However bjam gives me the following error:
witold@witold-MacBookPro:~/prog/bnb$ bjam -a
Jamroot:16: in modules.load
*** argument error
* rule path-constant ( name : value + )
* called with: ( BOOST_ROOT : )
* missing argument value
/usr/share/boost-build/build/project.jam:1007:see definition of rule 'path-constant' being called
/usr/share/boost-build/build/project.jam:314: in load-jamfile
/usr/share/boost-build/build/project.jam:62: in load
/usr/share/boost-build/build/project.jam:168: in project.find
/usr/share/boost-build/build-system.jam:569: in load
/usr/share/boost-build/kernel/modules.jam:283: in import
/usr/share/boost-build/kernel/bootstrap.jam:142: in boost-build
/usr/share/boost-build/boost-build.jam:8: in module scope