For CodeIgniter 4, a good approach is to compare your project’s app/Config/ files against the corresponding files shipped in vendor/codeigniter4/framework/app/Config/.

Compare a single file on Linux

diff -u app/Config/App.php vendor/codeigniter4/framework/app/Config/App.php

The -u option produces a readable unified diff. Lines beginning with - are from your project and lines beginning with + are from the new framework version.

Compare the entire configuration directory

diff -ru app/Config vendor/codeigniter4/framework/app/Config

I prefer comparing individual files during an upgrade because it’s easier to distinguish your custom configuration from new CodeIgniter defaults:

diff -u app/Config/App.php vendor/codeigniter4/framework/app/Config/App.php
diff -u app/Config/Database.php vendor/codeigniter4/framework/app/Config/Database.php
diff -u app/Config/Filters.php vendor/codeigniter4/framework/app/Config/Filters.php
diff -u app/Config/Security.php vendor/codeigniter4/framework/app/Config/Security.php

Using Git

Git also has a useful diff viewer even when the files aren’t versions of the same tracked file:

git diff --no-index \
    app/Config/App.php \
    vendor/codeigniter4/framework/app/Config/App.php

This can provide syntax highlighting in terminals that support it.

On Windows

If you’re developing on Windows, WinMerge is particularly convenient. Compare these directories:

your-project\app\Config
your-project\vendor\codeigniter4\framework\app\Config

Other good GUI choices are VS Code’s file comparison and Beyond Compare.

Using VS Code

Right-click your project’s file:

app/Config/App.php

Choose Select for Compare, then right-click:

vendor/codeigniter4/framework/app/Config/App.php

and choose Compare with Selected.

Important caveat

Don’t try to make your app/Config/App.php identical to the framework version. Your file is expected to contain application-specific settings.

For example, if your existing file contains:

public string $indexPage = '';

while the new framework file has:

public string $indexPage = 'index.php';

that doesn’t mean you should change yours.

During an upgrade, you’re primarily looking for:

• New configuration properties
• Removed properties
• Changed property types
• Changed defaults
• Structural changes introduced by CodeIgniter

Keep your application’s intentional customizations.

Don’t forget spark and public/index.php

These files belong to the CodeIgniter project skeleton rather than just the Composer package, so Composer does not necessarily replace your project copies automatically.

diff spark vendor/codeigniter4/framework/spark
diff public/index.php vendor/codeigniter4/framework/public/index.php

If you haven’t customized them, you can replace them:

cp vendor/codeigniter4/framework/spark spark
cp vendor/codeigniter4/framework/public/index.php public/index.php