How to check if a postgres user exists?

Question

createuser allows creation of a user (ROLE) in PostgreSQL. Is there a simple way to check if that user(name) exists already? Otherwise createuser returns with an er

Answer 1

SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'

And in terms of command line (thanks to Erwin):

psql postgres -tAc "SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'"

Yields 1 if found and nothing else.

That is:

psql postgres -tAc "SELECT 1 FROM pg_roles WHERE rolname='USR_NAME'" | grep -q 1 || createuser ...