Using psql variables in scripts

Would like to use variables in combination with files for common psql
queries, and am using PG 8.1.4.

For example

\set table_name pg_class

select * from pg_tables where tablename = ':table_name';

This returns no rows, even though the customer table exists. It appears
to be search for a table called ":table_name".

I can get this to work by doing the following:

\set table_name '\'pg_class\''

select * from pg_tables where tablename = :table_name;

schemaname | tablename | tableowner | tablespace | hasindexes |
hasrules | hastriggers

------------+-----------+------------+------------+------------+--------
--+-------------

pg_catalog | pg_class | postgres | | t | f
| f

Is there any way to do use variables within quotes?

Thanks,
Corey Horton