--- /dev/null
+\input texinfo @c -*-texinfo-*-
+@c %**start of header
+@setfilename autoconf.info
+@settitle Autoconf
+@setchapternewpage odd
+@c %**end of header
+@c Use on instead of odd in the setchapternewpage for single-sided printing.
+
+@set EDITION 1.6
+@set VERSION 1.6
+@set UPDATED August 1993
+
+@iftex
+@finalout
+@end iftex
+
+@ifinfo
+This file documents the GNU Autoconf package for creating scripts to
+configure source code packages using templates and an @code{m4} macro
+package.
+
+Copyright (C) 1992, 1993 Free Software Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+
+@ignore
+Permission is granted to process this file through TeX and print the
+results, provided the printed document carries copying permission
+notice identical to this one except for the removal of this paragraph
+(this paragraph not being relevant to the printed manual).
+
+@end ignore
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
+@end ifinfo
+
+@titlepage
+@title Autoconf
+@subtitle Generating Automatic Configuration Scripts
+@subtitle Edition @value{EDITION}, for Autoconf version @value{VERSION}
+@subtitle @value{UPDATED}
+@author by David MacKenzie, Roland McGrath, and Noah Friedman
+
+@page
+@vskip 0pt plus 1filll
+Copyright @copyright{} 1992, 1993 Free Software Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
+@end titlepage
+
+@node Top, Introduction, , (dir)
+@comment node-name, next, previous, up
+
+@ifinfo
+This file documents the GNU Autoconf package for creating scripts to
+configure source code packages using templates and an @code{m4} macro
+package. This is edition @value{EDITION}, for Autoconf version @value{VERSION}.
+
+@end ifinfo
+
+@menu
+* Introduction:: Autoconf's purpose, strengths, and weaknesses.
+* Distributing:: Legal restrictions on Autoconf output.
+* Making configure Scripts:: How to organize and produce Autoconf scripts.
+* Specific Tests:: Macros that check for particular features.
+* General Purpose Macros:: Macros that check for kinds of features.
+* Writing Macros:: How to add your own macros to Autoconf.
+* Makefiles:: Information Autoconf uses in @file{Makefile}s.
+* Running configure Scripts:: How to use the Autoconf output.
+* Example:: Sample Autoconf input files.
+* Preprocessor Symbol Index:: Index of C preprocessor symbols defined.
+* Macro Index:: Index of Autoconf macros.
+@end menu
+
+@node Introduction, Distributing, Top, Top
+@chapter Introduction
+
+Autoconf is a tool for producing shell scripts that automatically
+configure software source code packages to adapt to many kinds of
+UNIX-like systems. The configuration scripts produced by Autoconf are
+independent of Autoconf when they are run, so their users do not need to
+have Autoconf.
+
+The configuration scripts produced by Autoconf normally require no
+manual user intervention when run; they do not even take an argument
+specifying the system type. Instead, they test for the presence of each
+feature that the software package they are for might need individually.
+(Before each check, they print a one-line message stating what they are
+checking for, so the user doesn't get too bored while waiting for the
+script to finish.) As a result, they deal well with systems that are
+hybrids or customized from the more common UNIX variants. There is no
+need to maintain files that list the features supported by each release
+of each variant of UNIX.
+
+For each software package that Autoconf is used with, it creates a
+configuration script from a template file that lists the operating
+system features that the package can use. After the shell code to
+recognize and respond to an operating system feature has been written,
+Autoconf allows it to be shared by many software packages that can
+use (or need) that feature. If it later turns out that the shell code
+needs adjustment for some reason, it needs to be changed in only one
+place; all of the the configuration scripts can be regenerated
+automatically to take advantage of the updated code.
+
+Larry Wall's Metaconfig package is similar in purpose to Autoconf, but
+is more general. The scripts it produces require manual user
+intervention, which is quite inconvenient when configuring large source
+trees.
+
+Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling,
+if some care is taken in writing them. They should avoid executing test
+programs, since test programs compiled with a cross-compiler can not be
+executed on the host system. Also, they shouldn't do anything that
+tests features of the host system instead of the target system.
+
+Autoconf imposes some restrictions on the names of macros used with
+@code{#ifdef} in C programs (@pxref{Preprocessor Symbol Index}).
+
+Autoconf requires GNU @code{m4} in order to generate the scripts. It
+uses features that some UNIX versions of @code{m4} do not have; it is
+also reported to overflow internal limits of some versions of @code{m4}.
+
+Autoconf does not work well with GNU C library releases before 1.06.
+The GNU C library contains stubs (which always return an error) for
+functions that are not available instead of omitting them from the
+library. As a result, Autoconf scripts are fooled into thinking that
+those functions are available. This problem does not exist with
+releases 1.06 and later of the GNU C library, which define C
+preprocessor macros that the Autoconf macros @code{AC_FUNC_CHECK} and
+@code{AC_REPLACE_FUNCS} test, indicating that certain functions are
+stubs (@pxref{General Tests}, for more information on checking for
+functions).
+
+@ifinfo
+Autoconf was written by David MacKenzie, with help from Franc,ois
+@end ifinfo
+@tex
+Autoconf was written by David MacKenzie, with help from Fran\c cois
+@end tex
+Pinard, Karl Berry, Richard Pixley, Ian Lance Taylor, Roland McGrath,
+and Noah Friedman. It was inspired by Brian Fox's automatic
+configuration system for BASH, by Larry Wall's Metaconfig, and by
+Richard Stallman, Richard Pixley, and John Gilmore's configuration tools
+for the GNU compiler and object file utilities.
+
+Mail suggestions and bug reports for Autoconf to
+@code{bug-gnu-utils@@prep.ai.mit.edu}. Please include the Autoconf version
+number, which you can get by running @samp{autoconf --version}.
+
+@node Distributing, Making configure Scripts, Introduction, Top
+@chapter Distributing Autoconf Output
+
+The configuration scripts that Autoconf produces are covered by the GNU
+General Public License. This is because they consist almost entirely of
+parts of Autoconf itself, rearranged somewhat, and Autoconf is
+distributed under the terms of the GPL. As applied to Autoconf,
+the GPL just means that you need to distribute @file{configure.in} along
+with @file{configure}.
+
+Programs that use Autoconf scripts to configure themselves do not
+automatically come under the GPL. Distributing an Autoconf
+configuration script as part of a program is considered to be @emph{mere
+aggregation} of that work with the Autoconf script. Such programs are
+not derivative works based on Autoconf; only their configuration scripts
+are. We still encourage software authors to distribute their work under
+terms like those of the GPL, but doing so is not required to use
+Autoconf.
+
+@node Making configure Scripts, Specific Tests, Distributing, Top
+@chapter Making @code{configure} Scripts
+
+The configuration scripts that Autoconf produces are by convention
+called @code{configure} when they are distributed. When run, they
+create several files:
+
+@itemize @bullet
+@item
+one or more @file{Makefile} files (one in each subdirectory of the
+package), from template @file{Makefile.in} files (@pxref{Makefiles});
+
+@item
+optionally, a C header file, the name of which is configurable,
+containing @code{#define} statements;
+
+@item
+a shell script called @file{config.status} that, when run, will recreate
+the current configuration parameter settings.
+@end itemize
+
+To create a @code{configure} script with Autoconf, you need to write an
+Autoconf input file and run Autoconf on it to produce the script. And,
+of course, test the resulting script.
+
+Here is a diagram showing how the files that can be used in
+configuration are produced:
+
+@example
+acgeneral.m4 \ Makefile.in \
+acspecific.m4 \ \
+autoconf* -> m4* -> configure* -> config.status* -> Makefile \
+configure.in / | | \
+ | | | | make* -> your
+ | | | | /package
+ | | config.status* -> config.h /
+configure.in \ /
+autoheader* -> - - - - - - - - - - -> config.h.in /
+acconfig.h /
+@end example
+
+@noindent
+Executables are suffixed by @samp{*}, while files appearing twice are
+linked with lines of @samp{|}.
+
+@menu
+* Writing configure.in:: What to put in an Autoconf input file.
+* Invoking autoconf:: How to create configuration scripts.
+* Invoking autoheader:: How to create configuration header files.
+@end menu
+
+@node Writing configure.in, Invoking autoconf, , Making configure Scripts
+@section Writing @file{configure.in}
+
+To produce a @code{configure} script for a software package, create a
+file called @file{configure.in} that contains invocations of the
+Autoconf macros that test the system features your package needs or can
+use. Autoconf macros already exist to check for many features; see
+@ref{Specific Tests}, for their descriptions. For most other
+features, you can use Autoconf template macros to produce custom checks;
+see @ref{General Tests}, for information about them. For especially
+tricky or specialized features, @file{configure.in} might need to
+contain some hand-crafted shell commands. @xref{Writing Macros}, for
+guidelines on writing tests from scratch.
+
+Every @file{configure.in} must begin with a call to @code{AC_INIT} and
+end with a call to @code{AC_OUTPUT} (@pxref{Setup}). Other than that,
+the order in which @file{configure.in} calls the Autoconf macros is
+generally not important, except that some macros rely on other macros
+having been called first, because they check previously set values of
+some variables to decide what to do. These macros are noted in the
+individual descriptions (@pxref{Specific Tests}).
+
+To encourage consistency, here is a suggested order for calling the
+Autoconf macros. A few macros need to be called in a different order
+from the one given here; they are noted in their individual descriptions
+(@pxref{Specific Tests}). Note that there must not be any space
+between the macro name and the open parentheses.
+
+@display
+@group
+@code{AC_INIT(@var{file})}
+checks for programs
+checks for UNIX variants that set @code{DEFS}
+checks for header files
+checks for typedefs
+checks for functions
+checks for structure members
+checks for compiler characteristics
+checks for operating system services
+other checks for UNIX variants
+@code{AC_OUTPUT(@r{[}@var{file@dots{}}@r{]})}
+@end group
+@end display
+
+You can include comments in @file{configure.in} files by starting them
+with the @code{m4} predefined macro @code{dnl}, which discards text up
+through the next newline. These comments do not appear in the generated
+@code{configure} scripts. For example, it is helpful to begin
+@file{configure.in} files with a line like this:
+
+@example
+dnl Process this file with autoconf to produce a configure script.
