microshell.c

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

enum {
	READ,
	WRITE
};
enum {
	CHILD,
};

void	ft_putstr_fd(char *str, int fd) {
	int	len = 0;
	
	while (str[len])
		len++;
	write(fd, str, len);
}

void	fatal_err() {
	ft_putstr_fd("error: fatal\n", 2)
	exit(1);
}

void	exec_cmd(char **cmd, char **env, int *pipe_fd, int *prev_pipe_read) {
	if (cmd && cmd[0] && env && pipe_fd && prev_pipe_read) {
		if (strcmp(cmd[0], "cd") == 0) {
			if (cmd[1] == NULL || cmd[2] != NULL)
				ft_putstr_fd("error: cd: bad arguments\n", 2)
			else if (chdir(cmd[1]) != 0) {
				ft_putstr_fd("error: cd: cannot change directory to ", 2);
				ft_putstr_fd(cmd[1], 2);
				ft_putstr_fd("\n", 2);
			}
		}
		else {
			pid_t	pid = fork();
			if (pid == -1)
				fatal_err();
			if (pid == CHILD) {
				if (*prev_pipe_read != -1)
					dup2(*prev_pipe_read, STDIN_FILENO);
				if (pipe_fd[WRITE] != -1)
					dup2(pipe_fd[WRITE], STDOUT_FILENO);
				if (execve(cmd[0], cmd, env) == -1) {
					ft_putstr_fd("error: cannot execute ", 2);
					ft_putstr_fd(cmd[0], 2);
					ft_putstr_fd("\n", 2);
				}
				exit(0);
			}
			else {
				waitpid(pid, NULL, 0);
				if (*prev_pipe_read != -1) {
					close(*prev_pipe_read);
					*prev_pipe_read = -1;
				}
				if (pipe_fd[WRITE] != -1) {
					close(pipe_fd[WRITE]);
					pipe_fd[WRITE] = -1;
				}
				if (pipe_fd[READ] != -1) {
					*prev_pipe_read = pipe_fd[READ];
					pipe_fd[READ] = -1;
				}
			}
		}
	}
}

int	main(int argc, char **argv, char **env) {
	if (argc > 1) {
		int	start = 1;
		int	pipe_fd[2] = {-1, -1};
		int	prev_pipe_read = -1;

		for (int i = 1; argv[i]; i++) {
			if (strcmp(argv[i], "|") == 0 || strcmp(argv[i], ";") == 0) {
				if (strcmp(argv[i], "|") == 0) {
					if (pipe(pipe_fd) == -1)
						fatal_err();
				}
				argv[i] = NULL;
				exec_cmd(&(argv[start]), env, pipe_fd, &prev_pipe_read);
				start = i + 1;
			}
		}
		exec_cmd(&(argv[start]), env, pipe_fd, &prev_pipe_read);
	}
}