[Pharo-users] String replacement

I've got a string which is the header section of an email. I have a regex which will split a header field name from its data (ie, "From: jim@null.com" becomes "From" and "jim@null.com") but some header lines are long and have been continued by inserting a newline and one or more spaces. Before splitting the fields I need to undo these continuations by deleting these combinations of a newline followed by some whitespace. This would certainly be trivial in Perl or any of the normal Linux regex engines but I've spent hours on this today, equipped with the PBE2 chapter, and got nowhere. How do I do this in Pharo? Thanks, Thomas