<s>
The	O
GNU	B-Application
Autotools	I-Application
,	O
also	O
known	O
as	O
the	O
GNU	B-Application
Build	I-Application
System	I-Application
,	O
is	O
a	O
suite	O
of	O
programming	B-Application
tools	I-Application
designed	O
to	O
assist	O
in	O
making	O
source	O
code	B-Library
packages	I-Library
portable	O
to	O
many	O
Unix-like	B-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
It	O
can	O
be	O
difficult	O
to	O
make	B-Application
a	O
software	O
program	O
portable	O
:	O
the	O
C	B-Language
compiler	O
differs	O
from	O
system	O
to	O
system	O
;	O
certain	O
library	B-Library
functions	I-Library
are	O
missing	O
on	O
some	O
systems	O
;	O
header	B-Language
files	I-Language
may	O
have	O
different	O
names	O
.	O
</s>
<s>
Autotools	B-Application
is	O
designed	O
to	O
address	O
this	O
problem	O
more	O
manageably	O
.	O
</s>
<s>
Autotools	B-Application
is	O
part	O
of	O
the	O
GNU	B-Application
toolchain	I-Application
and	O
is	O
widely	O
used	O
in	O
many	O
free	B-Application
software	I-Application
and	O
open	O
source	O
packages	B-Application
.	O
</s>
<s>
Its	O
component	O
tools	O
are	O
free	B-Application
software	I-Application
,	O
licensed	O
under	O
the	O
GNU	B-License
General	I-License
Public	I-License
License	I-License
with	O
special	O
license	O
exceptions	O
permitting	O
its	O
use	O
with	O
proprietary	B-Application
software	I-Application
.	O
</s>
<s>
The	O
GNU	B-Application
Build	I-Application
System	I-Application
makes	O
it	O
possible	O
to	O
build	O
many	O
programs	O
using	O
a	O
two-step	O
process	O
:	O
configure	B-Device
followed	O
by	O
make	B-Application
.	O
</s>
<s>
Autotools	B-Application
consists	O
of	O
the	O
GNU	B-Operating_System
utility	O
programs	O
Autoconf	B-Application
,	O
Automake	B-Application
,	O
and	O
Libtool	B-Application
.	O
</s>
<s>
Other	O
related	O
tools	O
frequently	O
used	O
alongside	O
it	O
include	O
GNU	B-Operating_System
's	O
make	B-Application
program	O
,	O
GNU	B-Application
gettext	I-Application
,	O
pkg-config	B-Application
,	O
and	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
,	O
also	O
called	O
GCC	B-Application
.	O
</s>
<s>
Autoconf	B-Application
generates	O
a	O
configure	B-Device
script	I-Device
based	O
on	O
the	O
contents	O
of	O
a	O
configure.ac	O
file	O
,	O
which	O
characterizes	O
a	O
particular	O
body	O
of	O
source	O
code	O
.	O
</s>
<s>
The	O
configure	B-Device
script	I-Device
,	O
when	O
run	O
,	O
scans	O
the	O
build	O
environment	O
and	O
generates	O
a	O
subordinate	O
config.status	O
script	O
which	O
,	O
in	O
turn	O
,	O
converts	O
other	O
input	O
files	O
and	O
most	O
commonly	O
Makefile.in	O
into	O
output	O
files	O
(	O
Makefile	O
)	O
,	O
which	O
are	O
appropriate	O
for	O
that	O
build	O
environment	O
.	O
</s>
<s>
Finally	O
,	O
the	O
make	B-Application
program	O
uses	O
Makefile	O
to	O
generate	O
executable	O
programs	O
from	O
source	O
code	O
.	O
</s>
<s>
The	O
complexity	O
of	O
Autotools	B-Application
reflects	O
the	O
variety	O
of	O
circumstances	O
under	O
which	O
a	O
body	O
of	O
source	O
code	O
may	O
be	O
built	O
.	O
</s>
<s>
If	O
a	O
source	O
code	O
file	O
is	O
changed	O
then	O
it	O
suffices	O
to	O
re-run	O
make	B-Application
,	O
which	O
only	O
re-compiles	O
that	O
part	O
of	O
the	O
body	O
of	O
the	O
source	O
code	O
affected	O
by	O
the	O
change	O
.	O
</s>
<s>
If	O
a	O
.in	O
file	O
has	O
changed	O
then	O
it	O
suffices	O
to	O
re-run	O
config.status	O
and	O
make	B-Application
.	O
</s>
<s>
If	O
the	O
body	O
of	O
source	O
code	O
is	O
copied	O
to	O
another	O
computer	O
then	O
it	O
is	O
sufficient	O
to	O
re-run	O
