psql variable interpolation from command line

I'm at a loss to explain this one:

$ psql -v AUTHOR="'foo'" -c 'select :AUTHOR;'
ERROR: syntax error at or near ":" at character 8

$ psql -v AUTHOR="'foo'"
...
# select :AUTHOR;
?column?
----------
foo
(1 row)

In other words, why won't variable interpolation work when the "-c" flag is
used?

--
Jeff Boes vox 269.226.9550 ext 24
Database Engineer fax 269.349.9076
Nexcerpt, Inc. http://www.nexcerpt.com
...Nexcerpt... Extend your Expertise