I have a script that I want to ensure has flushed stdout after ever line
of output. I have $stdout.sync=true but when I tried to do $stdout.fsync
I get an Invalid Argument error. Not what I expect according to the docs.

My goal is that I have a script providing lookups for mod_rewrite in
Apache. It hands me the HTTP_HOST header on $stdin and I return the path 
where it should look for a specific website on $stdout. It seems to work 
well but every now and then it returns the wrong answer. My only two 
possibilities that I can see for this problems are:
1) Apache is asking the script the next request before the first request
is answered. But I am using the RewriteLock directive so Apache should
have the requests synchronized.
2) My other option is that the buffer is not getting flushed. Then
another request comes it and both answers are outputted with the first
answer being the wrong answer.

The script seems to perform perfect when run from the command line. Just
not in Apache. Sometime is returns the right answer sometimes it returns
the wrong answer. Even when make the same request (i.e. refresh).

See http://httpd.apache.org/docs-2.0/mod/mod_rewrite.html if you are
curious on the mod_rewrite semantics. If posting the script would help I
can post that also.

I appreciate any pointers.

Eric