Help with Regular Expression

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