Date: Sun, 20 Jul 2008 10:04:55 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Kris Kennaway <kris@freebsd.org> Cc: ports@freebsd.org Subject: Re: porter's handbook documentation on avoiding != variable assignments Message-ID: <4882FFB7.1090501@infracaninophile.co.uk> In-Reply-To: <488232AE.4090701@FreeBSD.org> References: <484EAFAC.3020208@FreeBSD.org> <488232AE.4090701@FreeBSD.org>
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Kris Kennaway wrote:
> Can someone add to the PH a version of the advice below? It might need=
=20
> to be fleshed out a bit to provide more context.
>=20
> Kris
>=20
>> Variable assignments with !=3D are bad! Try as hard as you can to avo=
id=20
>> using them -- especially in Mk/*! Every time something processes your=
=20
>> makefile it will spawn a command, even if it is not relevant for the=20
>> operation being performed. If you need to run shell commands, try to =
>> isolate them within a makefile target. You can avoid code duplication=
=20
>> by assigning the *shell commands* (not their output) to a variable and=
=20
>> inserting it into your code block.
>>
>> e.g. instead of
>>
>> --=20
>> VARIABLE!=3D do some shell stuff; do some other stuff
>>
>> target:
>> echo ${VARIABLE}
>> --=20
>>
>> do this (or similar):
>>
>> --=20
>> VARIABLE_CMDS=3D do some shell stuff; do some other stuff
>>
>> target:
>> echo $$(${VARIABLE_CMDS})
>> --=20
>>
>> 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=20
>> process executions.
Would it be acceptable to use something like:
=2Eif !defined(BUILDING_INDEX)
VARIABLE!=3D something or other
=2Eendif
or=20
=2Eif !make(describe)
VARIABLE!=3D whatever
=2Eendif
Cheers,
Matthew
--=20
Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
Kent, CT11 9PW
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