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2.1 Introducing the GNU Build System

It is a truth universally acknowledged, that as a developer in possession of a new package, you must be in want of a build system.

In the Unix world, such a build system is traditionally achieved using the command make (see Overview in The GNU Make Manual). You express the recipe to build your package in a ‘Makefile’. This file is a set of rules to build the files in the package. For instance the program ‘prog’ may be built by running the linker on the files ‘main.o’, ‘foo.o’, and ‘bar.o’; the file ‘main.o’ may be built by running the compiler on ‘main.c’; etc. Each time make is run, it reads ‘Makefile’, checks the existence and modification time of the files mentioned, decides what files need to be built (or rebuilt), and runs the associated commands.

When a package needs to be built on a different platform than the one it was developed on, its ‘Makefile’ usually needs to be adjusted. For instance the compiler may have another name or require more options. In 1991, David J. MacKenzie got tired of customizing ‘Makefile’ for the 20 platforms he had to deal with. Instead, he handcrafted a little shell script called ‘configure’ to automatically adjust the ‘Makefile’ (see Genesis in The Autoconf Manual). Compiling his package was now as simple as running ./configure && make.

Today this process has been standardized in the GNU project. The GNU Coding Standards (see The Release Process in The GNU Coding Standards) explains how each package of the GNU project should have a ‘configure’ script, and the minimal interface it should have. The ‘Makefile’ too should follow some established conventions. The result? A unified build system that makes all packages almost indistinguishable by the installer. In its simplest scenario, all the installer has to do is to unpack the package, run ./configure && make && make install, and repeat with the next package to install.

We call this build system the GNU Build System, since it was grown out of the GNU project. However it is used by a vast number of other packages: following any existing convention has its advantages.

The Autotools are tools that will create a GNU Build System for your package. Autoconf mostly focuses on ‘configure’ and Automake on ‘Makefile’s. It is entirely possible to create a GNU Build System without the help of these tools. However it is rather burdensome and error-prone. We will discuss this again after some illustration of the GNU Build System in action.

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