+@end example
+
+@xref{Sample configure.in}, for an example of a real @file{configure.in}
+script.
+
+@node Invoking autoconf, Invoking autoheader, Writing configure.in, Making configure Scripts
+@section Invoking @code{autoconf}
+
+To create @code{configure} from @file{configure.in}, run the
+@code{autoconf} program with no arguments. @code{autoconf} processes
+@file{configure.in} with the @code{m4} macro processor, using the
+Autoconf macros. If you give @code{autoconf} an argument, it reads that
+file instead of @file{configure.in} and writes the configuration script
+to the standard output instead of to @file{configure}. If you give
+@code{autoconf} the argument @samp{-}, it reads the standard input
+instead of @file{configure.in} and writes the configuration script on
+the standard output.
+
+The Autoconf macros are defined in two or more files. Two of the files
+are distributed with Autoconf: @file{acgeneral.m4} (@pxref{General
+Purpose Macros}) and @file{acspecific.m4} (@pxref{Specific Tests}).
+@code{autoconf} also looks for an optional file called @file{aclocal.m4}
+both in the directory that contains other installed Autoconf macro files and
+in the current directory. (If both files exist, it uses both of them.)
+Those files can contain your site's own locally written Autoconf macro
+definitions. @xref{Writing Macros}, for more information.
+
+You can override the directory where @code{autoconf} looks for the
+installed macro files by setting the @code{AC_MACRODIR} environment
+variable to a different directory. You can also give @code{autoconf}
+the @samp{--macrodir} option, which overrides @code{AC_MACRODIR}.
+
+@code{autoconf} also accepts the options @code{--version}, which prints
+the Autoconf version number and exits, and @code{--help}, which prints a
+summary of the command-line options and exits.
+
+@node Invoking autoheader, , Invoking autoconf, Making configure Scripts
+@section Invoking @code{autoheader}
+
+You can use the program @code{autoheader} to create a template file of C
+@samp{#define} statements for @code{configure} to use. By default, the
+file that @code{autoheader} creates is called @file{config.h.in}; if
+@file{configure.in} invokes @code{AC_CONFIG_HEADER(@var{file})},
+@code{autoheader} creates @file{@var{file}.in}.
+
+@code{autoheader} scans @file{configure.in} and figures out which C
+preprocessor symbols it might define. It copies comments and
+@code{#define} and @code{#undef} statements from a file called
+@file{acconfig.h}, which comes with and is installed with Autoconf; it
+also uses a file called @file{acconfig.h} in the current directory, if
+present. For symbols that @code{AC_HAVE_HEADERS} or
+@code{AC_HAVE_FUNCS} define, @code{autoheader} generates comments and
+@code{#undef} statements itself rather than copying them from a file,
+since the possible symbols are effectively limitless.
+
+The file that @code{autoheader} creates contains only @code{#define} and
+@code{#undef} statements and their accompanying comments; there is no
+provision in @code{autoheader} for adding other code or comments to the
+file.
+
+If you give @code{autoheader} an argument, it uses that file instead of
+@file{configure.in} and writes the header file to the standard output
+instead of to @file{config.h.in}. If you give @code{autoheader} an
+argument of @samp{-}, it reads the standard input instead of
+@file{configure.in} and writes the header file to the standard output.
+
+You can override the directory where @code{autoheader} looks for the
+installed macro and @file{acconfig.h} files by setting the
+@code{AC_MACRODIR} environment variable to a different directory. You
+can also give @code{autoheader} the @samp{--macrodir} option, which
+overrides @code{AC_MACRODIR}.
+
+@code{autoheader} also accepts the options @code{--version}, which prints
+the Autoconf version number and exits, and @code{--help}, which prints a
+summary of the command-line options and exits.
+
+@node Specific Tests, General Purpose Macros, Making configure Scripts, Top
+@chapter Specific Tests
+
+These macros test for particular operating system features that packages
+might need or want to use. If you need to test for a feature that none
+of these macros check for, you can probably do it by calling one of the
+general purpose test macros with appropriate arguments (@pxref{General
+Tests}).
+
+All of these macros that set @code{make} variables call @code{AC_SUBST}
+on those variables (@pxref{Setting Variables}, for details about
+@code{AC_SUBST}). The phrase ``define @var{name}'' is used below as a
+shorthand to mean either add @samp{-D@var{name}=1} to the @code{make}
+variable @code{DEFS}, or put @samp{#define @var{name} 1} in the
+configuration header file, depending on whether @code{AC_CONFIG_HEADER} has
+been called. @xref{Setting Variables}, for more information.
+
+Within each section below, the macros are listed in alphabetical order.
+The macros are generally named for the @code{make} variables or C
+preprocessor macros that they define; those names are based largely on
+what existing GNU programs use. These macros are defined in the file
+@file{acspecific.m4}.
+
+@menu
+* Alternative Programs:: Selecting between alternative programs.
+* Header Files:: Header files that might be missing.
+* Typedefs:: @code{typedef}s that might be missing.
+* Library Functions:: C library functions that might be missing.
+* Structures:: Structures or members that might be missing.
+* Compiler Characteristics:: C compiler or machine architecture features.
+* System Services:: Operating system services.
+* UNIX Variants:: Special cases for specific UNIX variants.
+@end menu
+
+@node Alternative Programs, Header Files, , Specific Tests
+@section Alternative Programs
+
+The following macros check for the presence or behavior of particular
+programs:
+
+@defmac AC_DECLARE_YYTEXT
+@findex DECLARE_YYTEXT
+@vindex DECLARE_YYTEXT
+Define @code{DECLARE_YYTEXT} to declare @code{yytext} appropriately,
+depending on whether @code{lex} or @code{flex} is being used. This
+macro calls @code{AC_PROG_CPP} and @code{AC_PROG_LEX} if they haven't
+been called already.
+@end defmac
+
+@defmac AC_LN_S
+@findex LN_S
+If @samp{ln -s} works on the current filesystem (the O.S. and filesystem
+support symbolic links), set shell and @code{make} variable @code{LN_S}
+to @samp{ln -s}, otherwise set it to @samp{ln}.
+@end defmac
+
+@defmac AC_MINUS_C_MINUS_O
+@findex MINUS_C_MINUS_O
+@vindex NO_MINUS_C_MINUS_O
+If the C compiler does not accept the @samp{-c} and @samp{-o} options
+simultaneously, define @code{NO_MINUS_C_MINUS_O}.
+@end defmac
+
+@defmac AC_PROG_YACC
+@findex PROG_YACC
+If @code{bison} is found, set @code{make} variable @code{YACC} to
+@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
+to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@end defmac
+
+@defmac AC_PROG_CPP
+@findex PROG_CPP
+Set shell and @code{make} variable @code{CPP} to a command that runs the
+C preprocessor. If @samp{$CC -E} doesn't work, it uses @file{/lib/cpp}.
+
+Many of the specific test macros use the value of @code{CPP} indirectly
+by calling @code{AC_TEST_CPP}, @code{AC_HEADER_CHECK},
+@code{AC_HEADER_EGREP}, or @code{AC_PROGRAM_EGREP}. Those macros call
+this macro first if it hasn't been called already. It should be called
+after @code{AC_PROG_CC}.
+@end defmac
+
+@defmac AC_PROG_LEX
+@findex PROG_LEX
+If @code{flex} is found, set @code{make} variable @code{LEX} to
+@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
+standard place. Otherwise set @code{LEX} to @samp{lex} and
+@code{LEXLIB} to @samp{-ll}.
+@end defmac
+
+@defmac AC_PROG_AWK
+@findex PROG_AWK
+Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
+order, and set @code{make} variable @code{AWK} to the first one that it
+finds.
+@end defmac
+
+@defmac AC_PROG_CC
+@findex PROG_CC
+If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
+and set shell variable @code{GCC} to 1 for use by macros such as
+@code{AC_GCC_TRADITIONAL}.
+@end defmac
+
+@defmac AC_GCC_TRADITIONAL
+@findex GCC_TRADITIONAL
+Add @samp{-traditional} to @code{make} variable @code{CC} if using the
+GNU C compiler and @code{ioctl} does not work properly without
+@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
+@code{AC_PROG_CPP} if they haven't been called already.
+@end defmac
+
+@defmac AC_PROG_INSTALL
+@findex PROG_INSTALL
+Set @code{make} variable @code{INSTALL} to @samp{install -c} if
+@code{install} is found, otherwise set it to @samp{cp}. Screens out the
+false matches @file{/etc/install}, @file{/usr/sbin/install}, and other
+instances of @code{install} known not to work. The variable
+@code{INSTALL_PROGRAM} is set to @samp{$(INSTALL)} and
+@code{INSTALL_DATA} is set to @samp{$(INSTALL) -m 644}.
+@end defmac
+
+@defmac AC_PROG_RANLIB
+@findex PROG_RANLIB
+Set @code{make} variable @code{RANLIB} to @samp{ranlib} if @code{ranlib}
+is found, otherwise to @samp{:} (do nothing).
+@end defmac
+
+@defmac AC_RSH
+@findex RSH
+@vindex NO_REMOTE
+@vindex HAVE_NETDB_H
+If a remote shell is available, put @samp{rtapelib.o} in @code{make}
+variable @code{RTAPELIB}. Otherwise, also do so if @file{netdb.h}
+exists (implying the @code{rexec} function), and in addition define
+@code{HAVE_NETDB_H}. If neither a remote shell nor @code{rexec} is
+available, define @code{NO_REMOTE}.
