Sometimes it's useful to look at the pre-substitution string that SCons uses to generate the command lines it executes. This can be done with the --debug=presub option:
% scons -Q --debug=presub Building prog.o with action: $CC -o $TARGET -c $CFLAGS $CCFLAGS $_CCOMCOM $SOURCES cc -o prog.o -c -I. prog.c Building prog with action: $SMART_LINKCOM cc -o prog prog.o