Re: != vs :sh (was: py-Scientific fix)

[Joerg Sonnenberger <joerg%bec.de@localhost>]

On Sun, Mar 31, 2019 at 12:16:27PM +0200, Roland Illig wrote:
> Am 28.03.2019 um 10:33 schrieb Jonathan Perkin:
> > * On 2019-03-28 at 09:22 GMT, Edgar Fuß wrote:
> >
> >>> Yes, joerg's right, :sh is preferable.
> >> Could someone please elaborate why it is?
> >
> > It defers evaluation of the command until it is used.  So with a
> > Makefile like the following:
> >
> >   UNAME_EXCLAM!= uname
> >   UNAME_CMD=     uname
> >
> >   exclam:
> >     @echo ${UNAME_EXCLAM}
> >
> >   cmd:
> >     @echo ${UNAME_CMD:sh}
> >
> > UNAME_EXCLAM will be executed for every invocation of the Makefile,
> > whereas UNAME_CMD will only be executed when the "cmd" target is
> > called.
> 
> Thank you for this explanation. After the 2019Q1 branch, pkglint will
> warn about cases like this and provide an even more detailed explanation.

I'm against a blatant warning like that. There are valid reasons for
using !=, especially when checking that it happens in the appropiate
phase.

Joerg