/Users/paul/Applications/Test.app/Contents/MacOS/My Chrome

gistfile1.php

#!/usr/bin/env php

<?php

// Read prefs file
$prefsRaw = file_get_contents('/Users/ ** USERNAME ** /Library/Application Support/Google/Chrome/Default/Preferences');
$prefsJson = json_decode($prefsRaw);

// Rewrite (or create) "pinned_tabs" with fixed list of urls.
$myUrls = array(
  'https://www.facebook.com/',
  'https://www.twitter.com',
);
$objectUrls = array();
foreach ($myUrls as $url) {
  $object = new StdClass();
  $object->url = $url;
  $objectUrls[] = $object;
}

// Save prefs
$prefsJson->pinned_tabs = $objectUrls;
$newPrefsRaw = json_encode($prefsJson, JSON_PRETTY_PRINT);
file_put_contents('/Users/ ** USERNAME ** /Library/Application Support/Google/Chrome/Default/Preferences', $newPrefsRaw);

// Launch Chrome
exec('/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome >/dev/null');
exit;