Enable / Disable Auditing From PHP

In PL/SQL Plus, i can enable/disable auditing when i connect as sysdba by using these command:

SQL> ALTER SYSTEM SET audit_trail=db SCOPE=SPFILE
SQL> shutdown
SQL> startup

I've done it successfully with PL/SQL Plus command line. But in PHP, how can i do that?How to execute "shutdown" and "startup" from PHP?
I've found this code for connect to oracle as sysdba:

oci_connect("/", "", null, null, OCI_SYSDBA);

From the following link:

[URL]......

But, i still can't execute "shutdown", "startup";