Drupal - If you update a routes file in Drupal 8 how do you clear the cache?
You can use
drush ev '\Drupal::service("router.builder")->rebuild();'
to rebuild the routing information without clearing all the caches.
An alternative to drush is drupal console, which you can then use as:
drupal router:rebuild
Which is a little less typing than the drush ev
answer (and a tinsy bit faster, too).
To install drupal console
curl -LSs http://drupalconsole.com/installer | php
mv console.phar /path/to/a/suitable/bin/drupal
drush cc router
when using drush 9 do the trick now :-)