- Introduction
- composer.json: Project setup
- Installing dependencies
- Updating dependencies to their latest versions
- Packagist
- Platform packages
- Autoloading
Basic usage#
Introduction#
For our basic usage introduction, we will be installing monolog/monolog
,
a logging library. If you have not yet installed Composer, refer to the
Intro chapter.
Note: for the sake of simplicity, this introduction will assume you have performed a local install of Composer.
composer.json
: Project setup#
To start using Composer in your project, all you need is a composer.json
file. This file describes the dependencies of your project and may contain
other metadata as well. It typically should go in the top-most directory of
your project/VCS repository. You can technically run Composer anywhere but
if you want to publish a package to Packagist.org, it will have to be able
to find the file at the top of your VCS repository.
The require
key#
The first thing you specify in composer.json
is the
require
key. You are telling Composer which
packages your project depends on.
{
"require": {
"monolog/monolog": "2.0.*"
}
}
As you can see, require
takes an object that maps
package names (e.g. monolog/monolog
) to version constraints (e.g.
1.0.*
).
Composer uses this information to search for the right set of files in package
"repositories" that you register using the repositories
key, or in Packagist.org, the default package repository.
In the above example, since no other repository has been registered in the
composer.json
file, it is assumed that the monolog/monolog
package is registered
on Packagist.org. (Read more about Packagist, and
about repositories).
Package names#
The package name consists of a vendor name and the project's name. Often these
will be identical - the vendor name only exists to prevent naming clashes. For
example, it would allow two different people to create a library named json
.
One might be named igorw/json
while the other might be seldaek/json
.
Read more about publishing packages and package naming. (Note that you can also specify "platform packages" as dependencies, allowing you to require certain versions of server software. See platform packages below.)
Package version constraints#
In our example, we are requesting the Monolog package with the version constraint
2.0.*
.
This means any version in the 2.0
development branch, or any version that is
greater than or equal to 2.0 and less than 2.1 (>=2.0 <2.1
).
Please read versions for more in-depth information on versions, how versions relate to each other, and on version constraints.
How does Composer download the right files? When you specify a dependency in
composer.json
, Composer first takes the name of the package that you have requested and searches for it in any repositories that you have registered using therepositories
key. If you have not registered any extra repositories, or it does not find a package with that name in the repositories you have specified, it falls back to Packagist.org (more below).When Composer finds the right package, either in Packagist.org or in a repo you have specified, it then uses the versioning features of the package's VCS (i.e., branches and tags) to attempt to find the best match for the version constraint you have specified. Be sure to read about versions and package resolution in the versions article.
Note: If you are trying to require a package but Composer throws an error regarding package stability, the version you have specified may not meet your default minimum stability requirements. By default, only stable releases are taken into consideration when searching for valid package versions in your VCS.
You might run into this if you are trying to require dev, alpha, beta, or RC versions of a package. Read more about stability flags and the
minimum-stability
key on the schema page.
Installing dependencies#
To initially install the defined dependencies for your project, you should run the
update
command.
php composer.phar update
This will make Composer do two things:
- It resolves all dependencies listed in your
composer.json
file and writes all of the packages and their exact versions to thecomposer.lock
file, locking the project to those specific versions. You should commit thecomposer.lock
file to your project repo so that all people working on the project are locked to the same versions of dependencies (more below). This is the main role of theupdate
command. - It then implicitly runs the
install
command. This will download the dependencies' files into thevendor
directory in your project. (Thevendor
directory is the conventional location for all third-party code in a project). In our example from above, you would end up with the Monolog source files invendor/monolog/monolog/
. As Monolog has a dependency onpsr/log
, that package's files can also be found insidevendor/
.
Tip: If you are using git for your project, you probably want to add
vendor
in your.gitignore
. You really don't want to add all of that third-party code to your versioned repository.
Commit your composer.lock
file to version control#
Committing this file to version control is important because it will cause anyone
who sets up the project to use the exact same
versions of the dependencies that you are using. Your CI server, production
machines, other developers in your team, everything and everyone runs on the
same dependencies, which mitigates the potential for bugs affecting only some
parts of the deployments. Even if you develop alone, in six months when
reinstalling the project you can feel confident that the dependencies installed are
still working, even if the dependencies have released many new versions since then.
(See note below about using the update
command.)
Note: For libraries it is not necessary to commit the lock file, see also: Libraries - Lock file.
Installing from composer.lock
#
If there is already a composer.lock
file in the project folder, it means either
you ran the update
command before, or someone else on the project ran the update
command and committed the composer.lock
file to the project (which is good).