+@end defmac
+
+@node Header Files, Typedefs, Alternative Programs, Specific Tests
+@section Header Files
+
+The following macros check for the presence of certain C header files:
+
+@defmac AC_DIR_HEADER
+@findex DIR_HEADER
+@vindex DIRENT
+@vindex SYSDIR
+@vindex SYSNDIR
+@vindex NDIR
+@vindex VOID_CLOSEDIR
+If the system has @file{dirent.h}, define @code{DIRENT}; otherwise, if
+it has @file{sys/ndir.h}, define @code{SYSNDIR}; otherwise, if it has
+@file{sys/dir.h}, define @code{SYSDIR}; otherwise, if it has
+@file{ndir.h}, define @code{NDIR}. Also, if the directory library
+header file contains a declaration of the @code{closedir} function with
+a @code{void} return type, define @code{VOID_CLOSEDIR}. The directory
+library declarations in the source code should look something like the
+following:
+
+@example
+@group
+/* unistd.h defines _POSIX_VERSION on POSIX.1 systems. */
+#if defined(DIRENT) || defined(_POSIX_VERSION)
+#include <dirent.h>
+#define NLENGTH(dirent) (strlen((dirent)->d_name))
+#else /* not (DIRENT or _POSIX_VERSION) */
+#define dirent direct
+#define NLENGTH(dirent) ((dirent)->d_namlen)
+#ifdef SYSNDIR
+#include <sys/ndir.h>
+#endif /* SYSNDIR */
+#ifdef SYSDIR
+#include <sys/dir.h>
+#endif /* SYSDIR */
+#ifdef NDIR
+#include <ndir.h>
+#endif /* NDIR */
+#endif /* not (DIRENT or _POSIX_VERSION) */
+@end group
+@end example
+
+Using the above declarations, the program would declare variables to be
+type @code{struct dirent}, not @code{struct direct}, and would access
+the length of a directory entry name by passing a pointer to a
+@code{struct dirent} to the @code{NLENGTH} macro.
+@end defmac
+
+@defmac AC_MAJOR_HEADER
+@findex MAJOR_HEADER
+@vindex MAJOR_IN_MKDEV
+@vindex MAJOR_IN_SYSMACROS
+If @file{sys/types.h} does not define @code{major}, @code{minor}, and
+@code{makedev}, but @file{sys/mkdev.h} does, define
+@code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define
+@code{MAJOR_IN_SYSMACROS}.
+@end defmac
+
+@defmac AC_MEMORY_H
+@findex MEMORY_H
+@vindex NEED_MEMORY_H
+Define @code{NEED_MEMORY_H} if @code{memcpy}, @code{memcmp}, etc. are
+not declared in @file{string.h} and @file{memory.h} exists. This macro
+is obsolete; instead, use @code{AC_HAVE_HEADERS(memory.h)}. See the
+example for @code{AC_STDC_HEADERS}.
+@end defmac
+
+@defmac AC_STDC_HEADERS
+@findex STDC_HEADERS
+@vindex STDC_HEADERS
+Define @code{STDC_HEADERS} if the system has ANSI C header files.
+Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h},
+@file{string.h}, and @file{float.h}; if the system has
+those, it probably has the rest of the ANSI C header files. This macro
+also checks whether @file{string.h} declares @code{memchr} (and
+thus presumably the other @code{mem} functions) and whether the
+@file{ctype.h} macros work on characters with the high bit set,
+as ANSI C requires.
+
+Use @code{STDC_HEADERS} instead of @code{__STDC__} to determine whether
+the system has ANSI-compliant header files (and probably C library
+functions) because many systems that have GCC do not have ANSI C header
+files.
+
+To check whether to use the System V/ANSI C string functions and header
+file, you can put the following in @file{configure.in}:
+
+@example
+AC_STDC_HEADERS
+AC_HAVE_HEADERS(string.h memory.h)
+@end example
+
+@noindent
+Then, in the code, use a test like this:
+
+@example
+@group
+#if STDC_HEADERS || HAVE_STRING_H
+#include <string.h>
+/* An ANSI string.h and pre-ANSI memory.h might conflict. */
+#if !STDC_HEADERS && HAVE_MEMORY_H
+#include <memory.h>
+#endif /* not STDC_HEADERS and HAVE_MEMORY_H */
+#define index strchr
+#define rindex strrchr
+#define bcopy(s, d, n) memcpy ((d), (s), (n))
+#define bcmp(s1, s2, n) memcmp ((s1), (s2), (n))
+#define bzero(s, n) memset ((s), 0, (n))
+#else /* not STDC_HEADERS and not HAVE_STRING_H */
+#include <strings.h>
+/* memory.h and strings.h conflict on some systems. */
+#endif /* not STDC_HEADERS and not HAVE_STRING_H */
+@end group
+@end example
+
+@noindent
+This example asssumes that your code uses the BSD style functions. If
+you use the System V/ANSI C style functions, you will need to replace
+the macro definitions with ones that go in the other direction.
+@end defmac
+
+@defmac AC_UNISTD_H
+@findex UNISTD_H
+@vindex HAVE_UNISTD_H
+Define @code{HAVE_UNISTD_H} if the system has @file{unistd.h}. The way
+to check if the system supports POSIX.1 is:
+
+@example
+@group
+#if HAVE_UNISTD_H
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+#ifdef _POSIX_VERSION
+/* Code for POSIX.1 systems. */
+#endif
+@end group
+@end example
+
+@vindex _POSIX_VERSION
+@code{_POSIX_VERSION} is defined when @file{unistd.h} is included on
+POSIX.1 systems. If there is no @file{unistd.h}, it is definitely not a
+POSIX.1 system. However, some non-POSIX.1 systems do have @file{unistd.h}.
+@end defmac
+
+@defmac AC_USG
+@findex USG
+@vindex USG
+Define @code{USG} if the system does not have @file{strings.h},
+@code{rindex}, @code{bzero}, etc. This implies that it has
+@file{string.h}, @code{strrchr}, @code{memset}, etc.
+
+The symbol @code{USG} is obsolete. Instead of this macro, use
+@code{AC_HAVE_HEADERS(string.h)} and use @code{HAVE_STRING_H} in your
+code. See the example for @code{AC_STDC_HEADERS}.
+@end defmac
+
+@node Typedefs, Library Functions, Header Files, Specific Tests
+@section Typedefs
+
+The following macros check for predefined C types:
+
+@defmac AC_GETGROUPS_T
+@findex GETGROUPS_T
+@vindex GETGROUPS_T
+Define @code{GETGROUPS_T} to be whichever of @code{gid_t} or @code{int}
+is the base type of the array argument to @code{getgroups}.
+@end defmac
+
+@defmac AC_MODE_T
+@findex MODE_T
+@vindex mode_t
+If @code{mode_t} is not defined in @file{sys/types.h}, define
+@code{mode_t} to be @code{int}.
+@end defmac
+
+@defmac AC_OFF_T
+@findex OFF_T
+@vindex off_t
+If @code{off_t} is not defined in @file{sys/types.h}, define
+@code{off_t} to be @code{long}.
+@end defmac
+
+@defmac AC_PID_T
+@findex PID_T
+@vindex pid_t
+If @code{pid_t} is not defined in @file{sys/types.h}, define
+@code{pid_t} to be @code{int}.
+@end defmac
+
+@defmac AC_RETSIGTYPE
+@findex RETSIGTYPE
+@vindex RETSIGTYPE
+If @file{signal.h} declares @code{signal} as returning a pointer to a
+function returning @code{void}, define @code{RETSIGTYPE} to be
+@code{void}; otherwise, define it to be @code{int}.
+
+Define signal handlers as returning type @code{RETSIGTYPE}:
+
+@example
+@group
+RETSIGTYPE
+hup_handler ()
+@{
+@dots{}
+@}
+@end group
+@end example
+@end defmac
+
+@defmac AC_SIZE_T
+@findex SIZE_T
+@vindex size_t
+If @code{size_t} is not defined in @file{sys/types.h}, define
+@code{size_t} to be @code{unsigned}.
+@end defmac
+
+@defmac AC_UID_T
+@findex UID_T
+@vindex uid_t
+@vindex gid_t
+If @code{uid_t} is not defined in @file{sys/types.h}, define
+@code{uid_t} to be @code{int} and @code{gid_t} to be @code{int}.
+@end defmac
+
+@node Library Functions, Structures, Typedefs, Specific Tests
+@section Library Functions
+
+The following macros check for particular C library functions:
+
+@defmac AC_ALLOCA
+@findex ALLOCA
+@vindex HAVE_ALLOCA_H
+Check how to get @code{alloca}. Tries to get a builtin version by
+checking for @file{alloca.h} or the predefined C preprocessor macros
+@code{__GNUC__} and @code{_AIX}. If that fails, it looks for a function
+in the standard C library. If that fails, it sets the @code{make}
+variable @code{ALLOCA} to @samp{alloca.o}. This variable is separate
+from @code{LIBOBJS} so multiple programs can share the value of
+@code{ALLOCA} without needing to create an actual library.
+
+If this macro finds @file{alloca.h}, it defines @code{HAVE_ALLOCA_H}.
+
+This macro does not try to get @code{alloca} from the SVR3 @file{libPW}
+or the SVR4 @file{libucb} because those libraries contain some
+incompatible functions that cause trouble. Some versions do not even
+contain @code{alloca} or contain a buggy version. If you still want to
+use their @code{alloca}, use @code{ar} to extract @file{alloca.o} from
+them instead of compiling @file{alloca.c}.
+
+Source files that use @code{alloca} should start with a piece of code
+like the following, to declare it properly. Note that in some versions
+of AIX, the declaration of @code{alloca} must precede everything else
+except for comments and preprocessor directives. The @code{#pragma}
+directive is indented so that pre-ANSI C compilers will ignore it,
+rather than choke on it.
