Luna/apps/src/sh.c

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

static int status;

typedef struct
{
    char* buffer;
    size_t size;
    size_t capacity;
} command;

void show_prompt()
{
    printf("[%ld]> ", getpid());
}

int command_matches(command* cmd, const char* string)
{
    if (cmd->size <= strlen(string)) // cmd->size includes null terminator
        return 0;
    return strncmp(cmd->buffer, string, strlen(string)) == 0;
}

int command_matches_exactly(command* cmd, const char* string)
{
    if (cmd->size <= strlen(string)) // cmd->size includes null terminator
        return 0;
    if (cmd->size > (strlen(string) + 1)) return 0;
    return strncmp(cmd->buffer, string, strlen(string)) == 0;
}

int command_match_builtins(command* cmd)
{
    if (command_matches(cmd, "exit ")) { exit(atoi(cmd->buffer + 5)); }
    if (command_matches_exactly(cmd, "exit")) { exit(0); }
    if (command_matches_exactly(cmd, "pid"))
    {
        printf("pid %ld, ppid %ld\n", getpid(), getppid());
        return 1;
    }
    return 0;
}

void command_expand(command* cmd, long new_capacity)
{
    char* buffer = realloc(cmd->buffer, new_capacity);
    if (!buffer)
    {
        perror("realloc");
        exit(1);
    }
    cmd->buffer = buffer;
    cmd->capacity = new_capacity;
}

void command_push(command* cmd, char c)
{
    if (cmd->size == cmd->capacity) command_expand(cmd, cmd->capacity + 8);
    cmd->buffer[cmd->size] = c;
    cmd->size++;
}

void command_pop(command* cmd)
{
    cmd->size--;
}

void command_init(command* cmd)
{
    cmd->buffer = malloc(5);
    cmd->capacity = 5;
    cmd->size = 0;
}

void command_clear(command* cmd)
{
    free(cmd->buffer);
    return command_init(cmd);
}

void command_execute(command* cmd)
{
    command_push(cmd, '\0');
    if (command_match_builtins(cmd))
    {
        command_clear(cmd);
        show_prompt();
        return;
    }
    pid_t child = fork();
    if (child < 0)
    {
        perror(cmd->buffer);
        command_clear(cmd);
        show_prompt();
        return;
    }
    if (child == 0)
    {
        execv(cmd->buffer, NULL);
        perror(cmd->buffer);
        exit(127);
    }
    pid_t result;
    while ((result = waitpid(child, &status, 0)) == 0) { msleep(20); }
    if (result < 0)
    {
        perror("waitpid");
        command_clear(cmd);
        show_prompt();
        return;
    }
    int exit_status = WEXITSTATUS(status);
    if (exit_status == -2 || exit_status == -3) printf("(PID %ld) Segmentation fault\n", result);
    else if (exit_status)
        printf("Exited with code %d\n", WEXITSTATUS(status));
    command_clear(cmd);
    show_prompt();
}

void command_concat(command* cmd, const char* str)
{
    while (*str)
    {
        putchar(*str);
        if (*str == '\b') { command_pop(cmd); }
        else if (*str == '\n') { command_execute(cmd); }
        else
            command_push(cmd, *str);
        str++;
    }
}

int main()
{
    show_prompt();

    char buffer[33];

    command shell_command;
    command_init(&shell_command);

    while (1)
    {
        size_t nread = fread(buffer, sizeof(buffer) - 1, 1, stdin);
        if (ferror(stdin))
        {
            perror("fread");
            return 1;
        }
        if (feof(stdin))
        {
            clearerr(stdin);
            msleep(20);
            continue;
        }
        buffer[nread] = 0;
        command_concat(&shell_command, buffer);
    }
}