Minimuist pull me script that work with Github hook

pullme.php

<?php

/* host machine settings */
$GIT_BIN = '/usr/local/bin/git';
$LOCAL_USER = 'www';

/* remote repo settings */
$REMOTE = 'origin';
$BRANCH = 'production';

header('Content-Type: text/plain; charset=UTF-8');

if (!isset($argv) && $_SERVER['REQUEST_METHOD'] !== 'POST') {
  print <<<EOL
Error: Use POST request to update.
For testing, use 'curl -d dummy=data'.

EOL;
  exit;
}

if ( trim(exec('whoami')) !== $LOCAL_USER) {
  print 'Error: Must run as the specified user.';
  exit;
}

system(
  "$GIT_BIN fetch $REMOTE 2>&1 && " . 
  "$GIT_BIN checkout -q $REMOTE/$BRANCH 2>&1 && " .
  "$GIT_BIN submodule -q update --init 2>&1; " .
  "$GIT_BIN log -1 2>&1"
);