Composer 是PHP中用來管理依賴(dependency)關係的工具。你可以在自己的專案中宣告所依賴的外部工具庫(libraries)，Composer會幫你安裝這些依賴的程式庫檔案。
PHP Composer 安裝
系統需求：
Composer 需要PHP5.3.2 以上的環境來運作。有幾個敏感的PHP設定和編譯標誌也是必需的，但安裝程式會發出警告當存在任何不相容的情況。
例如PHP的擴充功能的要求是，安裝或重新編譯php without –disable-phar
為了從來源位址安裝軟體包，而不是簡單的壓縮檔案包，您將需要安裝軟體包的版本控制工具，如git、svn或hg等。
Composer 是相容多平台的，其運作適用於Windows，Linux和OSX。
安裝失敗的錯誤訊息：
curl -sS https://getcomposer.org/installer | PHP
#!/usr/bin/env php
some settings on your machine make Composer unable to work properly.
Make sure that you fix the issues listed below and run this script again:
The phar extension is missing.
Install it or recompile php without –disable-phar
Your PHP (5.2.9) is too old, you must upgrade to PHP 5.3.2 or higher.
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我的本機預設開發環境是PHP 5.2.9，當我嘗試在PHP 5.2. 9上安裝時，提示版本過低，需要升級到PHP 5.3.2 或更高的版本。
於是我下載XAMPP 1.7.7 usb lite 版本。
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php\php.exe -v
PHP 5.3.8 (cli) (built: Aug 23 2011 11:50:20)
Copyright (c) 1997-2011 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies
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XAMPP 1.7.7 下的PHP環境是5.3.8。確認我的PHP環境大於等於PHP5.3.2後。
PHP 5.3 安裝Composer
E:\USB\Dropbox\phpstorm\php53>curl -sS https://getcomposer.org/installer | E:\USB\xampp_177\php\php.exe
#!/usr/bin/env php
Some settings on your machine may cause stability issues with Composer.
If you encounter issues, try to change the following:
The openssl extension is missing, which will reduce the security and stability o
f Composer.
If possible you should enable it or recompile php with –with-openssl
Downloading…
Composer successfully installed to: E:\USB\Dropbox\phpstorm\php53\composer.phar
Use it: php composer.phar
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注意：
我關閉了XAMPP 1.7.7 Apache的SSL模組，所以Composer提示我警告，為了安全因素建議我開啟SSL模組。不開啟也不影響使用。
安裝時的參數| PHP，一定要改為真實的PHP環境路徑，例如| E:\USB\xampp_177\php\php.exe
使用Composer為PHP路徑指令，在我們安裝的環境中，使用方法為：E:\USB\xampp_177\php/php.exe composer.phar 指令。
我安裝的環境是在Windows下，如果在Linux下，而PHP 5.3 環境也不在預設PHP指令下時，應該採用| /usr/php/53/usr/bin/php，例如：
curl -sS https://getcomposer.org/installer | /usr/php/53/usr/bin/php
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安裝完成後，檢查安裝版本。
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php/php.exe composer.phar -V
Composer version 0209bd31a0ac3aeb2a68fc81e2d03c71072bef33
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檢查PHP Composer指令：
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php/php.exe composer.phar
______
/ ____/___ ____ ___ ____ ____ ________ _____
/ / / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__ ) __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
/_/
Composer version 0209bd31a0ac3aeb2a68fc81e2d03c71072bef33
Usage:
[options] command [arguments]
Options:
–help -h Display this help message.
–quiet -q Do not output any message.
–verbose -v Increase verbosity of messages.
–version -V Display this application version.
–ansi Force ANSI output.
–no-ansi Disable ANSI output.
–no-interaction -n Do not ask any interactive question.
–profile Display timing and memory usage information
–working-dir -d If specified, use the given directory as working directory
.
Available commands:
about Short information about Composer
archive Create an archive of this composer package
config Set config options
create-project Create new project from a package into given directory.
depends Shows which packages depend on the given package
diagnose Diagnoses the system to identify common errors.
dump-autoload Dumps the autoloader
dumpautoload Dumps the autoloader
help Displays help for a command
init Creates a basic composer.json file in current directory.
install Installs the project dependencies from the composer.lock file
if present, or falls back on the composer.json.
list Lists commands
require Adds required packages to your composer.json and installs the
m
run-script Run the scripts defined in composer.json.
search Search for packages
self-update Updates composer.phar to the latest version.
selfupdate Updates composer.phar to the latest version.
show Show information about packages
status Show a list of locally modified packages
update Updates your dependencies to the latest version according to
composer.json, and updates the composer.lock file.
validate Validates a composer.json登入後複製
這樣我們在PHP5.3環境下的Composer已經安裝完成。
類似的方法我們也可以安裝PHP 5.4的環境。
PHP 5.4 安裝 Composer
下載XAMPP 1.8.1 usb lite 版本，將得到PHP5.4.7環境。
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_181\php\php.exe -v
PHP 5.4.7 (cli) (built: Sep 12 2012 23:48:31)
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2012 Zend Technologies
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確定版本高於PHP 5.3.2 後，開始安裝：
##
E:\USB\Dropbox\phpstorm\php54>curl -sS https://getcomposer.org/installer | E:\USB\xampp_181\php\php.exe
#!/usr/bin/env php
Some settings on your machine may cause stability issues with Composer.
If you encounter issues, try to change the following:
The openssl extension is missing, which will reduce the security and stability o
f Composer.
