Installing Composer

Composer is the de facto dependency manager for PHP. It takes the pain out of managing third-party libraries — whether you're working with Symfony, Laravel, PHPUnit, Guzzle, or any of the thousands of packages available on Packagist. If you're building a modern PHP application, Composer is non-negotiable.

Prerequisites

1. Connect to your server via SSH (PuTTY on Windows, or your terminal on Linux/macOS).
2. Make sure PHP is installed and up to date (version 7.2.5 or higher):

   php -v

3. Install curl and git if they aren't already present:

   sudo apt update
   sudo apt install curl git -y   # Ubuntu/Debian
   # or
   sudo yum install curl git -y   # CentOS/Rocky/AlmaLinux

Installation

1. Navigate to a directory on your system's PATH — /usr/local/bin is a solid choice:

   cd /usr/local/bin

2. Download and run the Composer installer in one go:

   sudo curl -sS https://getcomposer.org/installer | php

If curl isn't cooperating, you can do this the manual way:

   sudo php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
   sudo php composer-setup.php
   sudo rm composer-setup.php

3. Rename the file and make it executable so you can call it from anywhere:

   sudo mv composer.phar composer
   sudo chmod +x composer

Getting started with a project

1. Head to your project root:

   cd /var/www/my-project

2. Scaffold a new composer.json by running the interactive initializer:

   composer init

3. Install all declared dependencies:

   composer install

4. Pull in a package — here's an example with the Guzzle HTTP client:

   composer require guzzlehttp/guzzle

5. Upgrade everything to the latest compatible versions:

   composer update

Handy commands to know

What you want to do	Command
List installed packages	composer show
Update a single package	composer update vendor/package
Remove a package	composer remove vendor/package
Clear the cache	composer clear-cache
Install without cache (great for debugging)	composer install --no-cache