Run composer command from php script, controller, web,

composer.json

{
    "name": "hechoendrupal/composer-ui",
    "description": "Composer UI",
    "minimum-stability": "dev",
    "authors": [
        {
            "name": "David Flore",
            "email": "dmouse.x@gmail.com"
        }
    ],
    "require": {
        "composer/composer": "1.0.0-alpha7"
    }
}

run_composer.php

<?php                                               

use Composer\Factory;                               
use Composer\IO\ConsoleIO;                          
use Symfony\Component\Console\Input\ArgvInput;      
use Symfony\Component\Console\Helper\HelperSet;     
use Symfony\Component\Console\Output\ConsoleOutput; 

use Composer\Command\UpdateCommand;                 

include __DIR__ . '/vendor/autoload.php';           

$input = new ArgvInput(array());    
$output = new ConsoleOutput();                      
$helper = new HelperSet();

$io = new ConsoleIO($input,$output,$helper);        
$composer = Factory::create($io);                   

$update = new UpdateCommand();                      
$update->setComposer($composer);                    
$update->run($input,$output);