I'm using wp-cli 1.5.1. My server is running php7.2.
I'm not running suhosin. (Some people seem to think that suhosin may cause the same symptom)
When I issue wpcli commands within a non-wordpress directory I get the expected outcome: and error message saying "This does not seem to be a WordPress install."
However, when I run wpcli commands within wordpress directories,the prompt returns quickly without output.
This seems to apply to most variations of 'wpcli plugin', 'wpcli theme', 'wpci search-replace' and 'wp theme'. These are the ones that I've tested.
'wp --version' and 'wp --help' return the expected output'.
What could be happening here?