including variables in COPY command

[Dinesh <dbhandary(at)mongonet(dot)net>]

Hi ALL,

I am trying to use Copy command to copy data from table to a flat file. 
Here is an example:

copy ( select * from employee where hire_date between begin_date and 
end_date) to '/var/data/text.txt' delimiter ';';

But my problem is the query is not able to read variable begin_date and 
end_date. It works fine when I passed the real value. Has anyone used 
variable within a copy ?  Please let me know.

Thanks,

Dinesh