let me ask a more specific question if I have a file with lines that have UserID=somestuff& surrounded by other text how can I substitue the UserID=somestuff for say UserID=foo the file is like this aaaaaaaaaaaaaaaUserID=oldid&bbbbbbbbbbbbbbbbbbbb and I want to make it aaaaaaaaaaaaaaaUserID=newid&bbbbbbbbbbbbbbbbbbbb the substring is UserID=text and ends at the &