Re: [BUG]builtin echo error doing arguments parsing

[Stephane Chazelas <stephane.chazelas@xxxxxxxxx>]

2018-02-22 19:34:23 +0000, Peter Stephenson:
> On Thu, 22 Feb 2018 20:00:58 +0100
> Mikael Magnusson <mikachu@xxxxxxxxx> wrote:
> > I didn't try the patch but currently echo
> > -- just outputs --, only - terminates options for echo.
> 
> Yes, the -- behaviour appears to be general behaviour, in fact,
> so not something that should be changed.  So indeed it's hard to
> do this at the moment in a shell script without some kind of kludge
> for zsh.  "disable echo" and use /bin/echo might be the best bet.
> 
> However, I'm not really sure if that makes it less or actually more
> useful to align with other shells (with POSIXBUILTINS) from now on...
> it's not obvious perpetuating the need for a kludge for ever more
> is the best bet.
[...]

IMO, the best thing to do here is to do nothing. Leave it as it
is.

The fact that - marks the end of options in zsh is documented
and relatively well known.

See
https://unix.stackexchange.com/questions/65803/why-is-printf-better-than-echo

That makes it one of the very few echo implementations that can
actually output arbitrary strings reliably (the only one  if you
consider that zsh is the only shell that can store NULs in its
variables)

echo -E - $var

The only other modern implementation I'm aware of that can do
that (in a Bourne-like shell) is yash's with its:

ECHO_STYLE=raw echo "$var"

To be POSIX compliant, echo -- *must* output --<nl> (-- as an
end-of-option marker must *not* be supported), and support for
-, -e and -E should be disabled. Also echo -nn should output
-nn<nl>.

However doing that would certainly break many scripts as the sh
emulation is often used to interpret code written for bash and
bash is also not POSIX compliant in that regard even in POSIX
mode (unless the xpg_echo option is also enabled) as "echo -e"
doesn't output "-e<nl>" there.

To be UNIX compliant, no option should be recognised and -e
should be the default.

People already know or should already know that echo cannot be
used for portability/reliability. It's too late to fix it and
zsh's implementation is actually the least broken of them (for
the very reason that it supports a way to mark the end of
options)..

zsh does support the POSIX printf and the ksh print which have a
more reliable and portable API (at least when limited to the
basic usage of echo, with the caveat that print '\01234' behaves
differently in zsh than in other ksh implementations).

See also https://github.com/att/ast/issues/370 for ksh93, where
they considered changing the behaviour of echo and eventually
backed down when considering the backward compatibility risk.

Note that pdksh was another shell that skipped "-" arguments.
But the "-" didn't mark the end of options, it was a bug in the
option parsing.

-- 
Stephane