Re: s6-log can create current with 640?

[Jonathan de Boyne Pollard <J.deBoynePollard-newsgroups@NTLWorld.COM>]

Laurent Bercot:
> The real question is, why is there a "umask" binary that's not the one 
> from execline? Non-chainloading non-builtin umask is nonsense, just 
> like non-chainloading non-builtin cd. 

Not quite.  People find uses for these things, and as the SUS rationale 
points out, for every potentially useless external equivalent of a 
(non-special) built-in command someone has come up with an arcane actual 
use for it.  Even "cd".

* 
https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap01.html#tag_23_01_07

* https://unix.stackexchange.com/q/50058/5132

The POSIX model is therefore that all non-special built-ins are also 
available as executables; or, rather, that all of the standard utilities 
that are not special built-ins are simply *available* (via execvp(), 
find -exec, env, and *all of the other* ways that standard utilities can 
be invoked), and whether they are built-in or not, to a shell or 
otherwise, is an implementation detail as far as actually invoking the 
utility is concerned.  (Very few shells truly conform to this, but the 
Watanabe shell largely does in its non-native mode.)

* https://unix.stackexchange.com/q/347188/5132

* https://unix.stackexchange.com/q/496259/5132

nosh, not being a shell, is not bound by this.  Its built-ins are found 
before a PATH search is enacted.  So it actually does what M. Geraghty 
mistakenly thought execline was doing.  It finds its own built-ins in 
preference to finding external commands; so invoking "umask" (without 
directory name prefix) within a nosh script will always invoke the 
built-in chain-loading one, irrespective of PATH. (Several of the 
non-conformant shells do this, too, giving their built-ins unequivocal 
precedence over a PATH search.  Some even document this behaviour.  But 
it is not standard-conformant for a shell.)

* https://unix.stackexchange.com/a/496377/5132

* http://jdebp.uk./Softwares/nosh/guide/commands/exec.xml

execline always searches PATH.  It does not have built-ins like nosh or 
shells, in the first place.  There's a quirk about when changes to PATH 
take effect, and it does not quite have the POSIX semantics for when 
PATH is not set, but other than that it actually has the POSIX model 
behaviour: Commands are located using PATH, and what command one invokes 
by the name "umask" is entirely determined by what PATH lists.

* https://unix.stackexchange.com/a/448799/5132