+
+@example
+@group
+/* AIX requires this to be the first thing in the file. */
+#ifdef __GNUC__
+#define alloca __builtin_alloca
+#else /* not __GNUC__ */
+#if HAVE_ALLOCA_H
+#include <alloca.h>
+#else /* not HAVE_ALLOCA_H */
+#ifdef _AIX
+ #pragma alloca
+#else /* not _AIX */
+char *alloca ();
+#endif /* not _AIX */
+#endif /* not HAVE_ALLOCA_H */
+#endif /* not __GNUC__ */
+@end group
+@end example
+@end defmac
+
+@defmac AC_GETLOADAVG
+@findex GETLOADAVG
+@vindex NLIST_STRUCT
+@vindex NLIST_NAME_UNION
+@vindex GETLODAVG_PRIVILEGED
+@vindex NEED_SETGID
+Check how to get the system load averages. If the system has the
+@code{getloadavg} function, this macro defines @code{HAVE_GETLOADAVG},
+and adds to @code{LIBS} any libraries needed to get that function.
+
+Otherwise, it adds @samp{getloadavg.o} to the @code{make} variable
+@code{LIBOBJS}, and possibly defines several other C preprocessor
+macros and @code{make} variables:
+
+@enumerate
+@item
+It defines @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if
+on those systems.
+
+@item
+If it finds @file{nlist.h}, it defines @code{NLIST_STRUCT}.
+
+@item
+If @samp{struct nlist} has an @samp{n_un} member, it defines
+@code{NLIST_NAME_UNION}.
+
+@item
+If compiling @file{getloadavg.c} defines @code{LDAV_PRIVILEGED},
+programs need to be installed specially on this system for
+@code{getloadavg} to work, and this macro defines
+@code{GETLOADAVG_PRIVILEGED}.
+
+@item
+This macro always defines @code{NEED_SETGID}, for @code{make}. The
+value is @samp{true} if special installation is required, @samp{false}
+if not. If @code{NEED_SETGID} is @samp{true}, it sets @code{KMEM_GROUP}
+to the name of the group that should own the installed program.
+@end enumerate
+@end defmac
+
+@defmac AC_SETVBUF_REVERSED
+@findex SETVBUF_REVERSED
+@vindex SETVBUF_REVERSED
+If @code{setvbuf} takes the buffering type as its second argument and
+the buffer pointer as the third, instead of the other way around, define
+@code{SETVBUF_REVERSED}. This is the case on System V before release 3.
+@end defmac
+
+@defmac AC_STRCOLL
+@findex STRCOLL
+@vindex HAVE_STRCOLL
+Check for a proper declaration of the @code{strcoll} function. This
+does a bit more than @samp{AC_HAVE_FUNCS(strcoll)}, because some systems
+have incorrect definitions of @code{strcoll}, which should not be used.
+@end defmac
+
+@defmac AC_UTIME_NULL
+@findex UTIME_NULL
+@vindex HAVE_UTIME_NULL
+If @samp{utime(@var{file}, NULL)} sets @var{file}'s timestamp to
+the present, define @code{HAVE_UTIME_NULL}.
+@end defmac
+
+@defmac AC_VFORK
+@findex VFORK
+@vindex HAVE_VFORK_H
+@vindex vfork
+If @file{vfork.h} is found, define @code{HAVE_VFORK_H}. If a working
+@code{vfork} is not found, define @code{vfork} to be @code{fork}. This
+macro checks for several known errors in implementations of @code{vfork}
+and considers the system to not have a working @code{vfork} if it
+detects any of them.
+@end defmac
+
+@defmac AC_VPRINTF
+@findex VPRINTF
+@vindex HAVE_VPRINTF
+@vindex HAVE_DOPRNT
+If @code{vprintf} is found, define @code{HAVE_VPRINTF}. Otherwise, if
+@code{_doprnt} is found, define @code{HAVE_DOPRNT}.
+@end defmac
+
+@defmac AC_WAIT3
+@findex WAIT3
+@vindex HAVE_WAIT3
+If @code{wait3} is found and fills in the contents of its third argument
+(a @samp{struct rusage *}), which HP-UX does not do, define
+@code{HAVE_WAIT3}.
+@end defmac
+
+@node Structures, Compiler Characteristics, Library Functions, Specific Tests
+@section Structures
+
+The following macros check for certain structures or structure members:
+
+@defmac AC_STAT_MACROS_BROKEN
+@findex STAT_MACROS_BROKEN
+@findex STAT_MACROS_BROKEN
+If the macros @code{S_ISDIR}, @code{S_ISREG} et al. defined
+@file{sys/stat.h} do not work properly (returning false positives),
+define @code{STAT_MACROS_BROKEN}. This is the case on Tektronix UTekV,
+Amdahl UTS and Motorola System V/88.
+@end defmac
+
+@defmac AC_ST_BLKSIZE
+@findex ST_BLKSIZE
+@vindex HAVE_ST_BLKSIZE
+If @code{struct stat} contains an @code{st_blksize} member, define
+@code{HAVE_ST_BLKSIZE}.
+@end defmac
+
+@defmac AC_ST_BLOCKS
+@findex ST_BLOCKS
+@vindex HAVE_ST_BLOCKS
+If @code{struct stat} contains an @code{st_blocks} member, define
+@code{HAVE_ST_BLOCKS}. Otherwise, add @samp{fileblocks.o} to the
+@code{make} variable @code{LIBOBJS}.
+@end defmac
+
+@defmac AC_ST_RDEV
+@findex ST_RDEV
+@vindex HAVE_ST_RDEV
+If @code{struct stat} contains an @code{st_rdev} member, define
+@code{HAVE_ST_RDEV}.
+@end defmac
+
+@defmac AC_TIME_WITH_SYS_TIME
+@findex TIME_WITH_SYS_TIME
+@vindex TIME_WITH_SYS_TIME
+If a program may include both @file{time.h} and @file{sys/time.h},
+define @code{TIME_WITH_SYS_TIME}. On some older systems,
+@file{sys/time.h} includes @file{time.h}, but @file{time.h} is not
+protected against multiple inclusion, so programs should not explicitly
+include both files. This macro is useful in programs that use, for
+example, @code{struct timeval} or @code{struct timezone} as well as
+@code{struct tm}. It is best used in conjunction with
+@code{HAVE_SYS_TIME_H}.
+
+@example
+#ifdef TIME_WITH_SYS_TIME
+#include <sys/time.h>
+#include <time.h>
+#else
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#else
+#include <time.h>
+#endif
+#endif
+@end example
+@end defmac
+
+@defmac AC_STRUCT_TM
+@findex STRUCT_TM
+@vindex TM_IN_SYS_TIME
+If @file{time.h} does not define @code{struct tm}, define
+@code{TM_IN_SYS_TIME}, which means that including @file{sys/time.h}
+defines @code{struct tm}.
+@end defmac
+
+@defmac AC_TIMEZONE
+@findex TIMEZONE
+@vindex HAVE_TM_ZONE
+@vindex HAVE_TZNAME
+Figure out how to get the current timezone. If @code{struct tm} has a
+@code{tm_zone} member, define @code{HAVE_TM_ZONE}. Otherwise, if the
+external array @code{tzname} is found, define @code{HAVE_TZNAME}. This
+macro calls @code{AC_STRUCT_TM} if it hasn't been called already.
+@end defmac
+
+@node Compiler Characteristics, System Services, Structures, Specific Tests
+@section Compiler Characteristics
+
+The following macros check for C compiler or machine architecture
+features:
+
+@defmac AC_ARG_ARRAY
+@findex ARG_ARRAY
+@vindex NO_ARG_ARRAY
+If the address of an argument to a C function can not be used like
+the start of an array, define @code{NO_ARG_ARRAY}. This ability allows
+a sequence of arguments with the same type to be accessed as if they
+were an array of values.
+@end defmac
+
+@defmac AC_CROSS_CHECK
+@findex CROSS_CHECK
+If the C compiler being used does not produce executables that can run
+on the system where @code{configure} is being run, set the shell
+variable @code{cross_compiling} to 1. This information can be used by
+@code{AC_TEST_PROGRAM} to determine whether to take a default action
+instead of trying to run a test program (@pxref{General Tests}).
+@end defmac
+
+@defmac AC_CHAR_UNSIGNED
+@findex CHAR_UNSIGNED
+@vindex __CHAR_UNSIGNED__
+If the C type @code{char} is unsigned, define @code{__CHAR_UNSIGNED__},
+unless the C compiler predefines it.
+@end defmac
+
+@defmac AC_CONST
+@findex CONST
+@vindex const
+If the C compiler does not fully support the keyword @code{const},
+define @code{const} to be empty. Some C compilers that do not define
+@code{__STDC__} do support @code{const}; some compilers that define
+@code{__STDC__} do not completely support @code{const}. Programs can
+simply use @code{const} as if every C compiler supported it; for those
+that don't, the @file{Makefile} or configuration header file will define
+it as empty. (If using a configuration header file, the program should
+include it before any other header files, to prevent inconsistencies in
+declarations.)
+@end defmac
+
+@defmac AC_INLINE
+@findex INLINE
+@vindex inline
+If the C compiler is a version of GCC that supports the keyword
+@code{__inline} but not @code{inline} (such as some NeXT versions),
+define @code{inline} to be @code{__inline}. This macro calls
+@code{AC_PROG_CC} if it hasn't been called already.
+@end defmac
+
+@defmac AC_INT_16_BITS
+@findex INT_16_BITS
+@vindex INT_16_BITS
+If the C type @code{int} is smaller than the type @code{long}, define
+@code{INT_16_BITS}.
+@end defmac
+
+@defmac AC_LONG_DOUBLE
+@findex HAVE_LONG_DOUBLE
+@vindex HAVE_LONG_DOUBLE
+If the C compiler supports the @code{long double} type, define
+@code{HAVE_LONG_DOUBLE}. Some C compilers that do not define
+@code{__STDC__} do support the @code{long double} type; some compilers
+that define @code{__STDC__} do not support @code{long double}.
