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From: Bart Schaefer <schaefer@brasslantern.com>
Date: Fri, 29 Dec 2017 17:14:38 -0800
Message-ID: <CAH+w=7bB+FugYxHnw-6WWLYU3DoCxv_FangQiDcRWN=LR+Hvig@mail.gmail.com>
Subject: Re: How should empty aliases work?
To: Zsh hackers list <zsh-workers@zsh.org>
Content-Type: text/plain; charset="UTF-8"

On Fri, Dec 29, 2017 at 12:30 AM, Bart Schaefer
<schaefer@brasslantern.com> wrote:
>
> % alias empty=''
> % alias output='empty echo'
> % alias echo='print -r bar'
> % output foo
>
> What actually happens is that "echo" expands and "print -r bar foo" is
> executed.  If that's correct, can someone explain why?

I think the answer is that being a word in command position has
precedence over being a word preceded by an alias replacement.  Words
in command position are always alias-replaceable; words not in command
position are alias-replaceable if preceded by an alias replacement
that ended with a space.

So when "empty" disappears, it leaves "echo" in command position and
the first clause applies even though the second clause does not.