View source for Autoconf

{{Short description|Automatic configure script builder}}
{{Distinguish|Autoconfig}}
{{Infobox software
| name                   = Autoconf
| title                  =
| logo                   = Heckert GNU white.svg
| logo size              = 100px
| screenshot             = <!-- [[File: ]] -->
| caption                =
| collapsible            =
| author                 = David Mackenzie
| developer              = [[GNU Project]]
| released               = 1991<!-- {{Start date|YYYY|MM|DD|df=yes/no}} -->
| discontinued           =
| latest release version = {{wikidata|property|preferred|references|edit|P348|P548=Q2804309}}
| latest release date    = {{Start date and age|{{wikidata|qualifier|preferred|single|P348|P548=Q2804309|P577}}|df=yes}}
| latest preview version =
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| programming language   = [[Perl]]
| operating system       = [[Cross-platform]]
| platform               =
| size                   =
| language               =
| status                 =
| genre                  = [[Programming tool]]
| license                = [[GNU General Public License|GNU GPL]]
| website                = {{URL|https://www.gnu.org/software/autoconf/}}
}}
'''GNU Autoconf''' is a tool for producing [[configure script]]s for building, installing, and packaging software on computer systems where a [[Bourne shell]] is available.
Autoconf is agnostic about the programming languages used, but it is often used for projects using [[C (programming language)|C]], [[C++]], [[Fortran]], Fortran 77, [[Erlang (programming language)|Erlang]], or [[Objective-C]].
A configure script configures a software package for [[installation (computer programs)|installation]] on a particular target system.  After running a series of tests on the target system, the configure script generates [[header files]] and a [[makefile]] from templates, thus customizing the software package for the target system.  Together with [[Automake]] and [[GNU Libtool|Libtool]], Autoconf forms the [[GNU Build System]], which comprises several other tools, notably Autoheader.
== Usage overview ==
[[File:Autoconf-automake-process.svg|thumb|450px|right|Flow diagram of Autoconf and [[Automake]]. Note that "configure.ac" was named "configure.in" in early versions of Autoconf.]]
The developer specifies the desired behaviour of the configure script by writing a list of instructions in the [[GNU m4]] language in a file called "configure.ac".  A library of pre-defined m4 [[macro (computer science)|macros]] is available to describe common configure script instructions.  Autoconf transforms the instructions in "configure.ac" into a portable configure script.
The system that will be doing the building need not have Autoconf installed: Autoconf is needed only to build the configure script, that is usually shipped with the software.
== History ==
Autoconf was begun in the summer of 1991 by David Mackenzie to support his work at the [[Free Software Foundation]].  In the subsequent years it grew to include enhancements from a variety of authors and became the most widely used build configuration system for writing portable free or [[open-source software]].
== Approach ==
Autoconf is similar to the Metaconfig package used by [[Perl]].  The [[imake]] system formerly used by the [[X Window System]] (up to X11R6.9) is closely related, but has a different philosophy.
The Autoconf approach to [[Porting|portability]] is to test for [[feature (software design)|feature]]s, not for [[Software versioning|versions]]. For example, the native C compiler on SunOS 4 did not support [[C (programming language)|ISO C]]. However, it is possible for the user or administrator to have installed an ISO C-compliant compiler.  A pure version-based approach would not detect the presence of the ISO C compiler, but a feature-testing approach would be able to discover the ISO C compiler the user had installed. The rationale of this approach is to gain the following advantages:
* the configure script can get reasonable results on newer or unknown systems
* it allows [[system administrator|administrator]]s to customize their machines and have the configure script take advantage of the customizations
* there is no need to keep track of minute details of versions, patch numbers, etc., to figure out whether a particular feature is supported or not