If possible you should enable it or recompile php with –with-openssl
Downloading…
Composer successfully installed to: E:\USB\Dropbox\phpstorm\php54\composer.phar
Use it: php composer.phar
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#安裝完成後，檢查安裝版本。
E:\USB\Dropbox\phpstorm\php54>E:\USB\xampp_181\php/php.exe composer.phar -V
Composer version 0209bd31a0ac3aeb2a68fc81e2d03c71072bef33
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這樣，PHP 5.4 環境下的Composer也安裝成功了。
PHP Composer 使用
這裡我只簡單示範使用PHP Composer安裝Symfony框架。
首先大概講解一下指令的標準格式：
php composer.phar create-project symfony/framework-standard-edition path/ 2.2.1
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第一個參數PHP為本機PHP開發環境，指向PHP執行指令。
第二個參數，為composer.phar方式下載。
第三個參數，為動作指令，例如create-project，目的是為了建立一個新的專案從一個軟體包到指定目錄。
第四個參數，為本機安裝的目錄。
第五個參數，為安裝軟體套件的版本。
根據上述我們在PHP5.4環境下安裝的Composer，我們的安裝指令為：
E:\USB\Dropbox\phpstorm\php54>E:\USB\xampp_181\php/php.exe composer.phar create-project symfony/framework-standard-edition E:\USB\xampp_181\htdocs\Symfony 2.2.1
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安裝結果：
Installing symfony/framework-standard-edition (v2.2.1)
– Installing symfony/framework-standard-edition (v2.2.1)
Downloading: 100%
Created project in E:\USB\xampp_181\htdocs\Symfony
Loading composer repositories with package information
Installing dependencies from lock file
– Installing doctrine/lexer (v1.0)
Downloading: 100%
– Installing doctrine/annotations (v1.1)
Downloading: 100%
– Installing doctrine/cache (v1.0)
Downloading: 100%
– Installing doctrine/collections (v1.1)
Downloading: 100%
– Installing twig/twig (v1.12.2)
Downloading: 100%
– Installing psr/log (1.0.0)
Downloading: 100%
– Installing doctrine/inflector (v1.0)
Downloading: 100%
– Installing doctrine/common (2.4.0-RC1)
Downloading: 100%
– Installing symfony/symfony (v2.2.1)
Downloading: 100%
– Installing jdorn/sql-formatter (v1.2.0)
Downloading: 100%
– Installing doctrine/dbal (2.3.3)
Downloading: 100%
– Installing doctrine/doctrine-bundle (v1.2.0-beta1)
Downloading: 100%
– Installing doctrine/orm (2.3.3)
Downloading: 100%
– Installing jms/cg (1.0.0)
Downloading: 100%
– Installing phpoption/phpoption (1.2.0)
Downloading: 100%
– Installing jms/parser-lib (1.0.0)
Downloading: 100%
– Installing jms/metadata (1.3.0)
Downloading: 100%
– Installing jms/aop-bundle (1.0.0)
Downloading: 100%
– Installing jms/di-extra-bundle (1.3.0)
Downloading: 100%
– Installing jms/security-extra-bundle (1.4.0)
Downloading: 100%
– Installing sensio/distribution-bundle (v2.2.1)
Downloading: 100%
– Installing sensio/framework-extra-bundle (v2.2.1)
Downloading: 100%
– Installing sensio/generator-bundle (v2.2.1)
Downloading: 100%
– Installing kriswallsmith/assetic (v1.1.0-alpha4)
Downloading: 100%
– Installing symfony/assetic-bundle (v2.1.2)
Downloading: 100%
– Installing monolog/monolog (1.4.1)
Downloading: 100%
– Installing symfony/monolog-bundle (v2.2.0)
Downloading: 100%
– Installing swiftmailer/swiftmailer (v4.3.0)
Downloading: 100%
– Installing symfony/swiftmailer-bundle (v2.2.0)
Downloading: 100%
– Installing twig/extensions (v1.0.0)
Downloading: 100%
kriswallsmith/assetic suggests installing leafo/lessphp (Assetic provides the integration with the lessphp LESS compiler)
kriswallsmith/assetic suggests installing leafo/scssphp (Assetic provides the integration with the scssphp SCSS compiler)
kriswallsmith/assetic suggests installing leafo/scssphp-compass (Assetic provides the integration with the SCSS compass plugin)
kriswallsmith/assetic suggests installing ptachoire/cssembed (Assetic provides the integration with phpcssembed to embed data uris)
monolog/monolog suggests installing doctrine/couchdb (Allow sending log messages to a CouchDB server)
monolog/monolog suggests installing ext-amqp (Allow sending log messages to an AMQP server (1.0+ required))
monolog/monolog suggests installing ext-mongo (Allow sending log messages to a MongoDB server)
monolog/monolog suggests installing mlehner/gelf-php (Allow sending log messages to a GrayLog2 server)
monolog/monolog suggests installing raven/raven (Allow sending log messages to a Sentry server)
Generating autoload files
Clearing the cache for the dev environment with debug true
Installing assets using the hard copy option
Installing assets for Symfony\Bundle\FrameworkBundle into web/bundles/framework
Installing assets for Acme\DemoBundle into web/bundles/acmedemo
Installing assets for Sensio\Bundle\DistributionBundle into web/bundles/sensiodistribution
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從命令列結果，我們看到了整個Symfony框架的安裝過程與結果。
PHP Composer 定義依賴關係
Composer在使用時會自動尋找composer.json這個檔案。 composer.json將用來定義整個專案的依賴套件。例如：
{
"require": {
"monolog/monolog": "1.2.*"
}
}登入後複製
依賴套件簡單的說明，我們的專案需要一些從1.2開始的任何版本的monolog/monolog套件。
Composer是PHP中的一個依賴關係管理工具。透過Composer我們可以在發佈軟體時節省大量的文件數目和控制依賴套件的版本。
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