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Re: [coreutils] Re: Builds of coreutils-8.6.19-1369f

From: Jim Meyering
Subject: Re: [coreutils] Re: Builds of coreutils-8.6.19-1369f
Date: Sat, 06 Nov 2010 17:02:28 +0100

Eric Blake wrote:
> On 11/06/2010 08:19 AM, Jim Meyering wrote:
>> Andreas Schwab wrote:
>>> Jim Meyering <address@hidden> writes:
>>>> Here's a better test case:
>>>>     $ /bin/sh -c 'f(){ local s=$IFS; test -n "$s"; }; f'
>>>>     [Exit 1]
>>>> And based on that, here's a patch to gnulib's tests/
>>>> that solves the problem more generally:
>>>> (but this is not enough for coreutils, since some
>>>> failing tests don't yet use
>>> Why not just add the quotes?  This isn't formally an assignment, so the
>>> behaviour of the shell is reasonable after all.
>> Actually, I'm doing both for the upcoming release.
>> Adding the quotes as a stop-gap measure, because it feels like a
>> kludge.  I'll remove it once I've converted all tests to use
>> IMHO, the fact that VAR=$OTHER_VAL never needs quotes
>> should imply that `local VAR=$OTHER_VAL' also requires no quotes.
> Local is not required by POSIX.

Yes, that is unfortunate.
However, without it, we end up perpetrating unspeakable
crimes upon variable names -- or violating user name-spaces,
or simply writing uglier code than we could have with "local".

As to whether all users of can deal with this additional
constraint, I have my doubts, and hence I have not pushed the
change to the gnulib repository.  It may make sense to allow
that shell-selection snippet to be customized via some new
separate file, say init.early, that would be sourced early on.

> If local is a normal application, then
> it requires quotes.  Only shells that provide it as a special builtin,
> like bash, can support 'local s=$IFS' without needing the quotes.
> By the way, if you insist on having 'local', even though it is not
> POSIX, you could at least work around the BSD shell issue by:
> local s
> s=$IFS

Thanks, but while that would be good enough for now,
there's no telling whether a similar use appearing
a few months from now would be caught in review.

Requiring a sensible shell -- thus relieving us of the burden of
remembering yet another portability quirk -- is one of my favorite
flavors of defensive programming.

> rather than joining the assignment in the same expression as the
> declaration.  This is a good habit to get into anyways, since:
> local s=$(false); echo $?
> 0
> local t; t=$(false); echo $?
> 1
> that is, local is an expression of its own, and succeeds if the
> assignment completed, throwing out the status of any command
> substitutions used to compute that value; while doing assignment on its
> own line has nothing to override the command substitution value.

Thanks!  I didn't know about that one, and in fact had a few
(mis)uses matching just that pattern in my shell startup files:

    local rev=$(< $pv) || return 1

Rewrote it as you'd expect, now:

    local rev
    rev=$(< $pv) || return 1

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