RE: Detect unset variables in gnu make

[Rakesh Sharma]

Hello Eric,

Your suggestion to use the function $(file ...) worked for me! This function 
appears new in 4.0 looks like.
It appeared to me that the reasons $(file...) was brought forth is to end the 
misery of the new-line issues!

What I have observed in gnu make is that the variables (make variables) are 
used in 3 locations:
   Inside of other make variables or code. e.g., $(info ...$(make_var)...)
   Inside the recipe section (shell). e.g.,   echo $(make_var)
   Inside the shell but that shell is within the make code. e.g., $(shell echo 
$(make_var)...)

Maybe there might be other cases, but I am not aware of those. And what I see 
is that there's great non-uniformity in the way gnu make processes these cases, 
thereby adding to the errors.

Thanks,
Rakesh

> Date: Wed, 9 Apr 2014 12:52:50 -0700
> From: address@hidden
> To: address@hidden
> Subject: Re: Detect unset variables in gnu make
> 
> On 04/09/2014 11:40 AM, Rakesh Sharma wrote:
> > Hello Guenther,
> >
> > Thanks for the tips about the $(origin varname) function. That is solving 
> > the problems I was having. As regards the value of the variable I like to 
> > keep them in 3 domains:
> >
> > unset <- never been defined (or undefined midway)
> > null <- defined but set to an empty value (/^$/) => length($var) = 0
> > nonnull <- defined & set to a nonnull value(even if all spaces /^\s+$/ or 
> > /\S/ or better still /./)   =>  length($var) > 0
> >
> > But like you mentioned, I am coming around to the fact that null or unset 
> > variables need to be clubbed together in make.
> >
> > I am finding a great dichotomy in the way make handles newlines embedded 
> > within make variables. $(info ...$(string_with_NLs_)  outputs ok,
> > but the same string when used inside recipies (i.e., shell) creates untold 
> > misery. No amount of escaping, subst, etc. seem to help here.
> 
> Rakesh,
> 
> It can be quite tricky to use variables with embedded newlines in make. 
>   If you're using GNU make 4.0, the $(file) function may provide you a 
> solution.  Otherwise, this answer on StackOverflow may help:
> 
> http://stackoverflow.com/a/649462/77345
> 
> Best regards,
> 
> Eric Melski
> Chief Architect
> Electric Cloud, Inc.
> http://blog.melski.net
> 
> 
> 
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