while(<DATA>){
	if(/.*transaction="([^"]*)".*document_mode="([^"]*)".*/){
		print "$1_$2.xml\n";
	}
}
__DATA__
<PURCHASE_10 partner="food" version="1.50" timestamp="2009-03-10T09:56:55" transaction="PURCHASEORDER" document_mode="abc"> 
</PURCHASE_10>