Next: , Previous: Recursion, Up: Recursion

5.7.1 How the MAKE Variable Works

Recursive make commands should always use the variable MAKE, not the explicit command name ‘make’, as shown here:

             cd subdir && $(MAKE)

The value of this variable is the file name with which make was invoked. If this file name was /bin/make, then the command executed is ‘cd subdir && /bin/make’. If you use a special version of make to run the top-level makefile, the same special version will be executed for recursive invocations. As a special feature, using the variable MAKE in the commands of a rule alters the effects of the ‘-t’ (‘--touch’), ‘-n’ (‘--just-print’), or ‘-q’ (‘--question) option. Using the MAKE variable has the same effect as using a ‘+’ character at the beginning of the command line. See Instead of Executing the Commands. This special feature is only enabled if the MAKE variable appears directly in the command script: it does not apply if the MAKE variable is referenced through expansion of another variable. In the latter case you must use the ‘+’ token to get these special effects.

Consider the command ‘make -t’ in the above example. (The ‘-t’ option marks targets as up to date without actually running any commands; see Instead of Execution.) Following the usual definition of ‘-t’, a ‘make -t’ command in the example would create a file named subsystem and do nothing else. What you really want it to do is run ‘cd subdir && make -t’; but that would require executing the command, and ‘-t’ says not to execute commands. The special feature makes this do what you want: whenever a command line of a rule contains the variable MAKE, the flags ‘-t’, ‘-n’ and ‘-q’ do not apply to that line. Command lines containing MAKE are executed normally despite the presence of a flag that causes most commands not to be run. The usual MAKEFLAGS mechanism passes the flags to the sub-make (see Communicating Options to a Sub-make), so your request to touch the files, or print the commands, is propagated to the subsystem.