    % scons -Q hello
    cc -o version.o -c version.c
    cc -o hello.o -c hello.c
    cc -o hello version.o hello.o
    % sleep 1
    % scons -Q hello
    cc -o version.o -c version.c
    scons: `hello' is up to date.
    % sleep 1
    %     [CHANGE THE CONTENTS OF hello.c]
    % scons -Q hello
    cc -o version.o -c version.c
    cc -o hello.o -c hello.c
    cc -o hello version.o hello.o
    % sleep 1
    % scons -Q hello
    cc -o version.o -c version.c
    scons: `hello' is up to date.