GNU bug report logs - #21416
"--" syntax for ignoring flags doesn't seem to work right with GNU /bin/echo

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

From: "Robert \"Finny\" Merrill" <rfm <at> arista.com>
To: bug-coreutils <at> gnu.org
Subject: "--" syntax for ignoring flags doesn't seem to work right with GNU
 /bin/echo
Date: Fri, 4 Sep 2015 11:57:30 -0700

~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo --help
Usage: /bin/echo [SHORT-OPTION]... [STRING]...
  or:  /bin/echo LONG-OPTION
Echo the STRING(s) to standard output.
*snip*
~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo -- --help
-- --help
~/workspaces/diags-dev/s1 @bs360.sjc>


There doesn't seem to be a way to get /bin/echo to output the string "--help"

Message #12 received at 21416-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: "Robert \"Finny\" Merrill" <rfm <at> arista.com>, 21416-done <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 13:26:42 -0600

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

tag 21416 notabug
thanks

On 09/04/2015 12:57 PM, Robert "Finny" Merrill wrote:
> ~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo --help
> Usage: /bin/echo [SHORT-OPTION]... [STRING]...
>   or:  /bin/echo LONG-OPTION
> Echo the STRING(s) to standard output.
> *snip*

This is a GNU extension; it is not POSIX compliant, but can easily be
overridden, as shown below.

> ~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo -- --help
> -- --help

Thanks for the report. However, this is working as required by POSIX:

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html

    "The echo utility shall not recognize the "--" argument in the
manner specified by Guideline 10 of XBD Utility Syntax Guidelines; "--"
shall be recognized as a string operand."

    "Implementations shall not support any options."

> 
> There doesn't seem to be a way to get /bin/echo to output the string "--help"

Ah, but there is:

$ POSIXLY_CORRECT=1 /bin/echo --help
--help

Also, POSIX says that 'echo' is outdated (not only because it violates
the standard syntax rules, but also because it has non-portable handling
of \), and that you should strongly consider using printf, in which
case, you would do:

$ printf -- %s\\n --help
--help

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #15 received at 21416-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: "Robert \"Finny\" Merrill" <rfm <at> arista.com>, 21416-done <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 16:05:49 -0600

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

On 09/04/2015 01:30 PM, Robert "Finny" Merrill wrote:
> unicasting so it doesn't reopen the bug:

[re-adding the list with permission]
The bug-tracker is perfectly fine with adding additional comments even
to a closed bug; merely replying doesn't reopen a bug report.

> 
> If POSIX says not to recognize "--" doesn't "not recognize" mean it
> shouldn't do anything at all? In that case, you're not actually
> following it since -- causes different behavior :)

You've quoted incomplete context, which changed the meaning.

>> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html
>>
>>     "The echo utility shall not recognize the "--" argument in the
>> manner specified by Guideline 10 of XBD Utility Syntax Guidelines; "--"
>> shall be recognized as a string operand."
>>
>>     "Implementations shall not support any options."

It's not "shall not be recognized [ever]", but "shall not be recognized
in the manner [common to most utilities].  The very next phrase says
that it "shall be recognized as a string operand".

Or put another way, as a special case for the 'echo' utility, '--' shall
be treated the same as any other argument, and always be output
literally, rather than being recognized as the special elided
end-of-options marker, because 'echo' does not understand options (at
least when POSIX rules are in effect).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #18 received at 21416-done <at> debbugs.gnu.org (full text, mbox):

From: "Robert \"Finny\" Merrill" <rfm <at> arista.com>
To: Eric Blake <eblake <at> redhat.com>
Cc: 21416-done <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 15:23:18 -0700

On Fri, Sep 4, 2015 at 3:05 PM, Eric Blake <eblake <at> redhat.com> wrote:
> On 09/04/2015 01:30 PM, Robert "Finny" Merrill wrote:
> It's not "shall not be recognized [ever]", but "shall not be recognized
> in the manner [common to most utilities].  The very next phrase says
> that it "shall be recognized as a string operand".
>
> Or put another way, as a special case for the 'echo' utility, '--' shall
> be treated the same as any other argument, and always be output
> literally, rather than being recognized as the special elided
> end-of-options marker, because 'echo' does not understand options (at
> least when POSIX rules are in effect).

So then, when POSIX rules /aren't/ in effect, why not have -- work as
it usually does, since we're already breaking those rules by accepting
the --help option?

