Re: porter's handbook documentation on avoiding != variable assignments

[Matthew Seaman]

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


.if !make(describe)
VARIABLE!= whatever
.endif

        Cheers,

        Matthew

--
Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                 Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                 Kent, CT11 9PW

or

signature.asc
Description: OpenPGP digital signature