path: root/02_exercise/shell.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <sys/wait.h>
#include <unistd.h>

#include "array.h"
#include <stdbool.h>

void print_prompt();

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

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

int main(int argc, char* argv[]) {
    while (true) {
        char *line = NULL;
        size_t cap = 0;
        size_t length = 0;

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

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

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

        if (strcmp(exe, "cd") == 0) {
            printf("Changing dirs \n");
            chdir("beispiele");
        } else if (strcmp(exe, "exit") == 0) {
            exit(0);
        } else {
            exec_command(exe, arguments, 0);
        }
        free((void *)line);
        // no need to free exe, since it is part of arguments any way
        arrayRelease(arguments);
    }
}

int parse_line(char const *line, char **exe, 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 array");
        exit(-1);
    }

    bool found_exe = false;
    char c;
    int i = 0;
    while (true) {
        c = line[i++];
        if (c == ' ' || c == '\0') {
            arrayPush(part) = '\0';
            arrayPush(local_parts) = part;
            if (!found_exe) {
                // the first is the executable
                *exe = malloc(arrayLen(part) * sizeof(char));
                strcpy(*exe, part);
                found_exe = true;
            }
            arrayInit(part);
            if (c == '\0') {
                arrayPush(local_parts) = NULL;
                break;
            }
        } else {
            arrayPush(part) = c;
        }
    }

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

    return 0;
}

void print_prompt() {
    size_t length  = 1024;
    char   *buffer = malloc(length * sizeof(char));
    getcwd(buffer, length);
    if (buffer == NULL) {
        printf(".> ");
    } else {
        printf("%s > ", buffer);
    }
}

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

    pipe(pipefd);
    if ((pid = fork()) == 0) {
        close(pipefd[0]);
        dup2(pipefd[1], 1); // includes close(1);
        close(pipefd[1]);
        execvp(path, argv);
        fprintf(stderr, "no program\n");
        exit(-1);
    }

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

    close(pipefd[1]);

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

    waitpid(pid, &status, 0);

    close(pipefd[0]);

    return WEXITSTATUS(status);
}