configure	B-Device
(	O
which	O
runs	O
config.status	O
)	O
and	O
make	B-Application
.	O
</s>
<s>
(	O
For	O
this	O
reason	O
source	O
code	O
using	O
Autotools	B-Application
is	O
normally	O
distributed	O
without	O
the	O
files	O
that	O
configure	B-Device
generates	O
.	O
)	O
</s>
<s>
If	O
the	O
body	O
of	O
source	O
code	O
is	O
changed	O
more	O
fundamentally	O
,	O
then	O
configure.ac	O
and	O
the	O
.in	O
files	O
need	O
to	O
be	O
changed	O
and	O
all	O
subsequent	O
steps	O
also	O
followed	O
.	O
</s>
<s>
To	O
process	O
files	O
,	O
autoconf	B-Application
uses	O
the	O
GNU	B-Operating_System
implementation	O
of	O
the	O
m4	B-Device
macro	O
system	O
.	O
</s>
<s>
Autoconf	B-Application
comes	O
with	O
several	O
auxiliary	O
programs	O
such	O
as	O
autoheader	B-Application
,	O
which	O
is	O
used	O
to	O
help	O
manage	O
C	B-Language
header	I-Language
files	I-Language
;	O
autoscan	O
,	O
which	O
can	O
create	O
an	O
initial	O
input	O
file	O
for	O
Autoconf	B-Application
;	O
and	O
ifnames	O
,	O
which	O
can	O
list	O
C	B-Language
pre-processor	O
identifiers	O
used	O
in	O
the	O
program	O
.	O
</s>
<s>
Automake	B-Application
helps	O
to	O
create	O
portable	O
Makefiles	O
,	O
which	O
are	O
in	O
turn	O
processed	O
with	O
the	O
make	B-Application
utility	O
.	O
</s>
<s>
It	O
takes	O
its	O
input	O
as	O
Makefile.am,	O
and	O
turns	O
it	O
into	O
Makefile.in,	O
which	O
is	O
used	O
by	O
the	O
configure	B-Device
script	I-Device
to	O
generate	O
the	O
file	O
Makefile	O
output	O
.	O
</s>
<s>
It	O
also	O
performs	O
automatic	O
dependency	O
tracking	O
;	O
every	O
time	O
a	O
source	O
file	O
is	O
compiled	O
,	O
the	O
list	O
of	O
dependencies	O
(	O
e.g.	O
,	O
C	B-Language
header	I-Language
files	I-Language
)	O
is	O
recorded	O
.	O
</s>
<s>
Later	O
,	O
any	O
time	O
make	B-Application
is	O
run	O
and	O
a	O
dependency	O
appears	O
to	O
have	O
changed	O
,	O
the	O
dependent	O
files	O
will	O
be	O
rebuilt	O
.	O
</s>
<s>
Libtool	B-Application
helps	O
manage	O
the	O
creation	O
of	O
static	B-Library
and	O
dynamic	B-Application
libraries	I-Application
on	O
various	O
Unix-like	B-Operating_System
operating	I-Operating_System
systems	I-Operating_System
.	O
</s>
<s>
Libtool	B-Application
accomplishes	O
this	O
by	O
abstracting	B-Application
the	O
library-creation	O
process	O
,	O
hiding	O
differences	O
between	O
various	O
systems	O
(	O
e.g.	O
</s>
<s>
Linux	B-Application
systems	O
vs.	O
Solaris	B-Application
)	O
.	O
</s>
<s>
Autotools	B-Application
assists	O
software	O
developers	O
to	O
write	O
cross-platform	B-Operating_System
software	I-Operating_System
and	O
make	B-Application
it	O
available	O
to	O
a	O
much	O
wider	O
user	O
community	O
,	O
including	O
in	O
its	O
source	O
code	O
form	O
to	O
those	O
users	O
who	O
wish	O
to	O
build	O
the	O
software	O
themselves	O
.	O
</s>
<s>
In	O
most	O
cases	O
users	O
simply	O
run	O
the	O
supplied	O
configure	B-Device
script	I-Device
(	O
which	O
has	O
no	O
dependencies	O
other	O
than	O
the	O
presence	O
of	O
a	O
Bourne-compatible	B-Device
shell	B-Application
)	O
,	O
and	O
then	O
a	O
make	B-Application
program	O
.	O
</s>
<s>
They	O
do	O
not	O
need	O
to	O
have	O
the	O
Autotools	B-Application
themselves	O
installed	O
on	O
the	O
computer	O
.	O
</s>
<s>
It	O
can	O
be	O
used	O
both	O
for	O
building	O
native	O
programs	O
on	O
the	O
build	O
machine	O
and	O
also	O
for	O
cross-compiling	B-Application
to	O
other	O
architectures	O
.	O
</s>
<s>
Cross-compiling	B-Application
software	O
to	O
run	O
on	O
a	O
Windows	O
host	O
from	O
a	O
Linux	B-Application
or	O
other	O
Unix-like	B-Operating_System
