By Linux style copy-paste I mean highlight by dragging left mouse and paste by clicking middle mouse. Doing so to copy from Mathematica 11.0 to an xterm or editor works, but after 65 characters, "\\n" is inserted. This happens if the copied content comes from an Input, Output, or Print cell. If the content comes from a Text cell then there is no problem.
If copying to an xterm (for example a long path name from the output of FindFile), then one can use this longer procedure: highlight, right click, select "Copy as" -> "Plain Text", right click in the xterm (works for KDE Konsole), and then select "Paste". However, it is too long for my liking and it doesn't work for emacs.
By the way, the reason for the "\\n" is because in Mathematica one can type,
to get the output string "abcdef", provided the Enter immediately follows the backslash (i.e., no spaces after it).
I'm guessing that somewhere there is a parameter that sets the 65 character limit. Does anyone know where it is and how best to change it?