+@end defmac
+
+@defmac AC_WORDS_BIGENDIAN
+@findex WORDS_BIGENDIAN
+@vindex WORDS_BIGENDIAN
+If words are stored with the most significant byte first (like Motorola
+and SPARC, but not Intel and VAX, CPUs), define @code{WORDS_BIGENDIAN}.
+@end defmac
+
+@node System Services, UNIX Variants, Compiler Characteristics, Specific Tests
+@section System Services
+
+The following macros check for operating system services:
+
+@defmac AC_FIND_X
+@findex FIND_X
+Try to locate the X Window System include files and libraries by running
+@code{xmkmf} on a trivial @file{Imakefile} and examining the
+@file{Makefile} that it produces. If successful, set the shell
+variables @code{x_includes} and @code{x_libraries} to their locations;
+otherwise (such as if @code{xmkmf} is not present), do nothing.
+@end defmac
+
+@defmac AC_HAVE_POUNDBANG (@var{action-if-supported} @r{[}, @var{action-if-unsupported}@r{]})
+@findex HAVE_POUNDBANG
+Print @samp{checking if `#!' works in shell scripts} to the standard
+output. Then check whether the system supports starting shell scripts
+with a line of the form @samp{#!/bin/csh} to select the shell to run
+them with. @var{action-if-supported} is a list of shell commands to run
+if @samp{#!} works; @var{action-if-not-supported} is a list of shell
+commands to run otherwise.
+@end defmac
+
+@defmac AC_LONG_FILE_NAMES
+@findex LONG_FILE_NAMES
+@vindex HAVE_LONG_FILE_NAMES
+If the system supports file names longer than 14 characters, define
+@code{HAVE_LONG_FILE_NAMES}.
+@end defmac
+
+@defmac AC_REMOTE_TAPE
+@findex REMOTE_TAPE
+@vindex HAVE_SYS_MTIO_H
+If BSD tape drive ioctls are available, define @code{HAVE_SYS_MTIO_H},
+and if sockets are available add @code{rmt} to @code{make} variable
+@code{PROGS}.
+@end defmac
+
+@defmac AC_RESTARTABLE_SYSCALLS
+@findex RESTARTABLE_SYSCALLS
+@vindex HAVE_RESTARTABLE_SYSCALLS
+If the system automatically restarts a system call that is interrupted
+by a signal, define @code{HAVE_RESTARTABLE_SYSCALLS}.
+@end defmac
+
+@node UNIX Variants, , System Services, Specific Tests
+@section UNIX Variants
+
+The following macros check for certain operating systems that need
+special treatment for some programs, due to exceptional oddities in
+their header files or libraries:
+
+@defmac AC_AIX
+@findex AIX
+@vindex _ALL_SOURCE
+If on AIX, define @code{_ALL_SOURCE}. Allows the use of some BSD
+functions. Should be called before any macros that run the C compiler.
+@end defmac
+
+@defmac AC_DYNIX_SEQ
+@findex DYNIX_SEQ
+If on DYNIX/ptx (Sequent UNIX), add @samp{-lseq} to @code{make}
+variable @code{LIBS}. Allows use of some BSD system calls and
+@code{getmntent}.
+@end defmac
+
+@defmac AC_IRIX_SUN
+@findex IRIX_SUN
+If on IRIX (Silicon Graphics UNIX), add @samp{-lsun} to @code{make}
+variable @code{LIBS}. Needed to get @code{getmntent}. At sites using
+Yellow Pages/NIS, it is also needed to get properly working
+@code{gethostby*}, @code{getpw*}, @code{getgr*}, @code{getnetby*}, and
+so on.
+@c (According to Garrett.Wollman@uvm.edu.)
+@end defmac
+
+@defmac AC_ISC_POSIX
+@findex ISC_POSIX
+@vindex _POSIX_SOURCE
+If on a POSIXized ISC UNIX, define @code{_POSIX_SOURCE} and add
+@samp{-posix} (for the GNU C compiler) or @samp{-Xp} (for other C
+compilers) to @code{make} variable @code{CC}. This allows the use of
+POSIX facilities. Must be called after @code{AC_PROG_CC} and before
+any other macros that run the C compiler.
+@end defmac
+
+@defmac AC_MINIX
+@findex MINIX
+@vindex _MINIX
+@vindex _POSIX_SOURCE
+@vindex _POSIX_1_SOURCE
+If on Minix, define @code{_MINIX} and @code{_POSIX_SOURCE} and define
+@code{_POSIX_1_SOURCE} to be 2. This allows the use of POSIX
+facilities. Should be called before any macros that run the C compiler.
+@end defmac
+
+@defmac AC_SCO_INTL
+@findex SCO_INTL
+If on SCO UNIX, add @samp{-lintl} to @code{make} variable @code{LIBS}.
+Used to get @code{strftime}. It must be called before checking for
+@code{strftime}.
+@end defmac
+
+@defmac AC_XENIX_DIR
+@findex XENIX_DIR
+@vindex VOID_CLOSEDIR
+If on Xenix, define @code{VOID_CLOSEDIR} and add @samp{-lx} to
+@code{make} variable @code{LIBS}. Also, if @file{sys/ndir.h} is not
+being used, add @samp{-ldir} to @code{LIBS}. Needed when using the
+directory reading functions. This macro must be called after
+@code{AC_DIR_HEADER}.
+@end defmac
+
+@node General Purpose Macros, Writing Macros, Specific Tests, Top
+@chapter General Purpose Macros
+
+These macros provide ways for other macros to control the kind of output
+that Autoconf produces or to check whether various kinds of features are
+available. They all take arguments. When calling these macros, there
+must not be any blank space between the macro name and the open
+parentheses.
+
+Arguments to these macros can be more than one line long if they are
+enclosed within the @code{m4} quote characters @samp{[} and @samp{]}.
+
+Within each section below, the macros are listed in alphabetical order.
+These macros are defined in the file @file{acgeneral.m4}.
+
+@menu
+* Setup:: Controlling Autoconf operation.
+* General Tests:: Check for kinds of features.
+* Setting Variables:: Setting shell and @code{make} variables.
+* Macro Ordering:: Enforcing ordering constraints.
+@end menu
+
+@node Setup, General Tests, , General Purpose Macros
+@section Controlling Autoconf Setup
+
+The following macros control the kind of output that Autoconf produces.
+
+@defmac AC_CONFIG_HEADER (@var{header-to-create})
+@findex CONFIG_HEADER
+@vindex HAVE_CONFIG_H
+Make @code{AC_OUTPUT} create a file @var{header-to-create} containing C
+preprocessor @code{#define} statements and replace @samp{@@DEFS@@} in
+generated files with @samp{-DHAVE_CONFIG_H} instead of the value of
+@code{DEFS}. @xref{Setup}, for more information on @code{AC_OUTPUT}.
+This macro should be called right after @code{AC_INIT}. The usual name
+for @var{header-to-create} is @file{config.h}.
+
+If @var{header-to-create} already exists and its contents are identical
+to what @code{AC_OUTPUT} would put in it, it is left alone. Doing this
+allows some changes in configuration without needlessly causing object
+files that depend on the header file to be recompiled.
+
+Your distribution should contain a file @file{@var{header-to-create}.in}
+that looks as you want the final header file to look, including
+comments, with default values in the @code{#define} statements. A
+default value can be to @code{#undef} the variable instead of to define
+it to a value, if your code tests for configuration options using
+@code{#ifdef} instead of @code{#if}.
+
+You can use the program @code{autoheader} to create
+@file{@var{header-to-create}.in} (@pxref{Invoking autoheader}).
+@end defmac
+
+@defmac AC_INIT (@var{unique-file-in-source-dir})
+@findex INIT
+Process the command-line arguments and find the source code directory.
+@var{unique-file-in-source-dir} is some file that is in the package's
+source directory; @code{configure} checks for this file's existence to
+make sure that the directory that it is told contains the source code in
+fact does (@pxref{Running configure Scripts}, for more information).
+@end defmac
+
+@defmac AC_PREPARE (@var{unique-file-in-source-dir})
+@findex PREPARE
+Find the source code directory and set up shell variables necessary for
+other Autoconf macros to work. @var{unique-file-in-source-dir} is some
+file that is in the package's source directory; @code{configure} checks
+for this file's existence to make sure that the directory that it is
+told contains the source code in fact does (@pxref{Running configure
+Scripts}, for more information). @code{AC_PREPARE} is the last thing
+done by @code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT}
+if you want to do argument parsing yourself; never use both.
+@end defmac
+
+@defmac AC_OUTPUT (@r{[}@var{file}@dots{}@r{]})
+@findex OUTPUT
+Create output files (typically one or more @file{Makefile}s) and
+@file{config.status}. If @code{AC_CONFIG_HEADER} has been called, also
+create the header file that was named as its argument. The argument is
+a whitespace-separated list of files to create; if it is omitted, no
+files are created. @code{AC_OUTPUT} creates each file @file{@var{file}}
+in the list by copying @file{@var{file}.in}, substituting the variable
+values that have been selected by calling @code{AC_SUBST}. It creates
+the directory that each file is in if it doesn't exist (but not the
+parents of that directory). A plausible value for the argument to
+@code{AC_OUTPUT} is @samp{Makefile src/Makefile man/Makefile
+X/Imakefile}.
+@end defmac
+
+@defmac AC_REVISION (@var{revision-info})
+@findex REVISION
+Copy revision stamp @var{revision-info} into the @file{configure}
+script, with any dollar signs or double-quotes removed. This macro lets
+you put a revision stamp from @file{configure.in} into @file{configure}
+without RCS or CVS changing it when you check in @file{configure}. That
+way, you can determine easily which revision of @file{configure.in} a
+particular @file{configure} corresponds to.
+
+It is a good idea to call this macro before @code{AC_INIT} so that the
+revision number is near the top of both @file{configure.in} and
+@file{configure}. To support doing that, the @code{AC_REVISION} output
+begins with @samp{#!/bin/sh}, like the normal start of a
+@file{configure} script does.
