Assignment name  : ft_popen
Expected files   : ft_popen.c
Allowed functions: pipe, fork, dup2, execvp, close, exit
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Write the following function:

int ft_popen(const char *file, char *const argv[], char type);

The function must launch the executable file with the arguments argv (using execvp).
If type is 'r' the function must return a file descriptor connected to the output of the command.
If type is 'w' the function must return a file descriptor connected to the input of the command.
In case of error or invalid parameter the function must return -1.

For example, the function could be used like that:

int main()
{
    int  fd;
    char *line;

    fd = ft_popen("ls", (char *const []){"ls", NULL}, 'r');
    while ((line = get_next_line(fd)))
        ft_putstr(line);
    return (0);
}


int	main() {
	int	fd = ft_popen("ls", (char *const []){"ls", NULL}, 'r');
	dup2(fd, 0);
	fd = ft_popen("grep", (char *const []){"grep", "c", NULL}, 'r');
	char	*line;
	while ((line = get_next_line(fd)))
		printf("%s", line);
}


Hints:
Do not leak file descriptors!
This exercise is inspired by the libc's popen().