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From: Greg Wooledge <wooledg@eeg.ccf.org>
Newsgroups: gnu.bash.bug
Subject: Re: Assignment-like word shouldn't be subjected to tilde expansion in POSIX mode
Date: Tue, 21 Jul 2020 08:30:05 -0400
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On Tue, Jul 21, 2020 at 03:14:59PM +0300, M. Nejat AYDIN wrote:
> On 7/21/20 2:48 PM, Greg Wooledge wrote:
> > On Tue, Jul 21, 2020 at 10:55:06AM +0300, M. Nejat AYDIN wrote:
> > > Also, shouldn't the tilde be expanded following
> > >      $ echo ~:
> > > ? The colon terminates tilde-prefix in an assignment, but there is no
> > > assignment involved here.
> > 
> > Works for me.
> > 
> > unicorn:~$ echo ~:
> > /home/greg:
> > 
> > Also in POSIX mode.
> > 
> 
> Oops, I've misstated.
> I think the tilde in
>     $ echo ~:
> shouldn't have been expanded and should have been printed verbatim:
>     ~:

Tilde Expansion, according to POSIX:

  A "tilde-prefix" consists of an unquoted <tilde> character at the
  beginning of a word, followed by all of the characters preceding the
  first unquoted <slash> in the word, or all the characters in the word if
  there is no <slash>. In an assignment (see XBD Variable Assignment),
  multiple tilde-prefixes can be used: at the beginning of the word
  (that is, following the <equals-sign> of the assignment), following
  any unquoted <colon>, or both. A tilde-prefix in an assignment is
  terminated by the first unquoted <colon> or <slash>. If none of the
  characters in the tilde-prefix are quoted, the characters in the
  tilde-prefix following the <tilde> are treated as a possible login
  name from the user database. [...]
  If the system does not recognize the login name, the results are
  undefined.

For the record, ksh does the same as bash.  Dash leaves the tilde
unexpanded.  Obviously, I am assuming that one does not have a user
named : (as that would be basically impossible on any unix that uses
an /etc/passwd file in the traditional format).

I have no objection to bash's decision here.  I actually find it less
surprising than dash's decision, although both are rational ones.