Updated PHP code to use the Google Sheets API. See usage instructions at http://karl.kranich.org/2015/04/16/google-sheets-api-php/ More examples at https://gist.github.com/karlkranich/afa39e3d778455b38c38

apitest.php

<?php
// apitest.php
// by Karl Kranich - karl.kranich.org
// version 3.1 - edited query section

require_once realpath(dirname(__FILE__) . '/vendor/autoload.php');
include_once "google-api-php-client/examples/templates/base.php";

$client = new Google_Client();

/************************************************
  ATTENTION: Fill in these values, or make sure you
  have set the GOOGLE_APPLICATION_CREDENTIALS
  environment variable. You can get these credentials
  by creating a new Service Account in the
  API console. Be sure to store the key file
  somewhere you can get to it - though in real
  operations you'd want to make sure it wasn't
  accessible from the webserver!
 ************************************************/
putenv("GOOGLE_APPLICATION_CREDENTIALS=service-account-credentials.json");

if ($credentials_file = checkServiceAccountCredentialsFile()) {
  // set the location manually
  $client->setAuthConfig($credentials_file);
} elseif (getenv('GOOGLE_APPLICATION_CREDENTIALS')) {
  // use the application default credentials
  $client->useApplicationDefaultCredentials();
} else {
  echo missingServiceAccountDetailsWarning();
  exit;
}

$client->setApplicationName("Sheets API Testing");
$client->setScopes(['https://www.googleapis.com/auth/drive','https://spreadsheets.google.com/feeds']);

// Some people have reported needing to use the following setAuthConfig command
// which requires the email address of your service account (you can get that from the json file)
// $client->setAuthConfig(["type" => "service_account", "client_email" => "my-service-account@developer.gserviceaccount.com"]);

// The file ID was copied from a URL while editing the sheet in Chrome
$fileId = '15byt2tfdaHmaEpdwd4UYGWs70Eaej8edkQ2dS8x4mIk';

// Access Token is used for Steps 2 and beyond
$tokenArray = $client->fetchAccessTokenWithAssertion();
$accessToken = $tokenArray["access_token"];

// Section 1: Uncomment to get file metadata with the drive service
// This is also the service that would be used to create a new spreadsheet file
$service = new Google_Service_Drive($client);
$results = $service->files->get($fileId);
var_dump($results);

// Section 2: Uncomment to get list of worksheets
// $url = "https://spreadsheets.google.com/feeds/worksheets/$fileId/private/full";
// $method = 'GET';
// $headers = ["Authorization" => "Bearer $accessToken"];
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url);
// $body = $resp->getBody()->getContents();
// $code = $resp->getStatusCode();
// $reason = $resp->getReasonPhrase();
// echo "$code : $reason\n\n";
// echo "$body\n";

// Section 3: Uncomment to get the table data
// $url = "https://spreadsheets.google.com/feeds/list/$fileId/od6/private/full";
// $method = 'GET';
// $headers = ["Authorization" => "Bearer $accessToken", "GData-Version" => "3.0"];
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url);
// $body = $resp->getBody()->getContents();
// $code = $resp->getStatusCode();
// $reason = $resp->getReasonPhrase();
// echo "$code : $reason\n\n";
// echo "$body\n";

// Section 4: Uncomment to add a row to the sheet
// $url = "https://spreadsheets.google.com/feeds/list/$fileId/od6/private/full";
// $method = 'POST';
// $headers = ["Authorization" => "Bearer $accessToken", 'Content-Type' => 'application/atom+xml'];
// $postBody = '<entry xmlns="http://www.w3.org/2005/Atom" xmlns:gsx="http://schemas.google.com/spreadsheets/2006/extended"><gsx:gear>more gear</gsx:gear><gsx:quantity>44</gsx:quantity></entry>';
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url, ['body' => $postBody]);
// $body = $resp->getBody()->getContents();
// $code = $resp->getStatusCode();
// $reason = $resp->getReasonPhrase();
// echo "$code : $reason\n\n";
// echo "$body\n";

// Section 5: Uncomment to edit a row
// You'll need to get the etag and row ID, and send a PUT request to the edit URL
// $rowid = 'cre1l';                 // got this and the etag from the table data output from section 3
// $etag = 'NQ8SVE8fDSt7ImA.';
// $url = "https://spreadsheets.google.com/feeds/list/$fileId/od6/private/full/$rowid";
// $method = 'PUT';
// $headers = ["Authorization" => "Bearer $accessToken", 'Content-Type' => 'application/atom+xml', 'GData-Version' => '3.0'];
// $postBody = "<entry xmlns=\"http://www.w3.org/2005/Atom\" xmlns:gsx=\"http://schemas.google.com/spreadsheets/2006/extended\" xmlns:gd=\"http://schemas.google.com/g/2005\" gd:etag='&quot;$etag&quot;'><id>https://spreadsheets.google.com/feeds/list/$fileid/od6/$rowid</id><gsx:gear>phones</gsx:gear><gsx:quantity>6</gsx:quantity></entry>";
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url, ['body' => $postBody]);
// $body = $resp->getBody()->getContents();
// $code = $resp->getStatusCode();
// $reason = $resp->getReasonPhrase();
// echo "$code : $reason\n\n";
// echo "$body\n";

// Section 6: Uncomment to parse table data with SimpleXML
// $url = "https://spreadsheets.google.com/feeds/list/$fileId/od6/private/full";
// $method = 'GET';
// $headers = ["Authorization" => "Bearer $accessToken", "GData-Version" => "3.0"];
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url);
// $body = $resp->getBody()->getContents();
// $tableXML = simplexml_load_string($body);
// echo "Rows:\n";
// foreach ($tableXML->entry as $entry) {
//   $etag = $entry->attributes('gd', TRUE);
//   $id = $entry->id;
//   echo "etag: $etag\n";
//   echo "id: $id\n";
//   foreach ($entry->children('gsx', TRUE) as $column) {
//     $colName = $column->getName();
//     $colValue = $column;
//     echo "$colName : $colValue\n";
//   }
// }

// Section 7: Uncomment to query for a subset of rows and parse data with SimpleXML
// $url = "https://spreadsheets.google.com/feeds/list/$fileId/od6/private/full?sq=quantity>9";
// $myQuery = 'quantity>9';  // and here is an example with a space in it: $myQuery = 'gear="mifi device"';
// $method = 'GET';
// $headers = ["Authorization" => "Bearer $accessToken", "GData-Version" => "3.0"];
// $httpClient = new GuzzleHttp\Client(['headers' => $headers]);
// $resp = $httpClient->request($method, $url, ['query' => ['sq' => $myQuery]]);
// $body = $resp->getBody()->getContents();
// $tableXML = simplexml_load_string($body);
// echo "Rows:\n";
// foreach ($tableXML->entry as $entry) {
//   $etag = $entry->attributes('gd', TRUE);
//   $id = $entry->id;
//   echo "etag: $etag\n";
//   echo "id: $id\n";
//   foreach ($entry->children('gsx', TRUE) as $column) {
//     $colName = $column->getName();
//     $colValue = $column;
//     echo "$colName : $colValue\n";
//   }
// }

@flo62134, you're missing the base.php file