Help with Regular Expression

[plug-discuss@lists.plug.phoenix.az.us]

Hi All, 

I seem to be having a lot of trouble with what seems should be a simple regex.

I have a database full of research paper abstracts and I would like to strip all newlines from them. This would include 
\n, \r, and \r\n characters.  However, if there are two consecutive newlines (i.e. new paragraph) I would like to keep 
those in tact.

I have written the script in PHP to pull each field from the database, perform said regex and then update the field 
with the new data.  All I need is a regex that works.  I'm using the Perl compatible regex within PHP.

Any help would be appreciated.

Thanks,
Peter