+
+For example, this line in @file{configure.in}:
+
+@example
+ifdef([AC_REVISION],AC_REVISION($Revision$),)dnl
+@end example
+
+@noindent
+produces this in @file{configure}:
+
+@example
+#!/bin/sh
+# From configure.in Revision: 1.30
+@end example
+@end defmac
+
+@node General Tests, Setting Variables, Setup, General Purpose Macros
+@section Checking for Kinds of Features
+
+These macros are templates that, when called with actual parameters,
+check for various kinds of features. Many of these macros handle two
+cases: what to do if the given condition is met, and what to do if the
+condition is not met. In some places you you might want to do something
+if a condition is true but do nothing if it's false, or vice versa. To
+omit the true case, pass an empty value for the @var{action-if-found}
+argument to the macro. To omit the false case, omit the
+@var{action-if-not-found} argument to the macro, including the comma
+before it.
+
+One shell programming construction that you should not use in the action
+arguments to these macros is @samp{@var{var}=$@{@var{var}:-@var{value}@}}.
+Old BSD shells, including the Ultrix @code{sh}, don't understand the
+colon, and complain and die. If you omit the colon, it works fine:
+@samp{@var{var}=$@{@var{var}-@var{value}@}}.
+
+@xref{Writing Macros}, for more information on how best to use these
+macros.
+
+@defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex COMPILE_CHECK
+Print @samp{checking for @var{echo-text}} to the standard output. Then
+create a test C program to see whether a function whose body consists of
+@var{function-body} can be compiled and linked; @var{includes} is any
+@code{#include} statements needed by the code in @var{function-body}.
+If the file compiles and links successfully, run shell commands
+@var{action-if-found}, otherwise run @var{action-if-not-found}.
+@end defmac
+
+@defmac AC_FUNC_CHECK (@var{function}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex FUNC_CHECK
+If @var{function} is available, run shell commands
+@var{action-if-found}, otherwise @var{action-if-not-found}. If the
+functions might be in libraries other than the default C library, first
+call @code{AC_HAVE_LIBRARY} for those libraries. If you just want to
+define a symbol if the function is available, consider using
+@code{AC_HAVE_FUNCS} instead.
+@end defmac
+
+@defmac AC_HAVE_FUNCS (@var{function}@dots{})
+@findex HAVE_FUNCS
+@vindex HAVE_@var{function}
+For each given @var{function} in the whitespace-separated argument list
+that is available, define @code{HAVE_@var{function}} (in all caps).
+@xref{Specific Tests}, for a precise definition of ``define'' as it
+is used here. If the functions might be in libraries other than the
+default C library, first call @code{AC_HAVE_LIBRARY} for those libraries.
+@end defmac
+
+@defmac AC_HAVE_HEADERS (@var{header-file}@dots{})
+@findex HAVE_HEADERS
+@vindex HAVE_@var{header}
+For each given @var{header-file} in the whitespace-separated argument
+list that exists, define @code{HAVE_@var{header-file}} (in all caps).
+@xref{Specific Tests}, for a precise definition of ``define'' as
+it is used here.
+@end defmac
+
+@defmac AC_HAVE_LIBRARY (@var{library} @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]]})
+@findex HAVE_LIBRARY
+Print @samp{checking for @var{library}} to the standard output. Then
+create a test C program to see whether that program can be linked with
+the specified library. @var{action-if-found} is a list of shell
+commands to run if the link succeeds (which means that the library is
+present); @var{action-if-not-found} is a list of shell commands to run
+if the link fails. If @var{action-if-found} and
+@var{action-if-not-found} are not specified, the default action is to
+add @samp{-lfoo} to @code{LIBS} and define @samp{HAVE_LIBfoo}
+for library @samp{foo}. @var{library} can be written as any of
+@samp{foo}, @samp{-lfoo}, or @samp{libfoo.a}. In all of those cases,
+the compiler is passed @samp{-lfoo}.
+@end defmac
+
+@defmac AC_HEADER_CHECK (@var{header-file}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex HEADER_CHECK
+If @var{header-file} exists, execute shell commands
+@var{action-if-found}, otherwise execute @var{action-if-not-found}. If
+you just want to define a symbol if the header file is available,
+consider using @code{AC_HAVE_HEADERS} instead.
+@end defmac
+
+@defmac AC_HEADER_EGREP (@var{pattern}, @var{header-file}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex HEADER_EGREP
+If the output of running the C preprocessor on @var{header-file}
+contains the @code{egrep} regular expression @var{pattern}, execute
+shell commands @var{action-if-found}, otherwise execute
+@var{action-if-not-found}.
+
+You can not check whether preprocessor symbols are defined this way,
+because they get expanded before @code{egrep} sees them. You can
+probably just put @code{#ifdef} directives in your C programs to detect
+them, but if you want to do the check in @code{configure} for some
+reason (perhaps to determine which of several files to include), then
+use @code{AC_PROGRAM_EGREP}, like this:
+
+@example
+AC_PROGRAM_EGREP(yes, [#include <stdio.h>
+#ifdef P_tmpdir
+yes
+#endif
+], AC_DEFINE(HAVE_P_TMPDIR))
+@end example
+@end defmac
+
+@defmac AC_PREFIX (@var{program})
+@findex PREFIX
+If the user did not specify an installation prefix on the command line,
+guess a value for it by looking for @var{program} in @code{PATH}, the
+way the shell does. If @var{program} is found, set the prefix to the
+parent of the directory containing @var{program}; otherwise leave the
+prefix specified in @file{Makefile.in} unchanged. For example, if
+@var{program} is @code{gcc} and the @code{PATH} contains
+@file{/usr/local/gnu/bin/gcc}, set the prefix to @file{/usr/local/gnu}.
+@end defmac
+
+@defmac AC_PROGRAM_CHECK (@var{variable}, @var{prog-to-check-for}, @var{value-if-found}, @var{value-if-not-found})
+@findex PROGRAM_CHECK
+Check whether program @var{prog-to-check-for} exists in @code{PATH}. If
+it is found, set @var{variable} to @var{value-if-found}, otherwise to
+@var{value-if-not-found}. Calls @code{AC_SUBST} for @var{variable}.
+@end defmac
+
+@defmac AC_PROGRAM_EGREP (@var{pattern}, @var{program}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex PROGRAM_EGREP
+@var{program} is the text of a C program, on which shell variable and
+backquote substitutions are performed. If the output of running the C
+preprocessor on @var{program} contains the @code{egrep} regular
+expression @var{pattern}, execute shell commands @var{action-if-found},
+otherwise execute @var{action-if-not-found}. (It is an unfortunate
+oversight that we use the word ``PROGRAM'' in Autoconf macro names to
+sometimes mean C source code and sometimes mean a UNIX command.)
+@end defmac
+
+@defmac AC_PROGRAMS_CHECK (@var{variable}, @var{progs-to-check-for} @r{[}, @var{value-if-not-found}@r{]})
+@findex PROGRAMS_CHECK
+Check for each program in the whitespace-separated list
+@var{progs-to-check-for} exists in @code{PATH}. If it is found, set
+@var{variable} to the name of that program. Otherwise, continue
+checking the next program in the list. If none of the programs in the
+list are found, set @var{variable} to @var{value-if-not-found}; if
+@var{value-if-not-found} is not specified, the value of @var{variable}
+will not be changed. Calls @code{AC_SUBST} for @var{variable}.
+@end defmac
+
+@defmac AC_REPLACE_FUNCS (@var{function-name}@dots{})
+@findex REPLACE_FUNCS
+For each given @var{function-name} in the whitespace-separated argument
+list that is not in the C library, add @samp{@var{function-name}.o} to
+the value of the @code{make} variable @code{LIBOBJS}. If the functions
+might be in libraries other than the default C library, first call
+@code{AC_HAVE_LIBRARY} for those libraries.
+@end defmac
+
+@defmac AC_TEST_PROGRAM (@var{program}, @var{action-if-true} @r{[}, @var{action-if-false} @r{[}, @var{action-if-cross-compiling}@r{]]})
+@findex TEST_PROGRAM
+@var{program} is the text of a C program, on which shell variable and
+backquote substitutions are performed. If it compiles and links
+successfully and returns an exit status of 0 when executed, run shell
+commands @var{action-if-true}. Otherwise run shell commands
+@var{action-if-false}.
+
+If the optional argument @var{action-if-cross-compiling} is given and
+the C compiler being used does not produce executables that run on the
+system where @code{configure} is being run, then the test program is not
+run. Instead, the shell commands @var{action-if-cross-compiling} are
+run. If that argument is given, this macro calls @code{AC_CROSS_CHECK}
+if it has not already been called (@pxref{Compiler Characteristics}).
+@end defmac
+
+@defmac AC_TEST_CPP (@var{includes}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]})
+@findex TEST_CPP
+@var{includes} is C @code{#include} statements and declarations, on
+which shell variable and backquote substitutions are performed.
+(Actually, it can be any C program, but other statements are probably
+not useful.) If the C preprocessor produces no error messages while
+processing it, run shell commands @var{action-if-true}. Otherwise run
+shell commands @var{action-if-false}.
+
+This macro calls @code{AC_PROG_CPP} if it hasn't been called already.
+@end defmac
+
+@defmac AC_WITH (@var{feature}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]})
+@findex WITH
+If the user gave @code{configure} the option
+@samp{--with-@var{feature}}, run shell commands @var{action-if-true}.
+Otherwise run shell commands @var{action-if-false}. The name
+@var{feature} should consist only of alphanumeric characters and dashes;
+typical feature names are @samp{gnu-libc} and @samp{x}.
