The include dependences shown in Figure 1.1 cannot be created by make itself. An additional external executable is required to perform this analysis. Some C compilers have this functionality to output include file dependences by using appropriate options. If not available from the compiler, a shell script makedepend analyzing the C preprocessor output can be used. In both cases the makefile itself is modified and the make utility itself is working on an outdated version unless it is restarted or a recursive invocation is used. The dependences generated by the external command are appended at the end of the makefile so that these are known with the next invocation of the tool. It is not possible to put the information back into a running make.