build	B-Application
system	I-Application
is	O
also	O
possible	O
,	O
using	O
MinGW	B-Application
,	O
however	O
native	O
compilation	O
is	O
often	O
desirable	O
on	O
operating	O
systems	O
(	O
such	O
as	O
the	O
Microsoft	B-Application
Windows	I-Application
family	O
of	O
systems	O
)	O
that	O
cannot	O
run	O
Bourne	B-Device
shell	I-Device
scripts	O
on	O
their	O
own	O
.	O
</s>
<s>
This	O
makes	O
building	O
such	O
software	O
on	O
the	O
Windows	B-Application
operating	I-Application
system	I-Application
a	O
bit	O
harder	O
than	O
on	O
a	O
Unix-like	B-Operating_System
system	I-Operating_System
which	O
provides	O
the	B-Device
Bourne	I-Device
shell	I-Device
as	O
a	O
standard	O
component	O
.	O
</s>
<s>
One	O
can	O
install	O
the	O
Cygwin	B-Language
or	O
MSYS	B-Application
system	O
on	O
top	O
of	O
Windows	O
to	O
provide	O
a	O
Unix-like	B-Operating_System
compatibility	B-General_Concept
layer	I-General_Concept
,	O
though	O
,	O
allowing	O
configure	B-Device
scripts	I-Device
to	O
run	O
.	O
</s>
<s>
Cygwin	B-Language
also	O
provides	O
the	O
GNU	B-Application
Compiler	I-Application
Collection	I-Application
,	O
GNU	B-Operating_System
make	B-Application
,	O
and	O
other	O
software	O
that	O
provides	O
a	O
nearly	O
complete	O
Unix-like	B-Operating_System
system	I-Operating_System
within	O
Windows	O
;	O
MSYS	B-Application
also	O
provides	O
GNU	B-Operating_System
make	B-Application
and	O
other	O
tools	O
designed	O
to	O
work	O
with	O
the	O
MinGW	B-Application
version	O
of	O
GCC	B-Application
.	O
</s>
<s>
Although	O
the	O
developer	O
is	O
expected	O
to	O
provide	O
a	O
configure	B-Device
script	I-Device
for	O
the	O
end-user	O
,	O
occasionally	O
the	O
user	O
may	O
wish	O
to	O
re-generate	O
the	O
configure	B-Device
script	I-Device
itself	O
.	O
</s>
<s>
Such	O
users	O
would	O
need	O
to	O
have	O
Autotools	B-Application
installed	O
,	O
and	O
to	O
use	O
components	O
such	O
as	O
its	O
autoreconf	O
.	O
</s>
<s>
The	O
autoconf-generated	O
configure	B-Device
can	O
be	O
slow	O
because	O
it	O
executes	O
programs	O
such	O
as	O
a	O
C	B-Language
compiler	O
many	O
times	O
in	O
order	O
to	O
test	O
whether	O
various	O
libraries	B-Library
,	O
header	B-Language
files	I-Language
,	O
and	O
language	O
features	O
are	O
present	O
.	O
</s>
<s>
This	O
particularly	O
affects	O
Cygwin	B-Language
,	O
which	O
,	O
due	O
to	O
its	O
lack	O
of	O
a	O
native	O
fork	B-Language
system	I-Language
call	I-Language
,	O
may	O
execute	O
configure	B-Device
scripts	I-Device
considerably	O
slower	O
than	O
Linux	B-Application
.	O
</s>
<s>
In	O
his	O
column	O
for	O
ACM	O
Queue	O
,	O
FreeBSD	B-Operating_System
developer	O
Poul-Henning	O
Kamp	O
criticized	O
the	O
GNU	B-Application
Build	I-Application
System	I-Application
:	O
</s>
<s>
Kamp	O
sketches	O
the	O
history	O
of	O
the	O
build	B-Application
system	I-Application
in	O
the	O
portability	O
problems	O
inherent	O
in	O
the	O
multitude	O
of	O
1980s	O
Unix	O
variants	O
,	O
and	O
bemoans	O
the	O
need	O
for	O
such	O
build	B-Application
systems	I-Application
to	O
exist	O
:	O
</s>
<s>
Although	O
critics	O
of	O
the	O
Autotools	B-Application
frequently	O
advocate	O
for	O
alternatives	O
that	O
provide	O
greater	O
simplicity	O
to	O
their	O
users	O
,	O
some	O
have	O
argued	O
that	O
this	O
is	O
not	O
necessarily	O
a	O
good	O
thing	O
.	O
</s>
<s>
John	O
Calcote	O
,	O
author	O
of	O
the	O
Autotools	B-Application
,	O
2nd	O
Edition	O
:	O
A	O
Practitioner	O
's	O
Guide	O
to	O
GNU	B-Application
Autoconf	I-Application
,	O
Automake	B-Application
,	O
and	O
Libtool	B-Application
,	O
opined	O
:	O
</s>
