¿Qué es Composer?

Composer es una herramienta para la administración de dependencias en PHP. Te permite declarar las bibliotecas de las que depende tu proyecto y las administrará (lnstall / update).

Paso 1, instalar curl

sudo apt install curl

Paso 2, instalar php

sudo apt install php7.2-cli

Paso 3, instalar Composer

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

Si todo anda bien recibirás un mensaje de confirmación similar a este:

Composer (version 1.6.5) successfully installed to: /home/translector/composer.phar

Ahora usa los siguientes comandos para hacer que Composer esté disponible globalmente para todos los usuarios en tu sistema operativo.

sudo mv composer.phar /usr/local/bin/composer
sudo chmod +x /usr/local/bin/composer

Listo, Composer ya está instalado en tu sistema y listo para ser utilizado.

Ejecuta "composer" en el terminal y obtendrás el siguiente mensaje:

   ______
  / ____/___  ____ ___  ____  ____  ________  _____
 / /   / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__  )  __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
                    /_/
Composer version 1.6.5 2018-05-04 11:44:59

Usage:
  command [options] [arguments]

Options:
  -h, --help                     Display this help message
  -q, --quiet                    Do not output any message
  -V, --version                  Display this application version
      --ansi                     Force ANSI output
      --no-ansi                  Disable ANSI output
  -n, --no-interaction           Do not ask any interactive question
      --profile                  Display timing and memory usage information
      --no-plugins               Whether to disable plugins.
  -d, --working-dir=WORKING-DIR  If specified, use the given directory as working directory.
  -v|vv|vvv, --verbose           Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug

Available commands:
  about                Shows the short information about Composer.
  archive              Creates an archive of this composer package.
  browse               Opens the package's repository URL or homepage in your browser.
  check-platform-reqs  Check that platform requirements are satisfied.
  clear-cache          Clears composer's internal package cache.
  clearcache           Clears composer's internal package cache.
  config               Sets config options.
  create-project       Creates new project from a package into given directory.
  depends              Shows which packages cause the given package to be installed.
  diagnose             Diagnoses the system to identify common errors.
  dump-autoload        Dumps the autoloader.
  dumpautoload         Dumps the autoloader.
  exec                 Executes a vendored binary/script.
  global               Allows running commands in the global composer dir ($COMPOSER_HOME).
  help                 Displays help for a command
  home                 Opens the package's repository URL or homepage in your browser.
  info                 Shows information about packages.
  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.
  licenses             Shows information about licenses of dependencies.
  list                 Lists commands
  outdated             Shows a list of installed packages that have updates available, including their latest version.
  prohibits            Shows which packages prevent the given package from being installed.
  remove               Removes a package from the require or require-dev.
  require              Adds required packages to your composer.json and installs them.
  run-script           Runs the scripts defined in composer.json.
  search               Searches for packages.
  self-update          Updates composer.phar to the latest version.
  selfupdate           Updates composer.phar to the latest version.
  show                 Shows information about packages.
  status               Shows a list of locally modified packages, for packages installed from source.
  suggests             Shows package suggestions.
  update               Upgrades your dependencies to the latest version according to composer.json, and updates the composer.lock file.
  upgrade              Upgrades your dependencies to the latest version according to composer.json, and updates the composer.lock file.
  validate             Validates a composer.json and composer.lock.
  why                  Shows which packages cause the given package to be installed.
  why-not              Shows which packages prevent the given package from being installed.

Probablemente necesites instalar también ext-dom, gd y mbstring

sudo apt install php7.2-mbstring
sudo apt install php7.2-xml
sudo apt install php7.2-gd

Si queremos utilizar Drupal Console debemos también instalar la siguiente extensión de php

sudo apt install php7.2-mysql

También hay que instalar la extensión Curl de Php

sudo apt install php7.2-curl

Fuentes:

  • https://tecadmin.net/install-php-composer-on-ubuntu/
  • https://websiteforstudents.com/how-to-install-php-composer-on-ububuntu-16-04-17-10-18-04/
  • https://stackoverflow.com/questions/43408604/php7-install-ext-dom-issue