ExtUtils::MakeMaker::prompt is the de-facto standard for prompt and Module::Build follows the convention. http://search.cpan.org/dist/Module-Build/lib/Module/Build/API.pod#prompt. If you want it to be optional, you can always

perl ....PL --promptme
if( $promptme ){
   ...prompt(...
}

# OR
if( $ENV{prompt_me_big_boy} ){
    ...prompt(...
}
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