When reiteratively developing a master m4-style build configuration file, it is often necessary to clear out the current obj directory and start afresh. The -c switch does just that:

% ./Build -c
...
Clearing out existing obj.SunOS.4.1.4.sun4 tree

When combined with the -f switch (-E) the directory is first cleared, then a new directory is configured, and sendmail is built.

Note that it is mandatory that you run Build with the -c switch immediately after you modify your m4 build file. If you don't, your changes in that m4 build file will have no effect. The m4 build file is used to create a new Makefile, and the Makefile is what actually builds the program.

Note that the fresh Makefile target is a synonym for this switch. That is, you can also do this:

% make fresh