By default any executable present in this directory, or the directory named
similarily, but in the same directory as the compose file, will be automatically
executed once the build.sh script has build and/or pushed all
images. All variables starting with the prefix BUILD_ are exported to the
executables. The content of these variables will reflect exactly how the
build.sh script has behaved: for example, BUILD_BUILDER will
be the builder that will effectively be used after all checks have been
performed.
A variable called BUILD_IMAGES is also passed further to cleanup programs. The
variable contains the space-separated list of images that were built, or the
list of images that were pushed. When images were requested to be built and
pushed, only the list of pushed images will be present.