What is the difference between require and require-dev sections in composer.json?

Question

I'm beginning using composer, I know so little about it and have a little experience with web application development.

I just walk through Nettuts+ Tutorial, so I have basic question about composer.

{
  "require": {
    "laravel/framework": "4.0.*",
    "way/generators": "dev-master",
    "twitter/bootstrap": "dev-master",
    "conarwelsh/mustache-l4": "dev-master"
  },
  "require-dev": {
    "phpunit/phpunit": "3.7.*",
    "mockery/mockery": "0.7.*"
  },
  "autoload": {
    "classmap": [
      "app/commands",
      "app/controllers",
      "app/models",
      "app/database/migrations",
      "app/database/seeds",
      "app/tests/TestCase.php"
    ]
  },
  "scripts": {
    "post-update-cmd": "php artisan optimize"
  },
  "minimum-stability": "dev"
}

1. Whatever appears in "require-dev" part, will only be downloaded and installed with composer install --dev?
2. I read some of composer's documentation but still don't understand what is the reason we have "require-dev" part? Is it because of we want to get specific version of the package rather always getting the latest stable version?

Answer 1

Different Environments

Typically, software will run in different environments:

• development
• testing
• staging
• production

Different Dependencies in Different Environments

The dependencies which are declared in the require section of composer.json are typically dependencies which are required for running an application or a package in

• staging
• production

environments, whereas the dependencies declared in the require-dev section are typically dependencies which are required in

• developing
• testing

environments.

For example, in addition to the packages used for actually running an application, packages might be needed for developing the software, such as:

• friendsofphp/php-cs-fixer (to detect and fix coding style issues)
• squizlabs/php_codesniffer (to detect and fix coding style issues)
• phpunit/phpunit (to drive the development using tests)
• etc.

Deployment

Now, in development and testing environments, you would typically run

$ composer install

to install both production and development dependencies.

However, in staging and production environments, you only want to install dependencies which are required for running the application, and as part of the deployment process, you would typically run

$ composer install --no-dev

to install only production dependencies.

Semantics

In other words, the sections

• require
• require-dev

indicate to composer which packages should be installed when you run

$ composer install

or

$ composer install --no-dev

That is all.

Note Development dependencies of packages your application or package depend on will never be installed

For reference, see:

• https://getcomposer.org/doc/04-schema.md#require
• https://getcomposer.org/doc/04-schema.md#require-dev