Re: how to filter-out a word sequence?

[David Boyce]

Very helpful ideas - thanks to all 3 of you. I had not known, or 
remembered anyway, that $(subst) operates on a string rather than a 
list of whitespace-separated tokens. I think I'll go with that for 
now. For completeness, and the archives, I've put a few direct 
responses inline below.

I should say up front that the -z example was just that; there may be 
other such issues down the road. I'm looking for the most general way 
to remove whitespace-containing text and so far $(subst) looks best.

At 08:56 PM 1/4/2007, Philip Guenther wrote:
> Option 1)
>    don't put a space between the -z and its argument to begin with, then use
>    $(filter-out)

This unfortunately doesn't work because the space is required (at 
least by the Sun linker). However, it gave me the idea to use 
-Wl,-z,ignore instead which has the same semantics and is viewd by 
make as one token. So this is a possibility for any flag which can be 
reduced to the -W style.

> Option 2)
>   don't put the unwanted arguments in the general variable but 
> rather keep them
>   in another variable for use with just those targets that need them

Yes, this is the "right" solution from a software engineering 
perspective. The problem here is that there's a human engineering 
aspect as well; people need to be assured that regardless of how 
flexible the underlying build technology is, they will always be able 
to slice and dice a particular command line as needed without 
infrastructure-level work. I had thought $(filter-out) was sufficient 
for this 'checklist item' until someone pointed out the -z counter-example.

> Option 3)
>    $(subst -z foo,,$(args))
>    ...but that fails if there are multiple spaces or a tab between
> the -z and 'foo'
>
> Option 4)
>    $(subst -z foo,,$(strip $(args))
>    ...but that replaces *all* internal whitespace in $(args) with 
> single spaces

Fortunately this build system is generating its Makefiles so we can 
be certain that command line formats are entirely regular.

Thanks,
David Boyce