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A package is a standard OS (e.g. Linux) library that is linked with an EPICS application. An example is boost or an XML parsing library.
Your top level directory must have a Makefile.
DIRS defines which directories should be entered. Each directory should have a Makefile which is read by make.
<dir_name>_DEPEND_DIRS I'm not sure what this is.
If you're building an app (not a module, not a library), your app will have a Makefile in its src directory.
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