+
+The user can give a value by following the feature name with @samp{=}
+and the value; for example,
+
+@example
+./configure --with-targets=sun4,hp300bsd
+@end example
+
+The value given is available to the shell commands @var{action-if-true}
+in the shell variable @code{withval}. If no value was given,
+@code{withval} is 1. For example,
+
+@example
+AC_WITH(fubar, echo "got --with-fubar=$withval",
+ echo no --with-fubar)
+@end example
+@end defmac
+
+@node Setting Variables, Macro Ordering, General Tests, General Purpose Macros
+@section Setting Variables
+
+These macros help other macros to define shell and @code{make}
+variables.
+
+@defmac AC_DEFINE (@var{variable} @r{[}, @var{value}@r{]})
+@findex DEFINE
+Define C preprocessor variable @var{variable}. If @var{value} is given,
+set @var{variable} to that value, otherwise set it to 1. To use a shell
+variable as the value, use @code{AC_DEFINE_UNQUOTED} instead. Precede
+double quotes in the value with backslashes.
+
+This macro adds to the shell variable @code{DEFS}. @code{AC_OUTPUT}
+later substitutes the values in @code{DEFS} into the file(s) that it
+generates (typically @file{Makefile}). Alternately, if
+@code{AC_CONFIG_HEADER} has been called, @code{AC_OUTPUT} creates a
+header file by substituting the correct values into @code{#define}
+statements in a template file.
+
+For example, suppose your @file{configure.in} calls
+@code{AC_CONFIG_HEADER(conf.h)} and @code{AC_UNISTD_H}. You could have
+code like this in @file{conf.h.in}:
+
+@example
+@group
+/* Define as 1 if you have unistd.h. */
+#define HAVE_UNISTD_H 0
+@end group
+@end example
+
+On systems that have @file{unistd.h}, @code{configure} will change the 0
+to a 1. On other systems, it will leave the line unchanged.
+Alternately, if you prefer to use @code{#ifdef}, your @file{conf.h.in}
+could have code like this:
+
+@example
+@group
+/* Define if you have unistd.h. */
+#undef HAVE_UNISTD_H
+@end group
+@end example
+
+On systems that have @file{unistd.h}, @code{configure} will change the
+second line to read @samp{#define HAVE_UNISTD_H 1}. On other systems,
+it will leave the line unchanged.
+
+Due to the syntactical bizarreness of the Bourne shell, do not use
+semicolons to separate @code{AC_DEFINE} calls from other macro calls or
+shell code; that can cause syntax errors in the resulting
+@code{configure} script. Use either spaces or newlines. That is, do
+this:
+
+@example
+AC_HEADER_CHECK(elf.h, AC_DEFINE(SVR4) LIBS="$LIBS -lelf")
+@end example
+
+@noindent
+or this:
+
+@example
+AC_HEADER_CHECK(elf.h,
+ AC_DEFINE(SVR4)
+ LIBS="$LIBS -lelf")
+@end example
+
+@noindent
+instead of this:
+
+@example
+AC_HEADER_CHECK(elf.h, AC_DEFINE(SVR4); LIBS="$LIBS -lelf")
+@end example
+@end defmac
+
+@defmac AC_DEFINE_UNQUOTED (@var{variable} @r{[}, @var{value}@r{]})
+@findex DEFINE_UNQUOTED
+Like @code{AC_DEFINE}, but it does nothing to quote @var{value} from
+various shell and @code{sed} expansions it will undergo. @var{value}
+will be used in many different contexts requiring different quoting, and
+it is up to you to make sure it works right. Use this macro instead of
+@code{AC_DEFINE} when @var{value} contains a shell variable. For
+example:
+
+@example
+AC_DEFINE_UNQUOTED(config_machfile, $@{machfile@})
+@end example
+@end defmac
+
+@defmac AC_SUBST (@var{variable})
+@findex SUBST
+Substitute the variable @var{variable} when creating the output files
+(typically one or more @file{Makefile}s). This means replace instances
+of @samp{@@@var{variable}@@}, e.g. in @file{Makefile.in}, with the
+current value of the shell variable @var{variable}. If this macro were
+not called, the value of @var{variable} would not be set in the output
+files, even though @code{configure} had figured out a value for it.
+
+You can set or add to the value of @var{variable} in the usual shell
+way. For example, to add @samp{-ltermcap} to the value of the variable
+@code{LIBS}:
+
+@example
+LIBS="$LIBS -ltermcap"
+@end example
+@end defmac
+
+@node Macro Ordering, , Setting Variables, General Purpose Macros
+@section Macro Ordering
+
+These macros provide ways for other macros to make sure that they are
+called in the correct order.
+
+@defmac AC_BEFORE (@var{this-macro-name}, @var{called-macro-name})
+@findex BEFORE
+Make @code{m4} print a warning message on the standard error output if
+@var{called-macro-name} has already been called. @var{this-macro-name}
+should be the name of the macro that is calling @code{AC_BEFORE}. The
+macro @var{called-macro-name} must contain a call to @code{AC_PROVIDE}
+to indicate that it has been called.
+
+This macro should be used when one macro makes changes that might affect
+another macro, so that the other macro should probably not be called
+first. For example, @code{AC_PROG_CPP} checks whether the C compiler
+can run the C preprocessor when given the @samp{-E} option. It should
+therefore be called after any macros that change which C compiler is
+being used, such as @code{AC_PROG_CC}. So @code{AC_PROG_CC} contains:
+
+@example
+AC_BEFORE([$0], [AC_PROG_CPP])
+@end example
+
+@noindent
+This warns the user if a call to @code{AC_PROG_CPP} has already occurred
+when @code{AC_PROG_CC} is called.
+@end defmac
+
+@defmac AC_PROVIDE (@var{macro-name})
+@findex PROVIDE
+Set a flag recording that @var{macro-name} has been called. The
+argument should be the name of the macro that is calling
+@code{AC_PROVIDE}. An easy way to get it is from the @code{m4} builtin
+variable @code{$0}, like this:
+
+@example
+AC_PROVIDE([$0])
+@end example
+@end defmac
+
+@defmac AC_REQUIRE (@var{macro-name})
+@findex REQUIRE
+If the @code{m4} macro @var{macro-name} has not already been called,
+call it (without any arguments). Make sure to quote @var{macro-name}
+with square brackets. The body of @var{macro-name} must contain a call
+to @code{AC_PROVIDE} to indicate that it has been called.
+
+Macros that need some other macro to be called before they are called
+can use @code{AC_REQUIRE} to ensure that it has been, in case the person
+who made @file{configure.in} forgot or didn't know to do it.
+@code{AC_REQUIRE} and @code{AC_PROVIDE} together can ensure that a macro
+is only called if it is needed, and only called once.
+@xref{Dependencies Between Macros}, for more information.
+@end defmac
+
+@node Writing Macros, Makefiles, General Purpose Macros, Top
+@chapter Writing Macros
+
+If your package needs to test for some feature that none of the macros
+supplied with Autoconf handles, you'll need to write one or more new
+Autoconf macros. Here are some suggestions and some of the rationale
+behind why the existing macros are written the way they are. You can
+also learn a lot about how to write Autoconf macros by looking at the
+existing ones. If something goes wrong in one or more of the Autoconf
+tests, this information can help you understand why they work the way
+they do and the assumptions behind them, which might help you figure out
+how to best solve the problem.
+
+If you add macros that you think would be useful to other people, or
+find problems with the distributed macros, please send electronic mail
+to @file{bug-gnu-utils@@prep.ai.mit.edu}, so we can consider them for
+future releases of Autoconf. Please include the Autoconf version
+number, which you can get by running @samp{autoconf --version}.
+
+@menu
+* Macro Format:: Basic format of an Autoconf macro.
+* Quoting:: Protecting macros from unwanted expansion.
+* Dependencies Between Macros:: What to do when macros depend on other macros.
+* Checking for Files:: Finding whether a file exists.
+* Checking for Symbols:: Finding whether a symbol is defined.
+* Test Programs:: Writing programs to test for features.
+* Multiple Cases:: Tests for several possible values.
+@end menu
+
+@node Macro Format, Quoting, , Writing Macros
+@section Macro Format
+
+Autoconf macros are defined as arguments to the @code{m4} builtin
+command @code{define}. Their overall structure looks like this:
+
+@example
+define(@var{macro-name}, [@var{macro-body}])dnl
+@end example
+
+@noindent
+The square brackets here do not indicate optional text: they should
+literally be present in the macro definition.
+
+All of the Autoconf macros have names starting with @samp{AC_} to
+prevent them from accidentally conflicting with other text. You should
+prefix your own macro names with some other sequence, such as your
+initials or an abbreviation for the name of your organization or
+software package, to ensure that their names don't conflict with the
+names of present or future Autoconf macros.
+
+The @code{m4} builtin @code{dnl} prevents a newline from being inserted
+in the output where the macro is defined; without it, the generated
+@code{configure} script would begin with dozens of blank lines.
+@code{dnl} is also used to introduce comments in @code{m4}; it causes
+@code{m4} to discard the rest of the input line.
+
+You should quote the entire macro body with square brackets to avoid
+macro expansion problems (@pxref{Quoting}). You can refer to any
+arguments passed to the macro as @samp{$1}, @samp{$2}, etc.
+
+@xref{Definitions, , How to define new macros, m4.info, GNU m4}, for
+more complete information on writing @code{m4} macros.
+
+@node Quoting, Dependencies Between Macros, Macro Format, Writing Macros
+@section Quoting
+
+Macros that are called by other macros are evaluated by @code{m4}
+several times; each evaluation might require another layer of quotes to
+prevent unwanted expansions of macros or @code{m4} builtins, such as
+@samp{include} and @samp{$1}. Quotes are also required around macro
+arguments that contain commas, since commas separate the arguments from
+each other.
