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