displays groups belonging to a specified user and users belonging to a specified group

getUserGroupMemberships.php

<?php

if($argc !== 3) {
  print('Usage: php -f ' . $argv[0] . ' UID GID' . PHP_EOL);
  die;
}

require_once 'lib/base.php';

\OC_App::loadApps(array('authentication'));

$uid = $argv[1];
$gid = $argv[2];

$uM = \OC::$server->getUserManager();
$user = $uM->get($uid);
if(!$user instanceof \OCP\IUser) {
  die('Invalid UserID');
}

$gM = \OC::$server->getGroupManager();
$groups = $gM->getUserGroups($user);
print($user->getDisplayName() . ' is member of following groups:' . PHP_EOL);
if(empty($groups)) {
  print('(none)' . PHP_EOL);
} else {
  foreach($groups as $group) {
    print($group->getGID() . PHP_EOL);
  }
}

$group = $gM->get($gid);
if(!$group instanceof \OCP\IGroup) {
  die('Invalid GroupID');
}
$users = $gM->displayNamesInGroup($gid);
print(PHP_EOL);
print($group->getGID() . ' has following members:' . PHP_EOL);
if(empty($users)) {
  print('(none)' . PHP_EOL);
} else {
  foreach($users as $id => $user) {
    print($user . ' (' . $id . ')' . PHP_EOL);
  }
}