Date: Sun, 20 Jul 2008 12:49:30 +0200 From: Kris Kennaway <kris@FreeBSD.org> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: ports@freebsd.org Subject: Re: porter's handbook documentation on avoiding != variable assignments Message-ID: <4883183A.7090100@FreeBSD.org> In-Reply-To: <4882FFB7.1090501@infracaninophile.co.uk> References: <484EAFAC.3020208@FreeBSD.org> <488232AE.4090701@FreeBSD.org> <4882FFB7.1090501@infracaninophile.co.uk>
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Matthew Seaman wrote:
> Kris Kennaway wrote:
>> Can someone add to the PH a version of the advice below? It might
>> need to be fleshed out a bit to provide more context.
>>
>> Kris
>>
>>> Variable assignments with != are bad! Try as hard as you can to
>>> avoid using them -- especially in Mk/*! Every time something
>>> processes your makefile it will spawn a command, even if it is not
>>> relevant for the operation being performed. If you need to run shell
>>> commands, try to isolate them within a makefile target. You can
>>> avoid code duplication by assigning the *shell commands* (not their
>>> output) to a variable and inserting it into your code block.
>>>
>>> e.g. instead of
>>>
>>> --
>>> VARIABLE!= do some shell stuff; do some other stuff
>>>
>>> target:
>>> echo ${VARIABLE}
>>> --
>>>
>>> do this (or similar):
>>>
>>> --
>>> VARIABLE_CMDS= do some shell stuff; do some other stuff
>>>
>>> target:
>>> echo $$(${VARIABLE_CMDS})
>>> --
>>>
>>> This defers the command execution to the point where the target runs,
>>> so in the case when the target is *not* run (e.g. during INDEX builds or
>>> other recursive port traversals), then you avoid wasting one or more
>>> process executions.
>
> Would it be acceptable to use something like:
>
> .if !defined(BUILDING_INDEX)
> VARIABLE!= something or other
> .endif
>
> or
> .if !make(describe)
> VARIABLE!= whatever
> .endif
No because that only avoids one particular case, not the default case :)
Kris
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