What is a script?

A script, in Composer's terms, can either be a PHP callback (defined as a static method) or any command-line executable command. Scripts are useful for executing a package's custom code or package-specific commands during the Composer execution process.

NOTE: Only scripts defined in the root package's composer.json are executed. If a dependency of the root package specifies its own scripts, Composer does not execute those additional scripts.

Event names

Composer fires the following named events during its execution process:

NOTE: Composer makes no assumptions about the state of your dependencies prior to install or update. Therefore, you should not specify scripts that require Composer-managed dependencies in the pre-update-cmd or pre-install-cmd event hooks. If you need to execute scripts prior to install or update please make sure they are self-contained within your root package.

Defining scripts

The root JSON object in composer.json should have a property called "scripts", which contains pairs of named events and each event's corresponding scripts. An event's scripts can be defined as either as a string (only for a single script) or an array (for single or multiple scripts.)

For any given event:

Script definition example:

    "scripts": {
        "post-update-cmd": "MyVendor\\MyClass::postUpdate",
        "post-package-install": [
        "post-install-cmd": [
            "phpunit -c app/"

Using the previous definition example, here's the class MyVendor\MyClass that might be used to execute the PHP callbacks:


namespace MyVendor;

use Composer\Script\Event;

class MyClass
    public static function postUpdate(Event $event)
        $composer = $event->getComposer();
        // do stuff

    public static function postPackageInstall(Event $event)
        $installedPackage = $event->getOperation()->getPackage();
        // do stuff

    public static function warmCache(Event $event)
        // make cache toasty

When an event is fired, Composer's internal event handler receives a Composer\Script\Event object, which is passed as the first argument to your PHP callback. This Event object has getters for other contextual objects:

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