To control the priority of Composer multi-repository packages in PHP projects, simply arrange the order of repository as needed in composer.json. First, list the repositories in the repositories array by priority, and Composer will look for packages in this order; second, if you want a private repository to take priority over Packagist, put it at the top of the list; in addition, you can use the path repository to achieve local override, which is suitable for the development and testing stage; finally, be careful to avoid conflicts caused by packages of the same name in different repositories. It is recommended to use a unique naming prefix and use the composershow command to check the source.

Packagist is Composer's default package repository for centralized management and discovery of PHP packages. It stores the metadata of the package instead of the code itself, allowing developers to define dependencies through composer.json and get the code from the source (such as GitHub) at installation time. Its core functions include: 1. Provide centralized package browsing and search; 2. Manage versions to meet dependency constraints; 3. Automatic updates are achieved through webhooks. While custom repositories can be configured to use Composer, Packagist simplifies the distribution process of public packages. The publishing package needs to be submitted to Packagist and set up a webhook, so that others can install it with one click through composerrequire.

Managing environment configuration in PHP projects can be achieved in a variety of ways. First, use the .env file of the Dotenv library to create configuration files for different environments such as .env.development and .env.production, and load them through vlucas/phpdotenv, and submit the sample files and ignore the real files; second, store non-sensitive metadata in the extra part of composer.json, such as cache time and log levels for script reading; third, maintain independent configuration files such as config/development.php for different environments, and load the corresponding files according to the APP_ENV variable at runtime; finally, use CI/C

To quickly get detailed information about a specific package in Composer, use the composershowvendor/package command. For example, composershowmonolog/monolog, which will display version, description, dependencies and other information; if you are not sure of the name, you can use some names to combine --platform to view platform requirements; add --name-only to simplify output; use -v to display more detailed content; support wildcard search, such as monolog/*.

PHP's automatic loading methods include PSR-0, PSR-4, classmap and files. The core purpose is to implement automatic loading of classes without manually introducing files. 1. PSR-0 is an early standard, and automatically loads through class name and file path mapping, but because the naming specifications are strict and the support for underscores as directory separators have been rarely used; 2. PSR-4 is a modern standard, which adopts a more concise namespace and directory mapping method, allowing a namespace to correspond to multiple directories and does not support underscore separation, becoming the mainstream choice; 3. classmap generates a static mapping table of class names and paths by scanning the specified directory, which is suitable for legacy code that does not follow the PSR specification, but new files need to be regenerated and large directories

To use Composer to set up automatic loading of PHP projects, you must first edit the composer.json file and select the appropriate automatic loading method. If the most commonly used PSR-4 standard is adopted, the mapping of namespace and directory can be defined in the psr-4 field of autoload, such as mapping MyApp\ to src/directory, so that the MyApp\Controllers\HomeController class will automatically load from src/Controllers/HomeController.php; 1. After the configuration is completed, run composerdumpautoload to generate an automatic loading file; 2. If you need to be compatible with old code, you can use it.

Installing Composer takes only a few steps and is suitable for Windows, macOS, and Linux. Windows users should download Composer-Setup.exe and run it to ensure that PHP is installed or XAMPP is used; macOS users need to execute download, verification, and global installation commands through the terminal; Linux users operate similarly to macOS, and then use the corresponding package manager to install PHP and download and move the Composer file to the global directory.

ComposerpluginsextendComposer’sfunctionalitywithoutalteringitscore.Theyautomatetasks,enforcerules,orintegratewithtoolsbyhookingintoComposer'seventsandAPIs.Commonusesincluderunningcustomscripts,modifyingpackagebehavior,andintegratingchecks.Toinstall:1