Back in 1.53.0, I could do the following:

    ./bootstrap.sh
    (cd tools/bcp; ../../b2)
    bin.v2/.../bcp build filesystem .../temp

Then in .../temp run ./bootstrap.sh and ./b2 to build just filesystem (or whatever else I copied).

In 1.54.0, the copy doesn't build:

brs% ./b2

Building the Boost C++ Libraries.


/auto/tmpfs/temp/tools/build/v2/build/targets.jam:397: in find-really
*** argument error
* rule project.is-registered-id ( id )
* called with: (  )
* missing argument id
/auto/tmpfs/temp/tools/build/v2/build/project.jam:600:see definition of rule 'project.is-registered-id' being called
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:457: in class@project-target.find
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:841: in resolve-reference
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:858: in targets.generate-from-reference
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1245: in generate-dependencies
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1302: in class@basic-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:757: in generate-really
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:729: in class@main-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:272: in class@project-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:874: in targets.generate-from-reference
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1245: in generate-dependencies
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1302: in class@basic-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:757: in generate-really
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:729: in class@main-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:874: in targets.generate-from-reference
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1245: in generate-dependencies
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1302: in alias-target-class.generate
/auto/tmpfs/temp/boostcpp.jam:391: in build-multiple
/auto/tmpfs/temp/boostcpp.jam:353: in class@top-level-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:757: in generate-really
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:729: in class@main-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:874: in targets.generate-from-reference
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1245: in generate-dependencies
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:1302: in alias-target-class.generate
/auto/tmpfs/temp/boostcpp.jam:391: in build-multiple
/auto/tmpfs/temp/boostcpp.jam:353: in class@top-level-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:757: in generate-really
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:729: in class@main-target.generate
/auto/tmpfs/temp/tools/build/v2/build/targets.jam:272: in class@project-target.generate
/auto/tmpfs/temp/tools/build/v2/build-system.jam:707: in load
/auto/tmpfs/temp/tools/build/v2/kernel/modules.jam:289: in import
/auto/tmpfs/temp/tools/build/v2/kernel/bootstrap.jam:139: in boost-build
/auto/tmpfs/temp/boost-build.jam:17: in module scope