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March 10, 2025 22:06
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Composer Cheatsheet

A comprehensive cheat sheet for Composer, the dependency manager for PHP. Covers installation, dependency management, autoloading, and common commands with examples.

Installation & Basic Usage

Installation

Local Installation:

Download composer.phar and place it in your project directory.

Global Installation:

curl -sS https://getcomposer.org/installer | php
mv composer.phar /usr/local/bin/composer
chmod +x /usr/local/bin/composer

Verify Installation:

composer --version

Ensure that PHP is installed and accessible from your command line.

Basic Commands

composer init

Initializes a new composer project in the current directory.

composer install

Installs the project’s dependencies from the composer.lock file, or composer.json if composer.lock doesn’t exist.

composer update

Updates the project’s dependencies to the latest versions specified in composer.json and updates the composer.lock file.

composer require <package>

Adds a new dependency to the composer.json file and installs it.

composer remove <package>

Removes a dependency from the composer.json file and uninstalls it.

composer dump-autoload

Regenerates the autoloader files.

composer.json Structure 

{
  "name": "vendor/package-name",
  "description": "A short description of the package.",
  "type": "project",
  "license": "MIT",
  "require": {
    "php": ">=7.4",
    "vendor/dependency": "^1.0"
  },
  "autoload": {
    "psr-4": {
      "Namespace\\": "src/"
    }
  },
  "require-dev": {
    "phpunit/phpunit": "^9.0"
  },
  "scripts": {
    "test": "phpunit"
  }
}

Dependency Management

Specifying Versions

1.2.3

Specific version.

>=1.2.3

Minimum version, allows later versions.

<1.2.3

Maximum version, allows earlier versions.

~1.2.3

Equivalent to >=1.2.3 <1.3.0. Allows updates up to the next minor version.

^1.2.3

Equivalent to >=1.2.3 <2.0.0. Allows updates until the next major version.

*

Any version. Not recommended for production.

dev-master

Install the latest code from the master branch. Unstable.

Updating Dependencies

composer update updates your dependencies to the latest versions according to the constraints specified in your composer.json file.

Always commit your composer.lock file after updating dependencies.

If you want to update only single package use composer update vendor/package

Resolving Conflicts

If Composer encounters conflicts, it will provide error messages suggesting how to resolve them. This often involves relaxing version constraints in your composer.json file.

Use composer diagnose to identify common configuration issues.

Consider using the composer prohibits <package> <version> command to understand why a package cannot be installed.

Autoloading

PSR-4 Autoloading

PSR-4 is the recommended autoloading standard.

Specify the namespace to directory mapping in the autoload section of composer.json:

"autoload": {
  "psr-4": {
    "MyProject\\": "src/"
  }
}

This maps the MyProject namespace to the src directory.

After modifying the autoload section, run composer dump-autoload to regenerate the autoloader.

Classmap Autoloading

Classmap autoloading scans specified directories for PHP classes and builds a map.

"autoload": {
  "classmap": [
    "src/",
    "lib/"
  ]
}

Run composer dump-autoload after modifying the classmap section.

Files Autoloading

Files autoloading includes specified PHP files.

"autoload": {
  "files": [
    "src/helpers.php",
    "lib/config.php"
  ]
}

Run composer dump-autoload after modifying the files section.

Optimizing Autoloading

Use the -o or --optimize option with composer dump-autoload to generate an optimized autoloader for production:

composer dump-autoload -o

This generates a single autoload_static.php file which can improve performance.

Advanced Usage

Scripts

Define custom scripts in the scripts section of composer.json:

"scripts": {
  "test": "phpunit",
  "lint": "phpcs --standard=PSR12 src/"
}

Run scripts using composer <script-name>:

composer test
composer lint

Repositories

Configure custom repositories in the repositories section of composer.json to include packages from alternative sources:

"repositories": [
  {
    "type": "vcs",
    "url": "https://github.com/my-org/private-repo"
  }
]

Supported repository types include vcs (version control system), package, composer, and path.

Platform Configuration

Specify platform requirements in the config section of composer.json to override the detected environment:

"config": {
  "platform": {
    "php": "7.4",
    "ext-intl": "7.4"
  }
}

This is useful for ensuring compatibility on different environments.

Plugins

Composer plugins extend Composer’s functionality. Install plugins like any other dependency.

Ensure composer/installers is required in your project to handle different package types:

composer require composer/installers