The docs state, w.r.t. $subject:
The password can be provided either in the primary_conninfo string
or in a separate ~/.pgpass file on the standby server.
I tried this with a database name of "replication" in the .pgpass file,
which matches what we need to use in pg_hba.conf, but it failed
miserably, and only worked when I used a wildcard for the database name
in the .pgpass file.
If this is expected it needs to be documented more clearly; if not, it's
a bug.
I expect this to be quite a common thing to do - many people will be
like me and dislike putting passwords in config files.
cheers
andrerw