GNU bug report logs - #27361
24.4; eshell/echo silently ignores -n argument

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Phil Hagelberg <phil <at> hagelb.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.4; eshell/echo silently ignores -n argument
Date: Wed, 14 Jun 2017 09:15:41 -0700

When using eshell, the `echo' built-in doesn't respect the -n argument,
which is supposed to suppress the trailing newline.

Sometimes this is not a problem because you can see for yourself that
eshell did the wrong thing, but if you are piping it directly to another
command, it's easy to miss.

The eshell/echo function should be changed to either accept the -n
argument and omit the newline, or it should complain that -n is not a
supported argument.



In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5)
 of 2015-03-07 on trouble, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11604000
System Description:	Debian GNU/Linux 8.8 (jessie)

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For information about GNU Emacs and the GNU system, type C-h C-a.
History item: 128

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Message #8 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: npostavs <at> users.sourceforge.net
To: Phil Hagelberg <phil <at> hagelb.org>
Cc: 27361 <at> debbugs.gnu.org
Subject: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Mon, 19 Jun 2017 00:11:34 -0400

Phil Hagelberg <phil <at> hagelb.org> writes:

> When using eshell, the `echo' built-in doesn't respect the -n argument,
> which is supposed to suppress the trailing newline.
>
> Sometimes this is not a problem because you can see for yourself that
> eshell did the wrong thing, but if you are piping it directly to another
> command, it's easy to miss.
>
> The eshell/echo function should be changed to either accept the -n
> argument and omit the newline, or it should complain that -n is not a
> supported argument.

It's not ignored, but eshell always adds a newline before the prompt.
Furthermore, the argument has the opposite sense to the traditional
shell interpretation:

    ~/src $ echo x | od -c
    0000000   x
    0000001
    ~/src $ echo -n x | od -c
    0000000   x  \n
    0000002

Message #11 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Phil Hagelberg <phil <at> hagelb.org>
To: npostavs <at> users.sourceforge.net
Cc: 27361 <at> debbugs.gnu.org
Subject: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Mon, 19 Jun 2017 08:22:53 -0700

[Message part 1 (text/plain, inline)]

npostavs <at> users.sourceforge.net writes:

> It's not ignored, but eshell always adds a newline before the prompt.
> Furthermore, the argument has the opposite sense to the traditional
> shell interpretation

Ah, I see. Yeah, doing the opposite of what the user asked for in both
cases is much worse than simply ignoring the argument when it's present.

-Phil

[signature.asc (application/pgp-signature, inline)]

Message #14 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: Phil Hagelberg <phil <at> hagelb.org>
Cc: 27361 <at> debbugs.gnu.org, npostavs <at> users.sourceforge.net
Subject: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Mon, 19 Jun 2017 21:57:31 -0400

echo -n is famously non-portable.
Perhaps eshell is trying to make a point. ;)
echo --help does document the -n behaviour, and it's been like that
since always.
With eshell-plain-echo-behavior set, -n is simply ignored.
I would have thought you must have eshell-plain-echo-behavior set
if you want anything like "standard" echo behaviour.

Message #19 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Glenn Morris <rgm <at> gnu.org>
To: Phil Hagelberg <phil <at> hagelb.org>
Cc: 27361 <at> debbugs.gnu.org, npostavs <at> users.sourceforge.net
Subject: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Mon, 19 Jun 2017 22:17:26 -0400

It seems easy to get the behaviour that you want, for the
eshell-plain-echo-behavior case, which is the only relevant one.
At the same time, we can fix eshell/printnl for that case,
to avoid the doubled newlines that it currently gives.

I don't know how to explain in --help what -n means though. :)

--- a/lisp/eshell/em-basic.el
+++ b/lisp/eshell/em-basic.el
@@ -88,7 +88,8 @@ eshell-echo
 It returns a formatted value that should be passed to `eshell-print'
 or `eshell-printn' for display."
   (if eshell-plain-echo-behavior
-      (concat (apply 'eshell-flatten-and-stringify args) "\n")
+      (concat (apply 'eshell-flatten-and-stringify args)
+	      (unless output-newline "\n"))
     (let ((value
 	   (cond
 	    ((= (length args) 0) "")
@@ -126,7 +127,8 @@ eshell/printnl
   "Print out each of the arguments, separated by newlines."
   (let ((elems (eshell-flatten-list args)))
     (while elems
-      (eshell-printn (eshell-echo (list (car elems))))
+      (eshell-printn (eshell-echo (list (car elems))
+				  eshell-plain-echo-behavior))
       (setq elems (cdr elems)))))
 
 (defun eshell/listify (&rest args)

Message #22 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 27361 <at> debbugs.gnu.org, Phil Hagelberg <phil <at> hagelb.org>,
 npostavs <at> users.sourceforge.net
Subject: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Tue, 15 Sep 2020 17:27:12 +0200

Glenn Morris <rgm <at> gnu.org> writes:

> It seems easy to get the behaviour that you want, for the
> eshell-plain-echo-behavior case, which is the only relevant one.
> At the same time, we can fix eshell/printnl for that case,
> to avoid the doubled newlines that it currently gives.
>
> I don't know how to explain in --help what -n means though. :)

[...]

> -      (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

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #25 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Jim Porter <jporterbugs <at> gmail.com>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Glenn Morris <rgm <at> gnu.org>, 27361 <at> debbugs.gnu.org
Subject: Re: Re: bug#27361: 24.4; eshell/echo silently ignores -n argument
Date: Sat, 15 Jan 2022 23:19:50 -0800

[Message part 1 (text/plain, inline)]

On 9/15/2020 8:27 AM, Lars Ingebrigtsen wrote:
> Glenn Morris <rgm <at> 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.

[0001-In-Eshell-allow-n-to-suppress-the-trailing-newline-f.patch (text/plain, attachment)]

Message #28 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Jim Porter <jporterbugs <at> gmail.com>
Cc: Glenn Morris <rgm <at> gnu.org>, 27361 <at> debbugs.gnu.org
Subject: Re: bug#27361: Re: bug#27361: 24.4; eshell/echo silently ignores -n
 argument
Date: Thu, 20 Jan 2022 10:36:05 +0100

Jim Porter <jporterbugs <at> gmail.com> writes:

> 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

Thanks; applied to Emacs 29.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Message #33 received at 27361 <at> debbugs.gnu.org (full text, mbox):

From: Jim Porter <jporterbugs <at> gmail.com>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Glenn Morris <rgm <at> gnu.org>, 27361 <at> debbugs.gnu.org
Subject: Re: bug#27361: Re: bug#27361: 24.4; eshell/echo silently ignores -n
 argument
Date: Thu, 20 Jan 2022 17:27:32 -0800

On 1/20/2022 1:36 AM, Lars Ingebrigtsen wrote:
> Jim Porter <jporterbugs <at> gmail.com> writes:
> 
>> 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
> 
> Thanks; applied to Emacs 29.

Thanks. Hopefully the warning about using "-n" with Lisp-friendly echo 
isn't too obtrusive for people, but if it is, we could probably replace 
it with `message'.

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