Quick and dirty script that can auto-pull to keep your repo up-to-date any time something is pushed to the remote repo

github-post-receive-pull.php

<?php

// Edit these to match your environment settings
define( 'BASE_PATH', '/home/username/webapps' );
// This is the path to the git executable
define( 'GIT_PATH', get_full_path( '/git/bin/git' ) );

// Edit this array so the key matches the github repo name and the value is path of the repo relative to the BASE_PATH 
$repository_paths = array(
	'test' => '/git-test'
);

if( isset( $_POST['payload'] ) ) {
	$payload = json_decode( stripslashes( $_POST['payload'] ) );

	if( isset( $repository_paths[ $payload->repository->name ] ) ) {
		$path = get_full_path( $repository_paths[ $payload->repository->name ] );
		
		$cmd = sprintf( 'cd %s; ', $path );
		$cmd .= sprintf( '%s pull', GIT_PATH );
		shell_exec( $cmd );
		
		die( "Executed: $cmd!" );
	}
}

die( 'Dont\'t think you\'re sposed to be here...' );

function get_full_path( $path ) {
	return BASE_PATH . $path;
}

Written for my setup on Webfaction so it's unlikely to work as-is for others. You likely have to tweak the base and git paths.