Re: Detect unset variables in gnu make

[Eric Melski]

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