<s>
GNU	B-Application
Autoconf	I-Application
is	O
a	O
tool	O
for	O
producing	O
configure	B-Device
scripts	I-Device
for	O
building	O
,	O
installing	O
,	O
and	O
packaging	O
software	O
on	O
computer	O
systems	O
where	O
a	O
Bourne	B-Device
shell	I-Device
is	O
available	O
.	O
</s>
<s>
Autoconf	B-Application
is	O
agnostic	O
about	O
the	O
programming	O
languages	O
used	O
,	O
but	O
it	O
is	O
often	O
used	O
for	O
projects	O
using	O
C	B-Language
,	O
C++	B-Language
,	O
Fortran	B-Application
,	O
Fortran	B-Application
77	O
,	O
Erlang	B-Operating_System
,	O
or	O
Objective-C	B-Language
.	O
</s>
<s>
A	O
configure	B-Device
script	I-Device
configures	B-Device
a	O
software	O
package	O
for	O
installation	B-Application
on	O
a	O
particular	O
target	O
system	O
.	O
</s>
<s>
After	O
running	O
a	O
series	O
of	O
tests	O
on	O
the	O
target	O
system	O
,	O
the	O
configure	B-Device
script	I-Device
generates	O
header	B-Language
files	I-Language
and	O
a	O
makefile	O
from	O
templates	O
,	O
thus	O
customizing	O
the	O
software	O
package	O
for	O
the	O
target	O
system	O
.	O
</s>
<s>
Together	O
with	O
Automake	B-Application
and	O
Libtool	B-Application
,	O
Autoconf	B-Application
forms	O
the	O
GNU	B-Application
Build	I-Application
System	I-Application
,	O
which	O
comprises	O
several	O
other	O
tools	O
,	O
notably	O
Autoheader	B-Application
.	O
</s>
<s>
The	O
developer	O
specifies	O
the	O
desired	O
behaviour	O
of	O
the	O
configure	B-Device
script	I-Device
by	O
writing	O
a	O
list	O
of	O
instructions	O
in	O
the	O
GNU	B-Operating_System
m4	O
language	O
in	O
a	O
file	O
called	O
"	O
configure.ac	O
 "	O
.	O
</s>
<s>
A	O
library	O
of	O
pre-defined	O
m4	O
macros	O
is	O
available	O
to	O
describe	O
common	O
configure	B-Device
script	I-Device
instructions	O
.	O
</s>
<s>
Autoconf	B-Application
transforms	O
the	O
instructions	O
in	O
"	O
configure.ac	O
 "	O
into	O
a	O
portable	O
configure	B-Device
script	I-Device
.	O
</s>
<s>
The	O
system	O
that	O
will	O
be	O
doing	O
the	O
building	O
need	O
not	O
have	O
autoconf	B-Application
installed	O
:	O
autoconf	B-Application
is	O
needed	O
only	O
to	O
build	O
the	O
configure	B-Device
script	I-Device
,	O
that	O
is	O
usually	O
shipped	O
with	O
the	O
software	O
.	O
</s>
<s>
Autoconf	B-Application
was	O
begun	O
in	O
the	O
summer	O
of	O
1991	O
by	O
David	O
Mackenzie	O
to	O
support	O
his	O
work	O
at	O
the	B-Operating_System
Free	I-Operating_System
Software	I-Operating_System
Foundation	I-Operating_System
.	O
</s>
<s>
In	O
the	O
subsequent	O
years	O
it	O
grew	O
to	O
include	O
enhancements	O
from	O
a	O
variety	O
of	O
authors	O
and	O
became	O
the	O
most	O
widely	O
used	O
build	O
configuration	O
system	O
for	O
writing	O
portable	O
free	O
or	O
open-source	B-Application
software	I-Application
.	O
</s>
<s>
Autoconf	B-Application
is	O
similar	O
to	O
the	O
Metaconfig	O
package	O
used	O
by	O
Perl	B-Language
.	O
</s>
<s>
The	O
imake	B-Application
system	O
formerly	O
used	O
by	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
(	O
up	O
to	O
X11R6.9	O
)	O
is	O
closely	O
related	O
,	O
but	O
has	O
a	O
different	O
philosophy	O
.	O
</s>
<s>
The	O
Autoconf	B-Application
approach	O
to	O
portability	O
is	O
to	O
test	O
for	O
features	O
,	O
not	O
for	O
versions	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
native	O
C	B-Language
compiler	O
on	O
SunOS	O
4	O
did	O
not	O
support	O
ISO	B-Language
C	I-Language
.	O
However	O
,	O
it	O
is	O
possible	O
for	O
the	O
user	O
or	O
administrator	B-Application
to	O
have	O
installed	O
an	O
ISO	O
C-compliant	O
compiler	O
.	O
</s>
<s>
A	O
pure	O
version-based	O
approach	O
would	O
not	O
detect	O
the	O
presence	O
of	O
the	O
ISO	B-Language
C	I-Language
compiler	O
,	O
but	O
a	O
feature-testing	O
approach	O
would	O
be	O
able	O
to	O
discover	O
the	O
ISO	B-Language
C	I-Language
compiler	O
the	O
user	O
had	O
installed	O
.	O
</s>
<s>
Autoconf	B-Application
provides	O
extensive	O
documentation	O
around	O
the	O
non-portability	O
of	O
many	O
POSIX	O
shell	O
constructs	O
to	O
older	O
shells	O
and	O
bugs	O
therein	O
.	O
</s>
<s>
There	O
is	O
some	O
criticism	O
that	O
states	O
that	O
Autoconf	B-Application
uses	O
dated	O
technologies	O
,	O
has	O
a	O
lot	O
of	O
legacy	O
restrictions	O
,	O
and	O
complicates	O
simple	O
scenarios	O
unnecessarily	O
for	O
the	O
author	O
of	O
configure.ac	O
scripts	O
.	O
</s>
<s>
In	O
particular	O
,	O
often	O
cited	O
weak	O
points	O
of	O
Autoconf	B-Application
are	O
:	O
</s>
<s>
Generated	O
'	O
configure	B-Device
 '	O
is	O
written	O
in	O
Bourne	B-Device
shell	I-Device
and	O
thus	O
Makefile	O
generation	O
is	O
slow	O
.	O
</s>
<s>
Some	O
people	O
think	O
that	O
'	O
configure	B-Device
 '	O
scripts	O
generated	O
by	O
autoconf	B-Application
provide	O
only	O
manual-driven	O
command-line	O
interface	O
without	O
any	O
standardization	O
.	O
</s>
<s>
Developers	O
will	O
need	O
to	O
learn	O
it	O
to	O
extend	O
autoconf	B-Application
with	O
non-standard	O
checks	O
.	O
</s>
<s>
Autoconf-generated	O
scripts	O
are	O
usually	O
large	O
and	O
rather	O
complex	O
.	O
</s>
<s>
Due	O
to	O
these	O
limitations	O
,	O
several	O
projects	O
that	O
used	O
GNU	B-Application
Build	I-Application
System	I-Application
switched	O
to	O
different	O
build	O
systems	O
,	O
such	O
as	O
CMake	B-Language
and	O
SCons	B-Application
.	O
</s>
