bug#57129: 29.0.50; Improve behavior of conditionals in Eshell

[Eli Zaretskii]

> Cc: larsi@gnus.org, 57129@debbugs.gnu.org
> From: Jim Porter <jporterbugs@gmail.com>
> Date: Mon, 15 Aug 2022 11:30:07 -0700
> 
> >> I need to investigate this a bit further, since on GNU/Linux, I get a
> >> new temp file every time.
> > 
> > Can you tell how you create these temporary files?  Or point me to the
> > code which does that?
> 
> The temp files are created by Eshell in lisp/eshell/esh-var.el in the 
> function 'eshell-parse-variable-ref', specifically in the part starting 
> with:
> 
>    (eq (char-after) ?\<)

Ah, okay.  It's a (mis)feature of Gnulib's gen_tempname function
(which is the guts of make-temp-file) in its implementation for
MS-Windows (and maybe other platforms?): it always begins from the
same "random" characters in the file name, and only generates other
random characters if there's already a file by that name.  So if you
are careful and delete the temporary file each time after usage, and
never need more than one temporary file at the same time, you will get
the same name every call.