Either way, running install
when a composer.lock
file is present resolves and installs
all dependencies that you listed in composer.json
, but Composer uses the exact versions listed
in composer.lock
to ensure that the package versions are consistent for everyone
working on your project. As a result you will have all dependencies requested by your
composer.json
file, but they may not all be at the very latest available versions
(some of the dependencies listed in the composer.lock
file may have released newer versions since
the file was created). This is by design, ensuring that your project does not break because of
unexpected changes in dependencies.
So after fetching new changes from your VCS repository it is recommended to run
a Composer install
to make sure the vendor directory is up in sync with your
composer.lock
file.
php composer.phar install
Composer enables reproducible builds by default. This means that running the
same command multiple times will produce a vendor/
directory containing files
that are identical (except their timestamps), including the autoloader files.
It is especially beneficial for environments that require strict
verification processes, as well as for Linux distributions aiming to package PHP
applications in a secure and predictable manner.
Updating dependencies to their latest versions#
As mentioned above, the composer.lock
file prevents you from automatically getting
the latest versions of your dependencies. To update to the latest versions, use the
update
command. This will fetch the latest matching
versions (according to your composer.json
file) and update the lock file
with the new versions.
php composer.phar update
Note: Composer will display a Warning when executing an
install
command if thecomposer.lock
has not been updated since changes were made to thecomposer.json
that might affect dependency resolution.
If you only want to install, upgrade or remove one dependency, you can explicitly list it as an argument:
php composer.phar update monolog/monolog [...]
Packagist#
Packagist.org is the main Composer repository. A Composer
repository is basically a package source: a place where you can get packages
from. Packagist aims to be the central repository that everybody uses. This
means that you can automatically require
any package that is available there,
without further specifying where Composer should look for the package.
If you go to the Packagist.org website, you can browse and search for packages.
Any open source project using Composer is recommended to publish their packages on Packagist. A library does not need to be on Packagist to be used by Composer, but it enables discovery and adoption by other developers more quickly.
Platform packages#
Composer has platform packages, which are virtual packages for things that are installed on the system but are not actually installable by Composer. This includes PHP itself, PHP extensions and some system libraries.
-
php
represents the PHP version of the user, allowing you to apply constraints, e.g.^7.1
. To require a 64bit version of php, you can require thephp-64bit
package. -
hhvm
represents the version of the HHVM runtime and allows you to apply a constraint, e.g.,^2.3
. -
ext-<name>
allows you to require PHP extensions (includes core extensions). Versioning can be quite inconsistent here, so it's often a good idea to set the constraint to*
. An example of an extension package name isext-gd
. -
lib-<name>
allows constraints to be made on versions of libraries used by PHP. The following are available:curl
,iconv
,icu
,libxml
,openssl
,pcre
,uuid
,xsl
.
You can use show --platform
to get a list of your locally
available platform packages.
Autoloading#
For libraries that specify autoload information, Composer generates a
vendor/autoload.php
file. You can include this file and start
using the classes that those libraries provide without any extra work:
require __DIR__ . '/vendor/autoload.php';
$log = new Monolog\Logger('name');
$log->pushHandler(new Monolog\Handler\StreamHandler('app.log', Monolog\Logger::WARNING));
$log->warning('Foo');
You can even add your own code to the autoloader by adding an
autoload
field to composer.json
.
{
"autoload": {
"psr-4": {"Acme\\": "src/"}
}
}
Composer will register a PSR-4 autoloader
for the Acme
namespace.
You define a mapping from namespaces to directories. The src
directory would
be in your project root, on the same level as the vendor
directory. An example
filename would be src/Foo.php
containing an Acme\Foo
class.
After adding the autoload
field, you have to re-run
this command:
php composer.phar dump-autoload
This command will re-generate the vendor/autoload.php
file.
See the dump-autoload
section for
more information.
Including that file will also return the autoloader instance, so you can store the return value of the include call in a variable and add more namespaces. This can be useful for autoloading classes in a test suite, for example.
$loader = require __DIR__ . '/vendor/autoload.php';
$loader->addPsr4('Acme\\Test\\', __DIR__);
In addition to PSR-4 autoloading, Composer also supports PSR-0, classmap and
files autoloading. See the autoload
reference for
more information.
See also the docs on optimizing the autoloader.
Note: Composer provides its own autoloader. If you don't want to use that one, you can include
vendor/composer/autoload_*.php
files, which return associative arrays allowing you to configure your own autoloader.
Found a typo? Something is wrong in this documentation? Fork and edit it!