database configuration not work

i have tried many time my database does not connected THIS ERROR HAVE COME I ALSO MY DATABASE .PHP file also i add datebase.php file attache for you to check the problem also i add new in model/property.php file i also another method on controller/properties.php file on this file i add db_test method 
and this is the link when i connect to the database 
http://localhost:8888/index.php/properties/db_test
and last thing 
this command when i run in terminal 
env DB_USER=root DB_PASSWD=root  DB_NAME=ci_course php -S localhost:8888
but not work please help to solve the issue 
A PHP Error was encountered
Severity: Warning
Message: mysqli::real_connect(): (HY000/2002): No such file or directory
Filename: mysqli/mysqli_driver.php
Line Number: 202
Backtrace:
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/application/models/Property.php
Line: 17
Function: database
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/application/controllers/Properties.php
Line: 29
Function: connection_test
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/index.php
Line: 315
Function: require_once
A PHP Error was encountered
Severity: Warning
Message: Cannot modify header information - headers already sent by (output started at /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/system/core/Exceptions.php:272)
Filename: core/Common.php
Line Number: 573
Backtrace:
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/application/models/Property.php
Line: 17
Function: database
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/application/controllers/Properties.php
Line: 29
Function: connection_test
File: /Applications/file/Ex_Files_CodeIgniter_Basics/Ch01/01_06_final/index.php
Line: 315
Function: require_once
A Database Error Occurred
Unable to connect to your database server using the provided settings.
Filename: controllers/Properties.php
Line Number: 29

Attached Files

  database.php (Size: 4.45 KB / Downloads: 2)
  Property.php (Size: 287 bytes / Downloads: 1)
  Properties.php (Size: 765 bytes / Downloads: 1)