- Corrected formatting error.
GNU Make is a tool which controls the generation of executables and other
non-source files of a program from the program's source files.
Make gets its knowledge of how to build your program from a file called the
makefile, which lists each of the non-source files and how to compute it from
other files. When you write a program, you should write a makefile for it, so
that it is possible to use Make to build and install the program.
Capabilities of Make
Make enables the end user to build and install your package without
knowing the details of how that is done -- because these details are
recorded in the makefile that you supply.
Make figures out automatically which files it needs to update, based on
which source files have changed. It also automatically determines the
proper order for updating files, in case one non-source file depends on
another non-source file.
As a result, if you change a few source files and then run Make, it does
not need to recompile all of your program. It updates only those
non-source files that depend directly or indirectly on the source files
that you changed.
Make is not limited to any particular language. For each non-source file
in the program, the makefile specifies the shell commands to compute it.
These shell commands can run a compiler to produce an object file, the
linker to produce an executable, ar to update a library, or TeX or
Makeinfo to format documentation.
Make is not limited to building a package. You can also use Make to
control installing or deinstalling a package, generate tags tables for
it, or anything else you want to do often enough to make it worth while
writing down how to do it.
Make Rules and Targets
A rule in the makefile tells Make how to execute a series of commands in
order to build a target file from source files. It also specifies a list of
dependencies of the target file. This list should include all files (whether
source files or other targets) which are used as inputs to the commands in
Here is what a simple rule looks like:
target: dependencies ...
When you run Make, you can specify particular targets to update; otherwise,
Make updates the first target listed in the makefile. Of course, any other
target files needed as input for generating these targets must be updated
Make uses the makefile to figure out which target files ought to be brought
up to date, and then determines which of them actually need to be updated.
If a target file is newer than all of its dependencies, then it is already up
to date, and it does not need to be regenerated. The other target files do
need to be updated, but in the right order: each target file must be
regenerated before it is used in regenerating other targets.
Advantages of GNU Make
GNU Make has many powerful features for use in makefiles, beyond what other
Make versions have. It can also regenerate, use, and then delete intermediate
files which need not be saved.
GNU Make also has a few simple features that are very convenient. For
example, the -o file option which says ``pretend that source file file has
not changed, even though it has changed.'' This is extremely useful when you
add a new macro to a header file. Most versions of Make will assume they must
therefore recompile all the source files that use the header file; but GNU
Make gives you a way to avoid the recompilation, in the case where you know
your change to the header file does not require it.
However, the most important difference between GNU Make and most versions of
Make is that GNU Make is free software.