Re: Bash true/false builtings undocumented? "false" not working?

[Stefan Krusche <linux@stefan-krusche.de>]

Am Freitag 17 August 2018 schrieb Zenaan Harkness:
> On Fri, Aug 17, 2018 at 11:25:52AM +0200, tomas@tuxteam.de wrote:
> > On Fri, Aug 17, 2018 at 06:46:54PM +1000, Zenaan Harkness wrote:
> > > 1)
> > > Bash man page largely fails to document the true and false builtins
> > > AFAICT, except for this sentence just under the heading
> > > "^SHELL BUILTIN COMMANDS":
> > >
> > >  The :, true, false, and test builtins do not accept options and do
> > >  not treat -- specially.
> > >
> > > But whilst the subsequent list of Bash builtin commands DOES include
> > > entries for ":" (the very first entry) and "test", it appears to fail
> > > to include entries for "true" and for "false".
> > >
> > > This would not matter so much except for the following:
> > >
> > >
> > > 2)
> > > Why is executing "false" prior to testing it's output, apparently
> > > differen to executing "false" in a pipeline, e.g.:
> > >
> > > $ false
> > > $ test $? && echo ok || echo error $?
> > > ok
> > > $ false blah
> > > $ test $? && echo ok || echo error $?
> > > ok
> >
> > Note that after false,
> >
> >   test $? && echo ok || echo error $?
> >
> > expands (after variable expansion) to
> >
> >   test 0 && echo ok || echo error 0
> >
> > ... which ends up saying "ok", because test 0 succeeds :-)
> > The only one-arg test which fails is test "".
> > Yes, a bit unexpected, due to (a) the shell's evaluation model
> > and (b) test's behaviour.
> >
> > To defend bash's documenters (a bit) its help system provides you
> > with tiny snippets of information (try "help false").
>
> $ help false
> false: false
>     Return an unsuccessful result.
>
>     Exit Status:
>     Always fails.
>
>
> That accords with my previous understanding, that the exist status of
> running false gives something other than "success" (i.e. zero) - what
> am I missing?

Nothing. What Tomás wrote is false (has exit code "1" ;-)

This:

  test $? && echo ok || echo error $?

does *not* expand as Tomás said to:

  test 0 && echo ok || echo error 0

but to:

  test 1 && echo ok || echo error 1

And "test 1" also succeeds, see Greg's message.

Kind regards,
Stefan