Using Substitution Variables In PostgreSQL

Hi All,

I wanted to find out how to use a substitution variable in an SQL statement
that would cause the user to be prompted for a value. Something similar to
the ampersand (&&) in ORACLE.

For example, given the SQL statement below:
SELECT <col1>,<col2>,<col3>
FROM <table>
WHERE <col5> = 35

I want the user to be prompted for the value in the WHERE (filter) clause,
e.g.
SELECT <col1>,<col2>,<col3>
FROM <table>
WHERE <col5> = ?

I would be glad if someone could point me in the right direction.