Question

Nokogiri allows for this by specifying the libraries in the install command:

gem install nokogiri -- --with-xml2-lib=/home/joe/builds/lib 
                    --with-xml2-include=/home/joe/builds/include/libxml2 
                    --with-xslt-lib=/home/joe/builds/lib 
                    --with-xslt-include=/home/joe/builds/include

I did a little digging through Nokogiri’s source to try to find out how they allow for those options to get passed down from the command to the actual build/installation.

I noticed the use of Rake::ExtensionTask as well as mini_portile, however their use seems to be limited to cross compiling on Windows systems in their code.

Is there some bit of code I can throw in my gem to allow users to specify the library they want to link against at install time? How did nokogiri allow for this?

Answer 1

This is using the dir_config method of the mkmf library.

The gem install command uses any arguments after -- as arguments to the build command, so they get passes to your extconf.rb.

Note you still need to use have_library or find_library in order to actually link to the library.