A local replication entry

I think maybe it's just too early in the morning for me, but I can't seem to get a local entry for replication working. I'm trying to create a script for hourly backups using
pg_basebackup, and here's the command I'm using:

/usr/pgsql-9.3/bin/pg_basebackup -D - -Ft -z -c fast -l hourly.backup > backup_file.gz

The entry in the pg_hba.conf file is:

local replication postgres trust

And the error is: FATAL: no pg_hba.conf entry for replication connection from host "[local]", user "postgres", SSL off, but I have gotten this to work only if I use a "-h
10.10.1.129" option for the command. This only works since another entry in the pg_hba.conf satisfies the command.

Do I have an error with the local entry? Or are local entries even allowed for replication? As this has to be automatically deployed to various servers, I'd prefer to NOT specify
each host's IP address both in pg_hba.conf file and in the script calling the pg_basebackup command. Oh, and at some point when this starts working, I am going to change the user
from postgres to another without superuser capability.
--
Jay