The simplest project that Boost.Build can construct is stored in example/hello/ directory. The project is described by a file called Jamroot that contains:

exe hello : hello.cpp ;

Even with this simple setup, you can do some interesting things. First of all, just invoking bjam will build the hello executable by compiling and linking hello.cpp. By default, debug variant is built. Now, to build the release variant of hello, invoke

bjam release

Note that debug and release variants are created in different directories, so you can switch between variants or even build multiple variants at once, without any unnecessary recompilation. Let's extend the example by adding another line to our project's Jamroot:

exe hello2 : hello.cpp ;

Now let us build both the debug and release variants of our project again:

bjam debug release

Note that two variants of hello2 are linked. Since we have already built both variants of hello, hello.cpp won't be recompiled; instead the existing object files will just be linked into the corresponding variants of hello2. Now let's remove all the built products:

bjam --clean debug release

It's also possible to build or clean specific targets. The following two commands, respectively, build or clean only the debug version of hello2.

bjam hello2
bjam --clean hello2