Composer Update vs. Composer Install: When Should You Use Which?

Understanding the Differences Between 'composer update' and 'composer install'

In the world of PHP development, understanding the intricacies of dependency management is crucial. Among the commonly used tools is Composer, which plays a vital role in managing PHP libraries. This article aims to shed light on the variations between two key Composer commands: 'composer update' and 'composer install.'

'composer update': Upgrading Dependencies

'composer update' caters to the specific task of updating your project's dependencies as outlined in the composer.json file. Consider a scenario where you have specified a dependency like this:

"mockery/mockery": "0.9.*"

Presumably, you have installed version 0.9.1 of this package. Running 'composer update' would initiate an upgrade of the package (e.g., to version 0.9.2) if a newer release exists.

The underlying process of 'composer update' is methodical:

1. Parsing composer.json
2. Removing superfluous installed packages
3. Verifying the latest version availability of required packages
4. Installing the most recent package versions
5. Updating composer.lock to reflect the installed versions

'composer install': Locked-In Dependencies

In contrast, 'composer install' is solely focused on installing dependencies as defined in the composer.lock file. It doesn't engage in any updates. Its workflow consists of:

1. Verifying the existence of composer.lock (initiating 'composer update' from scratch if needed)
2. Parsing composer.lock
3. Installing the packages specified in composer.lock

Choosing Between 'composer update' and 'composer install'

When to employ either command becomes clear based on their distinct functions:

• 'composer update' finds its place during the development phase, enabling you to upgrade dependencies according to composer.json specifications.
• 'composer install' is best suited for the deployment phase, ensuring consistent dependency installation on production or testing environments, guided by the composer.lock file created through 'composer update.'

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