Quickly importing new config entities from the command line using Drush

Drush's cset command is a bit picky, but with a few command line options, we can get it to import a yaml file into our site's config:

drush -y --format=yaml cset config.entity.string '' - < config_file.yml

This will put the entirety of config_file.yml into the configuration entity config.entity.string.

The -y is required because drush will ask you if you want add a new entity (and of course you do!). The "trick" if it even is that, is the '' before the - to read from STDIN.