Problem

What command-line do you have to use for using Composer ?

Solution

In documentation you will find

$> php composer.phar <command> 

and

$> composer <command>

You will use the command-line according to your installation.

 LocallyGlobally

Command-line

$> php composer.phar$> composer

Advantages

No rights needed
No configuration needed (out of the box)
Every user on the server can access to composer CLI
You have your Composer outside your web RootDirectory

Installation

Locally

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


or (according to your user rights on your system)

php -r "readfile('https://getcomposer.org/installer');" | php

Globally

curl -sS https://getcomposer.org/installer | php mv composer.phar /usr/local/bin/composer
See the official Composer documentation for further documentation.