SConscript files make it easy to create a build
hierarchy because all of the file and directory names
in a subsidiary
SConscript files are interpreted
relative to the directory in which that
SConscript file lives.
Typically, this allows the
SConscript file containing the
instructions to build a target file
to live in the same directory as the source files
from which the target will be built,
making it easy to update how the software is built
whenever files are added or deleted
(or other changes are made).
It also tends to keep scripts more readable as they don't
need to be filled with complex paths.
For example, suppose we want to build two programs
prog2 in two separate directories
with the same names as the programs.
One typical way to do this would be
with a top-level
SConstruct file like this:
SConscript files that look like this:
env = Environment() env.Program('prog1', ['main.c', 'foo1.c', 'foo2.c'])
env = Environment() env.Program('prog2', ['main.c', 'bar1.c', 'bar2.c'])
Then, when we run SCons in the top-level directory, our build looks like:
scons -Qcc -o prog1/foo1.o -c prog1/foo1.c cc -o prog1/foo2.o -c prog1/foo2.c cc -o prog1/main.o -c prog1/main.c cc -o prog1/prog1 prog1/main.o prog1/foo1.o prog1/foo2.o cc -o prog2/bar1.o -c prog2/bar1.c cc -o prog2/bar2.o -c prog2/bar2.c cc -o prog2/main.o -c prog2/main.c cc -o prog2/prog2 prog2/main.o prog2/bar1.o prog2/bar2.o
Notice the following:
First, you can have files with the same names
in multiple directories, like
in the above example.
Second, when building,
SCons stays in the top-level directory
SConstruct file lives)
and issues commands that use the path names
from the top-level directory to the
target and source files within the hierarchy.
This works because SCons reads all the SConscript files
in one pass, interpreting each in its local context,
building up a tree of information, before starting to
execute the needed builds in a second pass.
This is quite different than some other build tools
which implement a heirarcical build by recursing.