How To Define Global Constant in CodeIgniter 4 Tutorial

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Inside this article we will see the concept to define global constant in codeigniter 4. Global constant simply means variables which we can access anywhere inside application at any point. Value for constants is fixed for lifetime. We can’t alter values for those.

List of all available global constants in CodeIgniter 4, Click here for article.

Here we will discuss to create global constant step by step and how to use in codeigniter 4 application.

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Let’s get started.

CodeIgniter 4 Installation

To create a CodeIgniter 4 setup run this given command into your shell or terminal. Please make sure composer should be installed.

composer create-project codeigniter4/appstarter codeigniter-4

Assuming you have successfully installed application into your local system.

Environment (.env) Setup

When we install CodeIgniter 4, we will have env file at root. To use the environment variables means using variables at global scope we need to do env to .env

Either we can do via renaming file as simple as that. Also we can do by terminal command.

Open project in terminal

cp env .env

Above command will create a copy of env file to .env file. Now we are ready to use environment variables.

Enable Development Mode

CodeIgniter starts up in production mode by default. You need to make it in development mode to see any error if you are working with application.

Open .env file from root.

# CI_ENVIRONMENT = production

 // Do it to 
CI_ENVIRONMENT = development

Now application is in development mode.

What is a Global Constant?

Global constants are also termed as core constants of application. It simply means theses –

  • Variables which can accessed through out application means globally available to use.
  • Values of constants can’t be altered upto it’s lifetime.
  • We can define constant using PHP function define()

Define Global Constant in Application

Global constants can be define in two ways inside Codeigniter 4 application. These are the following ways –

  • By using .env file
  • By using Constants.php file

Global Constant using .env (environment) file

Open .env file from application root. To define global constants, simply define like this

MY_CONSTANT="This is a global constant defined in .env file"

How To Use?

To call inside application files, use getenv() function of codeigniter 4.

<?php echo getenv('MY_CONSTANT') ?>


<?= getenv('MY_CONSTANT') ?>


<?= env('MY_CONSTANT') ?>

Global Constant Using Constants.php File

Open Constants.php file from /app/Config folder. Here, to define global constants we use php function define()

Add this line at footer of file –

defined('MY_CONSTANT') || define('MY_CONSTANT', 'This is a global constant defined in Constants.php file');  

defined(‘MY_CONSTANT’) It is checking first that constant is already exists or not. If not then using define() it is creating.

How To Use?

To call inside application files, use like this.

<?php echo MY_CONSTANT; ?>



We hope this article helped you to learn about How To Define Global Constant in CodeIgniter 4 Tutorial in a very detailed way.

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Sanjay KumarHello friends, I am Sanjay Kumar a Web Developer by profession. Additionally I'm also a Blogger, Youtuber by Passion. I founded Online Web Tutor and Skillshike platforms. By using these platforms I am sharing the valuable knowledge of Programming, Tips and Tricks, Programming Standards and more what I have with you all. Read more