update only if single row

Here's the way I do it now:

select * from contact where email ~* 'rvro';
if I get a single row in the result then I enter:
update contact set bounce=1 where email ~* 'rvro';

Can I combine this into a single SQL statement with the following
requirements:
1) the update is only performed if a single row is selected
2) I only enter the selection string ('rvro' in this case) once in the
command?

Frank