Re: [Help-bash] Undocumented caret logical operator?

[Eric Blake]

On 05/02/2018 01:06 PM, Greg Wooledge wrote:
> On Wed, May 02, 2018 at 01:51:42PM -0400, G. Branden Robinson wrote:
> > The experiments show that it is not acting as an
> > "undocumented synonym for |" (bashref re: SVR4.2's Bourne shell)
>
> > echo -n expect TRUE:
> > true ^ false && echo TRUE || echo FALSE
>
> Outside of legacy Bourne shells, the ^ is just a character with no
> special meaning, like x or % or 8.  Here (above), you're passing two
> extra arguments to the "true" command, which simply ignores them.

And for more historical trivia, the reason POSIX standardized:

case a in [!b]) echo yes;; esac

and NOT

case a in [^b]) echo yes;; esac

(although the latter is permitted as an extension, and bash implements 
that extension), is BECAUSE of the legacy shells where ^ was an operator 
and had to be quoted, such that quoting made it harder to use in negated 
group globs (when compared to the usual spelling of negated groups in 
regular expressions), while ! did not need quoting.

On a distant tangent, Microsoft's cmd still uses ^-newline as a line 
continuation escape (although cmd and sh are so radically different that 
it's unusual to even attempt to write a file that would perform in a 
sane manner under both shells).

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org