Re: Another new 4.0 feature? functions can't return '1', (()) can't eval to 0?

[Linda Walsh]

Chet Ramey wrote:
> On 8/8/11 11:43 PM, Linda Walsh wrote:
> > I have a function that returns true/false.
> >
> > during development, (and sometimes thereafter depending on the script, I
> > run with -eu, to make sure the script stops as soon as there is a
> > problem (well, to 'try' to make sure, many are caught.
> >
> > But there are two instances that cause an error exit that seem pretty
> > unuseful and I don't remember them breaking this way before.
>
> The change to make (( honor the `errexit' option came in with bash-4.1,
> part of the cleanup after the Posix changes to the specification of the
> behavior of `set -e'.  Most of the other changes in this area came in
> with bash-4.0.
----
        I thought (()) was a bash extension?

        If so, why shoe-horn it into a 20y/o spec**?  It's often used for
doing calculations -- that's why it was added... it can only be used
where a command can be used, so having it die whenever it evals to 0 -- just
doesn't make sense.  If there's an error in the calculation, like division
by zero, sure, but just because I come up with a result of 0, == it's a far
stretch to think that would be an error.


((sec=1,min=60*sec,hour=60*min,day=24*hour,year=365*day))
((testval=year-365*day))   ; script dies due to it being considered an 
error?

Did you get bitten by some POSIX virus?




> Posix changed set -e to cause the shell to exit when any command fails,
> not just when simple commands fail, as in versions of the standard up
> to and including Posix.1-2008.
---
(()) isn't a command, it's a calculation (how's that for different 
justification?)


>  There are the usual exceptions (command
> following if, commands preceding && and ||, and so on).  This was
> changed for better alignment with historical versions of the shell and
> to reconcile differences between implementations.
>
>
> > 2)  a function returning a false value  -- Tried putting the ((expr)) in
> > an if:
> >
> > if ((expr)); then return 0; else return 1;
> >
> > As soon as it sees the return 1, it exits, -- as I returned 'false'
> > (error).
----
        It was followed by an &&, has that changed too?

        i.e. must it be followed by an '||' (so the entire expression
comes out as 'true'?)


> This should have always been the case -- a function is a simple command,
> so its returning a non-zero exit status should cause the shell to exit.
> This was true even before Posix changed.
----
        No wonder I'm going crazy....a bunch of changes went in that really
hurt functionality.

** -- wait, I thought posix was dead ages ago....there are updates? 
2008?  is that
the latest?   #*(@#$()@#)!@)*&%   they whole reason for the standard was 
so programs
wouldn't keep breaking...and now they change the standards...

wonderful...
seems like that eliminates the justification for having a standard -- 
other than to force
everyone to rewrite and update to a new standard...hmmm....