What are the differences between composer update and composer install?

问题

What are the differences between composer update and composer install?

回答1:

composer update

composer update will update your depencencies as they are specified in composer.json

For example, if you require this package as a dependency:

"mockery/mockery": "0.9.*",

and you have actually installed the 0.9.1 version of the package, running composer update will cause an upgrade of this package (for example to 0.9.2, if it's already been released)

in detail composer update will:

• Read composer.json
• Remove installed packages that are no more required in composer.json
• Check the availability of the latest versions of your required packages
• Install the latest versions of your packages
• Update composer.lock to store the installed packages version

composer install

composer install will not update anything; it will just install all the dependencies as specified in the composer.lock file

In detail:

• Check if composer.lock file exists (if not, run composer-update and create it)
• Read composer.lock file
• Install the packages specified in the composer.lock file

When to install and when to update

• composer update is mostly used in the 'development phase', to upgrade our project packages according to what we have specified in the composer.json file,

• composer install is primarily used in the 'deploying phase' to install our application on a production server or on a testing environment, using the same dependencies stored in the composer.lock file created by composer update.

回答2:

When you run composer install it will look for a lock file and install whatever is contained in it, if it can't find one, it'll read composer.json, install its dependencies and generate a lockfile.

When you run composer update it simply reads composer.json, installs the dependencies and updates the lockfile (or creates a new lockfile).

回答3:

composer install

1. If composer.lock does exist.
   • Processes and installs dependencies from the composer.lock file.
2. If composer.lock does not exist.
   • Process package installs from composer.json.
   • Creates the composer.lock file based on the installed packages.

As per: composer help install:

The install command reads the composer.lock file from the current directory, processes it, and downloads and installs all the libraries and dependencies outlined in that file. If the file does not exist it will look for composer.json and do the same.

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composer update

1. Processes dependencies from the composer.json file (installs, updates and removes).
2. Creates or updates the composer.lock file according to the changes.

As per: composer help update:

The update command reads the composer.json file from the current directory, processes it, and updates, removes or installs all the dependencies.

---

See also: Composer: It’s All About the Lock File

回答4:

The best difference between composer update and composer install

composer install

To add dependencies you need to add it manually to the composer.json file.

If composer.lock file exists, install exactly what's specificated on this file

• Otherwise read composer.json file to look out what dependencies needs to be installed
• Write the composer.lock with the information of the project (installed dependencies)

Not any component will be updated with this command.

composer update

To add or remove dependencies you need to add it manually to the composer.json file

• The composer.lock file will be ignored
• composer.json file dependencies will be installed and updated (if a dependency is not installed it will be downloaded)

If you can't (or don't know how to add or remove a library which is in fact easy,just add the name of the dependency and version in the require property of the file) modify the composer.json file manually or you prefer use the command line instead, composer has special functions for this :

composer require

For example if we want to add a dependency with the command line we will simply execute

composer require twig/twig

• composer.json file will be modified automatically and the new dependency will be added
• the dependency will be downloaded to the project

composer remove

If you want to remove an unused dependency we will execute simply :

composer remove twig/twig --update-with-dependencies

• Twig will be removed with all his dependencies

来源：https://stackoverflow.com/questions/33052195/what-are-the-differences-between-composer-update-and-composer-install