Autoconf provides extensive documentation around the non-portability of many POSIX shell constructs to older shells and bugs therein. It also provides M4SH, a macro-based replacement for shell syntax.<ref>{{cite web |title=Portable Shell |url=https://www.gnu.org/software/autoconf/manual/html_node/Portable-Shell.html |website=Autoconf |access-date=20 January 2020}}</ref>
==Criticism==
There is some criticism that states that Autoconf uses dated technologies, has a lot of legacy restrictions, and complicates simple scenarios unnecessarily for the author of ''configure.ac'' scripts. In particular, often cited weak points of Autoconf are:
* General complexity of used architecture, most projects use multiple repetitions.<ref name="kde">{{cite web
|title = Why the KDE project switched to CMake -- and how
|first = Alexander
|last = Neundorf
|date = 2006-06-21
|url = https://lwn.net/Articles/188693/
}}</ref><ref name="lost-bazaar">{{cite journal
|first=Poul-Henning
|last=Kamp
|date=2012-08-15
|journal=ACM Queue
|volume=10
|issue=8
|title=A Generation Lost in the Bazaar
|pages=20–23
|doi=10.1145/2346916.2349257
|s2cid=11656592
|doi-access=free
}}</ref>
* Some people think that 'configure' scripts generated by Autoconf provide only manual-driven command-line interface without any standardization.<ref name="stop-insanity"/> While it is true that some developers do not respect common conventions, such conventions do exist and are widely used.<ref name="gnu-coding">{{cite web
|title = GNU Coding Standards
|url = https://www.gnu.org/prep/standards/standards.html
}}</ref>
* m4 is unusual and unknown to many developers. Developers will need to learn it to extend Autoconf with non-standard checks.<ref name="stop-insanity">{{cite web
|first = Andrew
|last = McCall
|title = Stop the autoconf insanity! Why we need a new build system
|url = http://freshmeat.net/articles/stop-the-autoconf-insanity-why-we-need-a-new-build-system
|date = 2003-06-21
}}</ref><ref name="autocrap">{{cite web
|title        = Did you call them ''autocrap'' tools?
|first        = Poul-Henning
|last         = Kamp
|date         = 2010-04-20
|url          = https://varnish-cache.org/docs/5.0/phk/autocrap.html
|access-date  = 2017-08-16
|archive-url  = https://web.archive.org/web/20170911030645/http://varnish-cache.org/docs/5.0/phk/autocrap.html
|archive-date = 2017-09-11
|url-status     = dead
}}</ref>
* Weak backward and forward compatibility requires a wrapper script.<ref name="autoconf 2.13">{{cite web
|first = Thomas
|last = Dickey
|title = why i still use autoconf 2.13
|url = http://invisible-island.net/autoconf/autoconf.html
}}</ref>
* Autoconf-generated scripts are usually large and rather complex. Although they produce extensive logging, debugging them can still be difficult.
Due to these limitations, several projects that used GNU Build System switched to different build systems, such as [[CMake]] and [[SCons]].<ref name="kde"/><ref name="blender">{{Cite web |url=http://www.blender.org/development/release-logs/blender-233/build-systems/ |title=Blender.org - Build systems |access-date=2009-06-10 |archive-url=https://web.archive.org/web/20081202083359/http://www.blender.org/development/release-logs/blender-233/build-systems/ |archive-date=2008-12-02 |url-status=dead }}</ref>
==See also==
{{Portal|Free and open-source software}}
* [[CMake]] – Alternative build system
* [[Meson (software)|Meson]] – Another build system
* [[Configure script]]
* [[GNU build system]]
* [[pkg-config]] – Detecting package dependencies
==References==
{{Reflist}}
== External links ==
* {{official website}}
* [https://www.gnu.org/software/ac-archive/ GNU Autoconf macro archive]
* [http://sources.redhat.com/autobook/ ''The Goat Book'' homepage (aka the Autobook)] {{Webarchive|url=https://web.archive.org/web/20101220095404/http://sources.redhat.com/autobook/ |date=2010-12-20 }}
* [https://web.archive.org/web/20041013190022/http://www.openismus.com/documents/linux/automake/automake.shtml Using Automake and Autoconf with C++]
* [https://web.archive.org/web/20060413182543/http://www.openismus.com/documents/linux/using_libraries/using_libraries.shtml Using C/C++ libraries with Automake and Autoconf].
* [http://autotoolset.sourceforge.net Autotoolset home page]
* [https://web.archive.org/web/20140816060326/http://www.freesoftwaremagazine.com/books/autotools_a_guide_to_autoconf_automake_libtool Autotools: A practitioner's guide to Autoconf, Automake and Libtool]
* [https://autotools.info/ Autotools Mythbuster]
{{GNU}}
[[Category:Build automation]]
[[Category:Computer configuration]]
[[Category:Cross-platform free software]]
[[Category:Free computer libraries]]
[[Category:GNU Project software]]
[[de:GNU Build System#GNU Autoconf]]