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
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