buf, 10)) > 0) {
            buf[length] = '\0';
            printf("%s", buf);
        }

        waitpid(pid, &status, 0);

        if (background) {
            printf("[%i] TERMINATED\n", pid);
            printf("[%i] EXIT STATUS: %i\n", pid, status);
            exit(0);
        }
    }

    close(pipefd[0]);

    return WEXITSTATUS(status);
}