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

From: Chet Ramey
Subject: Re: Another new 4.0 feature? functions can't return '1', (()) can't eval to 0?
Date: Tue, 09 Aug 2011 19:42:05 -0400
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv: Gecko/20110616 Lightning/1.0b2 Thunderbird/3.1.11

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.

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.  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).

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.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/

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