Setting global parameter in Postgres 8.3

Hi All,

Is there any way we can set the global parameter in Postgres 8.3?

As I have a sql script which need to accept some parameter at run time.
For example I have sql script for creating tablespaces called
"create_tablespace.sql"

Inside the sql script I have the following statements

CREATE TABLESPACE bank_index_tbsp OWNER bank LOCATION
'$drive/data/bank/index_tbsp';

CREATE TABLESPACE bank_master_tbsp OWNER bank LOCATION
'$drive/data/bank/master_tbsp';

CREATE TABLESPACE bank_static_tbsp OWNER bank LOCATION '$drive
/data/bank/static_tbsp';

I need to replace the $drive with a absoulte location in order to create
the tablespaces at run time.So is there any way I can pass parameter to
sql file at the time of execuitng it or is there any way I can set a
global parameter which will repalce the $drive similar to the way
postregs converts or maps the $libdir parameter to the absolute path of
the "Lib" location of postgres.

Any help and suggestion will be really helpful.

Many thanks in advance