On 9/15/2020 8:27 AM, Lars Ingebrigtsen wrote:
> Glenn Morris <rgm@gnu.org> writes:
> 
>> -      (concat (apply 'eshell-flatten-and-stringify args) "\n")
>> +      (concat (apply 'eshell-flatten-and-stringify args)
>> +	      (unless output-newline "\n"))
> 
> Hm...  with or without the patch, and with eshell-plain-echo-behavior
> set, I don't see any difference?
> 
> I still get this in eshell:
> 
> ~/src/emacs/trunk $ echo -n foo; echo bar
> foo
> bar

I think this is due to `eshell-lisp-command' insisting that a newline is 
inserted after the output of *every* Lisp command (when executed 
interactively). It's easier to see what "-n" does by eval'ing:

   (eshell-command-result "echo hi")
   ;; and
   (eshell-command-result "echo -n hi")

One solution to this bug would be to set `eshell-ensure-newline-p' to 
nil inside `eshell-echo'; then it will opt out of `eshell-lisp-command's 
trailing-newline insertion.

I've attached a patch that does this, as well as (hopefully) resolving 
the unusual meaning of "-n" when echo outputs a Lisp-friendly result 
(i.e. when `eshell-plain-echo-behavior' is nil). Now, it warns the user 
to use "-N" instead if they want to add a trailing newline. Then, one 
day, the old meaning of "-n" can be removed. I'm not sure if this is the 
best way to emit a warning about this though; I wanted something that 
doesn't interfere with any Eshell scripts, but `display-warning' is a 
bit in-your-face.

I also simplified the logic of `eshell/printnl'. Since the way it called 
`eshell-echo' always resulted in it printing the stringified form of 
each argument, it's simpler just to call `eshell-stringify' directly.

Finally, I added a bit more detail about echo to the Eshell manual 
(taken partly from the commentary of eshell/em-basic.el), since I didn't 
quite understand its behavior initially.