wp-cli/wp-cli — pull request #1144 by danielbachhuber (2014-04-21 23:51:14+00:00)
Title: `wp plugin update` runs with missing argument, 

`wp plugin update` accepts calls without `` or `--all`, makes no updates, and succeeds. ;)

Can we print a warning message instead?

wp plugin update
Success: Updated 0/0 plugins.
# oops, I meant --all
wp plugin update --all
Enabling Maintenance mode...
# …
Success: Updated 3/3 plugins.