Looking for a regular expression for this...

[malahal at us.ibm.com]

Hi,
    My string is a multi line string that contains "filename
    <filename>\n" and "host <host>\n" entries among other things.

    For example: s = """ filename X
                    host hostname1
                    blah...
                    host hostname2
                    blah...
                    filename Y
                    host hostname3
                    """
Given a host name, I would like to get its filename (The closest
filename reading backwards from the host line). I could read each line
until I hit the host name, but I am looking for an RE that will do job.
The answer should be "Y" for host hostname3 and "X" for either host
hostname1 or hostname2.

Thanks in advance.

--Malahal.