Managing Projects with GNU Make, 3rd Edition

Appendix A. Running make

GNU make has an impressive set of command-line options. Most command-line options include a short form and a long form. Short commands are indicated with a single dash followed by a single character, while long options begin with a double dash usually followed by whole words separated by dashes. The syntax of these commands is:

-o argument
--option-word=argument

The following are the most commonly used options to make. For a complete listing, see the GNU make manual or type make --help.

--always-make
-B

Assume every target is out of date and update them all.

--directory=directory
-C directory

Change to the given directory before searching for a makefile or performing any work. This also sets the variable CURDIR to directory.

--environment-overrides
-e

Prefer environment variables to makefile variables when there is a choice. This command-line option can be overridden in the makefile for particular variables with the override directive.

--file=makefile
-f makefile

Read the given file as the makefile rather than any of the default names (i.e., makefile, Makefile, or GNUMakefile).

--help
-h

Print a brief summary of the command-line options.

--include-dir=directory
-I directory

If an include file does not exist in the current directory, look in the indicated directories for include files before searching the compiled-in search path. Any number of --include-dir options can be given on the command line.

--keep-going
-k

Do not terminate the make process if a command returns an error status. Instead, skip the remainder of the current target, and continue on with other targets.

--just-print
-n

Display the set of commands that would be executed by make, but do not execute any commands from command scripts. This is very useful when you want to know what make will do before actually doing it. Be aware that this option does not prevent code in shell functions from executing, just commands in command scripts.

--old-file=file
-o file

Treat file as if it were infinitely old, and perform the appropriate actions to update the goals. This can be very useful if a file has been accidentally touched or to determine the effect of one prerequisite on the dependency graph. This is the complement of --new-file (-W).

--print-data-base
-p

Print make’s internal database.

--touch
-t

Execute the touch program on each out-of-date target to update its timestamp. This can be useful in bringing the files in a dependency graph up to date. For instance, editing a comment in a central header file may cause make to unnecessarily recompile an immense amount of code. Instead of performing the compile and wasting machine cycles, you can use the --touch option to force all files to be up to date.

--new-file=file
-W file

Assume file is newer than any target. This can be useful in forcing an update on targets without having to edit or touch a file. This is the complement of --old-file.

--warn-undefined-variables

Print a warning message if an undefined variable is expanded. This is a useful diagnostic tool since undefined variables quietly collapse into nothing. However, it is also common to include empty variables in makefiles for customization purposes. Any unset customization variables will be reported by this option as well.