ajout des builtins pwd cd et export

README.md

@@ -4,7 +4,7 @@
 	- [get root access using sudo su](https://superuser.com/questions/408990/how-do-i-log-out-of-sudo-su)
 - [what is a tty](https://www.howtogeek.com/428174/what-is-a-tty-on-linux-and-how-to-use-the-tty-command/)
 
-```
+```text
                                  |     BASH       |    MINISHELL   |
                                  -----------------------------------
                                  | print | action | print | action |
@@ -150,7 +150,7 @@ There are three functions to use to get the value of a capability :
 - **ttyname** : `char *ttyname(int fd);` returns a pointer to the null-terminated pathname of the terminal device that is open on the file descriptor fd, or NULL on error (for example, if fd is not connected to a terminal)
 - **ttyslot** : `int ttyslot(void);` returns the index of the current user's entry in some file
 - **ioctl** : `int ioctl(int fd, unsigned long request, ...);` manipulates the underlying device parameters of special files. In particular, many operating characteristics of character special files (e.g., terminals) may be controlled with ioctl() requests. The argument fd must be an open file descriptor
-- **getenv** : `char *getenv(const char *name);` searches the environment list to find the environment variable name, and returns a pointer to the corresponding value string
+- **getenv** : `char *getenv(const char *name);` searches the environment list to find the environment variable name, and returns a pointer to the corresponding value string, or NULL if not found
 - **tcsetattr** : `int tcsetattr(int fd, int optional_actions, const struct termios *termios_p);` tcsetattr() only works in an environment where either a controlling terminal exists, or stdin and stderr refer to tty devices. Specifically, it does not work in a TSO environment. Changes the attributes associated with a terminal. New attributes are specified with a termios control structure. Programs should always issue a tcgetattr() first, modify the desired fields, and then issue a tcsetattr(). tcsetattr() should never be issued using a termios structure that was not obtained using tcgetattr(). tcsetattr() should use only a termios structure that was obtained by tcgetattr()
 - **tcgetattr** : `int tcgetattr(int fildes, struct termios *termptr);` Gets a termios structure, which contains control information for a terminal associated with fildes. It stores that information in a memory location that termptr points to. The contents of a termios structure are described in tcsetattr()