I'm using shared hosting for a website and can't execute commands there. Aside from running composer via php script request that I request via browser, I usually use this workflow:

• Make sure you have php installed locally.
• Make directory on desktop.
• download composer.phar from https://getcomposer.org/download/ (under header *Manual Download) and place it in the directory.

• make a file composer.json paste in it the following contents

   {
       "require": {
           "coinbase/coinbase": "~2.0"
       }
   }
  

• Browse to the directory with the shell of your choice(bash, git-bash, cmd, windows bash)

• type php composer.phar update
• Upload the vendor directory to your webserver via ftp or whatever mechanic you use.

• include in your php project where you load your libraries(modify path to where you uploaded the vendor dir so it will include that autoload file)

  require_once('vendor/autoload.php');
  

This way you get the benefit of dependency management and you don't have to include manually all the gazillion of files and download all the dependencies manually, and updating them is just as easy as typing php composer.phar update and then replacing the vendor dir on your server with the new one.

An alternative solution that worked for me (since php-download was down) can be done by making your own little local composer downloader.

1. Download and install XAMPP locally: https://www.apachefriends.org/index.html
2. Download and install composer locally: https://getcomposer.org/download/
3. Open commandprompt, navigate to say c:\temp and and simply type the composer dependancy, for example: composer require league/oauth2-client
4. Copy the files from your c:\temp folder to your web host using an FTP program
5. Add this to the top of your php: require("vendor/autoload.php");

This is not the ultimate solution but for me it was a big help for most of the cases: https://github.com/Wilkins/composer-file-loader

Allow you to load composer.json file just as composer would do it. This allow you to load composer.json file without composer (so theorically PHP 5.2 is enough)

I know the question is old but I hope it will help someone.

I had to do this for an FTP server I didn't have SSH access to. The site listed in here worked, then I realized you can just do a composer install on your own server (using your target's PHP version), then copy all the files over.

Analizing the problem

The problem in installing the dependencies without Composer is the autoloading system.

Composer use a homemade autoloader based on an array map, this is a de-facto standard. But this autoloading system, "fortunally" in this case, is not PSR-4 compliant.

PSR-4 is the de-iure standard for autoload a class in PHP, so you can't escape from autoloading. You must use one of them.

Solution Proposal

Require the custom autoload.php file early in your source code. Manually configure this brilliant PSR-4 autoloader to autoload a VendorClass in a VendorNamespace anywhere in your code.

Real life example

Look at this example: I have a legacy project who can't and won't use Composer. This project can be speed up in development with this fantastic package for command line scripts. This is my project directory structure:

 - src
 - tests
 - vendor (not the Composer's one)

This package has this directory structure:

 - examples
 - src
   - Commando
 - tests

The only thing I need is the src folder. Placing this folder in my vendor folder would be fine. So my custom autoloader would be like this:

// Constants
$base_path = "path\to\my\project";
$autoloader_class = '\vendor\MarcoConsiglio-Wichee\PSR-4-Autoloading\Psr4AutoloaderClass.php';
define("BASE_PATH", str_replace("\\", DIRECTORY_SEPARATOR, $base_path));

// Autoloader
require_once BASE_PATH.'\vendor\MarcoConsiglio-Wichee\PSR-4-Autoloading\Psr4AutoloaderClass.php';

// Init the autoloader.
$package = [
    "nategood\commando" => [
        "namespace" => "Commando",
        "path" => str_replace("\\", DIRECTORY_SEPARATOR, '\vendor\nategood\commando\src\Commando')
    ],
    "kevinlebrun\colors.php" => [
        "namespace" => "Colors",
        "path" => str_replace("\\", DIRECTORY_SEPARATOR, '\vendor\kevinlebrun\colors.php\src\Colors')
    ]
];

// Register namespaces.
$loader = new \PSR4\Psr4AutoloaderClass;
$loader->register();
                      // Namespace                                      // Path to source
$loader->addNamespace($package["nategood\commando"]["namespace"],       BASE_PATH.$package["nategood\commando"]["path"]);
$loader->addNamespace($package["nategood\commando"]["namespace"],       BASE_PATH.$package["nategood\commando"]["path"]."\Util");
$loader->addNamespace($package["kevinlebrun\colors.php"]["namespace"],  BASE_PATH.$package["kevinlebrun\colors.php"]["path"]);

Now I can use the command package anywhere in my project!

Pros & Cons

This solution allow you to:

• Easely and manually build your own custom autoloader (you only need to specify the VendorNamespace and the folder(s) where search for VendorClasses in the VendorNamespace.
• Freely organize your composer dependency anywhere in your project folder (and why not, outside it)
• Import a composer package as is in your project (either downloading locally with Composer or cloning the package repository) or a relevant part of it (i.e removing composer.json file or files that require the composer autoloader).

Cons:

• Manually build your custom autoloader means to work on every required dependency of your project (i hope not a lot).
• Mistakes in package source paths can be tedious and frustrating.
• Works only with PSR-4 compliant file names (i.e. can't use a A.class.php file name)

I had to make a python script that generates the autoload.php.

1. In composer.json, find the autoload.psr-4 and copy the library path (in my case src/Pecee):

"autoload": {
    "psr-4": {
        "Pecee\\": "src/Pecee"
    }
}

2. Copy and paste this python script and replace the path with yours.

import os

# adjust the path (in my case the script was already in `src` directory)
path = "."

with open("autoload.php", "w") as file:
    file.write("<?php\n")

    for item in os.walk(path):
        dirname = item[0]
        for filename in item[2]:
            file.write("require_once \"" + dirname + "/" + filename + "\";\n")

This script generates an autoload.php file that can be imported into a php file. Example:

<?php
require_once "./Pecee/Exceptions/InvalidArgumentException.php";
require_once "./Pecee/SimpleRouter/SimpleRouter.php";
require_once "./Pecee/SimpleRouter/IRouterBootManager.php";
require_once "./Pecee/SimpleRouter/Router.php";
...

You will need to change the order of require_once based on the error messages that will popup.

Enable error messages and import autoload.php:

ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');
error_reporting(E_ALL);

require_once "./autoload.php";