Message #21 received at 21416-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: "Robert \"Finny\" Merrill" <rfm <at> arista.com>
Cc: 21416-done <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 16:34:42 -0600

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

On 09/04/2015 04:23 PM, Robert "Finny" Merrill wrote:
> On Fri, Sep 4, 2015 at 3:05 PM, Eric Blake <eblake <at> redhat.com> wrote:
>> On 09/04/2015 01:30 PM, Robert "Finny" Merrill wrote:
>> It's not "shall not be recognized [ever]", but "shall not be recognized
>> in the manner [common to most utilities].  The very next phrase says
>> that it "shall be recognized as a string operand".
>>
>> Or put another way, as a special case for the 'echo' utility, '--' shall
>> be treated the same as any other argument, and always be output
>> literally, rather than being recognized as the special elided
>> end-of-options marker, because 'echo' does not understand options (at
>> least when POSIX rules are in effect).
> 
> So then, when POSIX rules /aren't/ in effect, why not have -- work as
> it usually does, since we're already breaking those rules by accepting
> the --help option?

Because then coreutils' echo would needlessly differ from bash's echo,
and because who knows what existing scripts have come to rely on the
behavior and might break as a result.  The use of
POSIXLY_CORRECT=anything to change behavior is not something done
lightly, and we are loathe to make it control more than a bare minimum
of behavior changes.

[As it is, bash has a bug:
$ (shopt -s xpg_echo; echo -e)

should output '-e', but currently outputs nothing.  Also, bash does not
quite treat POSIXLY_CORRECT=1 (also spelled 'set -o posix') as the
override to turn on full POSIX compliance, as it leaves xpg_echo as a
separate knob; ideally, turning on posix compliance in bash should turn
on xpg_echo - but enough people are used to the old behavior that it was
decided to keep the knobs separate]

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #24 received at 21416-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: "Robert \"Finny\" Merrill" <rfm <at> arista.com>
Cc: 21416-done <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 16:42:48 -0600

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

On 09/04/2015 04:34 PM, Eric Blake wrote:
> [As it is, bash has a bug:
> $ (shopt -s xpg_echo; echo -e)
> 
> should output '-e', but currently outputs nothing.  Also, bash does not
> quite treat POSIXLY_CORRECT=1 (also spelled 'set -o posix') as the
> override to turn on full POSIX compliance, as it leaves xpg_echo as a
> separate knob; ideally, turning on posix compliance in bash should turn
> on xpg_echo - but enough people are used to the old behavior that it was
> decided to keep the knobs separate]

Maybe I spoke too soon. It looks like bash needs BOTH xpg_echo and posix
mode at the same time, either one in isolation is not enough:

$ for opt in '' 'shopt -s xpg_echo' 'set -o posix' \
     'shopt -s xpg_echo; set -o posix'; do
    bash -c "echo 'trying $opt'; ${opt:-:}; echo -e"
  done
trying

trying shopt -s xpg_echo

trying set -o posix

trying shopt -s xpg_echo; set -o posix
-e

$

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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Message #27 received at 21416 <at> debbugs.gnu.org (full text, mbox):

From: Bob Proulx <bob <at> proulx.com>
To: "Robert \"Finny\" Merrill" <rfm <at> arista.com>
Cc: 21416 <at> debbugs.gnu.org
Subject: Re: bug#21416: "--" syntax for ignoring flags doesn't seem to work
 right with GNU /bin/echo
Date: Fri, 4 Sep 2015 19:22:04 -0600

Robert "Finny" Merrill wrote:
> ~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo --help
> Usage: /bin/echo [SHORT-OPTION]... [STRING]...
>   or:  /bin/echo LONG-OPTION
> Echo the STRING(s) to standard output.
> *snip*
> ~/workspaces/diags-dev/s1 @bs360.sjc> /bin/echo -- --help
> -- --help
> ~/workspaces/diags-dev/s1 @bs360.sjc>

Under what actual live conditions in the wild would someone be using
/bin/echo in this manor?

Most shell interpreters used for scripts will have a shell builtin
version of echo.

  $ ls -log /bin/sh
  lrwxrwxrwx 1 4 Nov  8  2014 /bin/sh -> dash
  $ /bin/sh -c 'echo --help'
  --help
  $ /bin/bash -c 'echo --help'
  --help
  $ /bin/ash -c 'echo --help'
  --help
  $ /bin/dash -c 'echo --help'
  --help
  $ /bin/ksh -c 'echo --help'
  --help
  $ /bin/csh -c 'echo --help'
  --help

I think this might be a problem that is purely academic as it can't
ever actually be hit in real life.  However if you provide an actual
example that would go a long way to making this problem clear.

> There doesn't seem to be a way to get /bin/echo to output the string "--help"

Woe is me for suggesting using -e or -E as they are terribly
non-portable options.  Don't use them!  Use printf instead.  But
having said that...

  $ /bin/echo -e --help
  --help
  $ /bin/echo -E --help
  --help

But please don't do it.  Use printf instead.  The shell printf command
has a standard syntax and may portably be used.

Bob

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