+
+Autoconf (in @file{acgeneral.m4}) changes the @code{m4} quote characters
+from the default @samp{`} and @samp{'} to @samp{[} and @samp{]}, because
+many of the macros use @samp{`} and @samp{'}, mismatched. However, in a
+few places the macros need to use brackets. In those places, they use
+the @code{m4} builtin command @code{changequote} to temporarily disable
+quoting before the code that uses brackets, like this:
+
+@example
+changequote(,)dnl
+@end example
+
+@noindent
+Then they turn quoting back on again with another call to
+@code{changequote}:
+
+@example
+changequote([,])dnl
+@end example
+
+When you create a @code{configure} script using newly written macros,
+examine it carefully to check whether you need to add more quotes in
+your macros. If one or more words have disappeared in the @code{m4}
+output, you need more quotes. When in doubt, quote.
+
+However, it's also possible to put on too many layers of quotes. If
+this happens, the resulting @code{configure} script will contain
+unexpanded macros. The @code{autoconf} program checks for this problem
+by doing @samp{grep AC_ configure}.
+
+@node Dependencies Between Macros, Checking for Files, Quoting, Writing Macros
+@section Dependencies Between Macros
+
+Some Autoconf macros depend on other macros having been called first in
+order to work correctly. Autoconf provides a way to ensure that certain
+macros are called if needed and a way to warn the user if macros are
+called in an order that might cause incorrect operation.
+
+@menu
+* Prerequisite Macros:: Ensuring required information.
+* Suggested Ordering:: Warning about possible ordering problems.
+@end menu
+
+@node Prerequisite Macros, Suggested Ordering, , Dependencies Between Macros
+@subsection Prerequisite Macros
+
+A macro that you write might need to use values that have previously
+been computed by other macros. For example, if you write a new macro
+that uses the C preprocessor, it depends on @code{AC_PROG_CPP} having
+been called first to set the shell variable @code{CPP}
+(@pxref{Alternative Programs}).
+
+Rather than forcing the user of the macros to keep track of all of the
+dependencies between them, you can use the macros @code{AC_PROVIDE} and
+@code{AC_REQUIRE} to do it automatically. @xref{Macro Ordering}, for more
+information on their syntax.
+
+The new macro that runs the C preprocessor should contain, somewhere
+before @code{CPP} is used, the statement
+
+@example
+AC_REQUIRE([AC_PROG_CPP])
+@end example
+
+@noindent
+and the macro @code{AC_PROG_CPP} should contain the statement (anywhere
+in its body)
+
+@example
+AC_PROVIDE([$0])
+@end example
+
+@noindent
+Then, when the new macro is run, it will invoke @code{AC_PROG_CPP} if
+and only if @code{AC_PROG_CPP} has not already been run.
+
+@node Suggested Ordering, , Prerequisite Macros, Dependencies Between Macros
+@subsection Suggested Ordering
+
+Some macros should be run before another macro if both are called, but
+neither requires the other to be called. For example, a macro like
+@code{AC_AIX} that changes the behavior of the C compiler (@pxref{UNIX
+Variants}) should be called before any macros that run the C compiler.
+Many of these dependencies are noted in the documentation.
+
+Autoconf provides a way to warn users when macros with this kind of
+dependency appear out of order in a @file{configure.in} file. The
+warning occurs when creating @file{configure} from @file{configure.in},
+not when running @file{configure}. It is not a fatal error;
+@file{configure} is created as usual.
+
+The @code{AC_BEFORE} macro causes @code{m4} to print a warning message
+on the standard error output when a macro is used before another macro
+which might change its behavior. The macro which should come first
+should contain a call to @code{AC_BEFORE} and the macro which should
+come later should contain a call to @code{AC_PROVIDE}.
+
+For example, @code{AC_AIX} contains
+
+@example
+AC_BEFORE([$0], [AC_COMPILE_CHECK])
+@end example
+
+@noindent
+and @code{AC_COMPILE_CHECK} contains
+
+@example
+AC_PROVIDE([$0])
+@end example
+
+@noindent
+As a result, if @code{AC_AIX} is called after @code{AC_COMPILE_CHECK},
+it will note that @code{AC_COMPILE_CHECK} has already been called and
+print a warning message.
+
+@node Checking for Files, Checking for Symbols, Dependencies Between Macros, Writing Macros
+@section Checking for Files
+
+If you need to check whether a file other than a C header file exists,
+use @samp{test -f @var{filename}}. If you need to make multiple checks
+using @code{test}, combine them with the shell operators @samp{&&} and
+@samp{||} instead of using the @code{test} operators @samp{-a} and
+@samp{-o}. On System V, the precedence of @samp{-a} and @samp{-o} is
+wrong relative to the unary operators; consequently, POSIX does not
+specify them, so using them is nonportable. If you combine @samp{&&}
+and @samp{||} in the same statement, keep in mind that they have equal
+precedence.
+
+Do not use @samp{test -x}, because 4.3BSD does not have it. Use
+@samp{test -f} or @samp{test -r} instead.
+
+@node Checking for Symbols, Test Programs, Checking for Files, Writing Macros
+@section Checking for Symbols
+
+If you need to check whether a symbol is defined in a C header file, you
+can use @code{AC_HEADER_EGREP} if the symbol is not a C preprocessor
+macro (@pxref{General Tests}), or compile a small test program that includes
+the file and references the symbol (@pxref{Test Programs}). Don't
+directly @code{grep} for the symbol in the file, because on some systems
+it might be defined in another header file that the file you are
+checking @samp{#include}s.
+
+However, if you need to check for a particular UNIX variant which is
+distinguished by having certain text in a certain file, then use
+@code{grep} (or @code{egrep}). But don't use @samp{grep -s} to suppress
+output, because @samp{grep -s} on System V does not suppress output,
+only error messages. Instead, redirect the standard output and standard
+error (in case the file doesn't exist) of @code{grep} to
+@file{/dev/null}. Check the exit status of @code{grep} to determine
+whether it found a match.
+
+To check whether the Autoconf macros have already defined a certain C
+preprocessor symbol, you can use a @code{case} statement like this:
+
+@example
+case "$DEFS" in
+ *HAVE_FOO*) ;;
+ *) LIBOBJS="$LIBOBJS foo.o" ;;
+esac
+@end example
+
+@noindent
+Make sure to enclose the variable name you are checking (usually
+@code{DEFS}) in double quotes, because otherwise some old versions of
+@code{bash} misinterpret the statement.
+
+@node Test Programs, Multiple Cases, Checking for Symbols, Writing Macros
+@section Test Programs
+
+Autoconf checks for many features by compiling small test programs. To
+find out whether a library function is available, Autoconf tries to
+compile a small program that uses it. This is unlike Larry Wall's
+Metaconfig, which uses @code{nm} or @code{ar} on the C library to try to
+figure out which functions are available. Trying to link with the
+function is usually a more reliable and flexible approach because it
+avoids dealing with the variations in the options and output formats of
+@code{nm} and @code{ar} and in the location of the standard libraries.
+It also allows @code{configure} to check aspects of the function's
+runtime behavior if needed. On the other hand, it is sometimes slower
+than scanning the libraries.
+
+If you need to check for a condition other than whether some symbol
+exists on the system or has a certain value, then you can't use
+@code{AC_COMPILE_CHECK} (@pxref{General Tests}). You have to write a
+test program by hand. You can compile and run it using
+@code{AC_TEST_PROGRAM} (@pxref{General Tests}).
+
+Try to avoid writing test programs if possible, because using them
+prevents people from configuring your package for cross-compiling. If
+it's really best that you test for a run-time behavior, try to provide a
+default ``worst case'' value to use when cross-compiling makes run-time
+tests impossible. You do this by passing the optional last argument to
+@code{AC_TEST_PROGRAM}.
+
+@menu
+* Guidelines:: General rules for writing test programs.
+* Tricks:: Special ways to work around problems.
+@end menu
+
+@node Guidelines, Tricks, , Test Programs
+@subsection Guidelines for Test Programs
+
+Test programs should return 0 if the test succeeds, nonzero otherwise,
+so that success can be distinguished easily from a core dump or other
+failure; segmentation violations and other failures produce a nonzero
+exit status. Test programs should @code{exit}, not @code{return}, from
+@code{main}, because on some systems the argument to @code{return} in
+@code{main} is ignored. They should not write anything to the standard
+output.
+
+Test programs can use @code{#if} or @code{#ifdef} to check the values of
+preprocessor macros defined by tests that have already run. For
+example, if you call @code{AC_STDC_HEADERS}, then later on in
+@file{configure.in} you can have a test program that includes an ANSI C
+header file conditionally:
+
+@example
+@group
+#if STDC_HEADERS
+#include <stdlib.h>
+#endif
+@end group
+@end example
+
+If a test program needs to use or create a data file, give it a name
+that starts with @file{conftest}, such as @file{conftestdata}. The
+@code{configure} script cleans up by running @samp{rm -rf conftest*}
+after running test programs and if the script is interrupted.
+
+@node Tricks, , Guidelines, Test Programs
+@subsection Tricks for Test Programs
+
+If a test program calls a function with invalid parameters (just to see
+whether it exists), organize the program to ensure that it never invokes
+that function. You can do this by calling it in another function that is
+never invoked. You can't do it by putting it after a call to
+@code{exit}, because GCC version 2 knows that @code{exit} never returns
+and optimizes out any code that follows it in the same block.
+
+If you include any header files, make sure to call the functions
+relevant to them with the correct number of arguments, even if they are
+just 0, to avoid compilation errors due to prototypes. GCC version 2
+has internal prototypes for several functions that it automatically
+inlines; for example, @code{memcpy}. To avoid errors when checking for
+them, either pass them the correct number of arguments or redeclare them
+with a different return type (such as @code{char}).
+
+@node Multiple Cases, , Test Programs, Writing Macros
+@section Multiple Cases
+
+Some operations are accomplished in several possible ways, depending on
+the UNIX variant. Checking for them essentially requires a ``case
+statement''. Autoconf does not directly provide one; however, it is
+easy to simulate by using a shell variable to keep track of whether a
+way to perform the operation has been found yet.
+
+Here is an example excerpted from the @file{configure.in} for GNU
+@code{find}. It uses the shell variable @code{fstype} to keep track of
+whether the remaining cases need to be checked. There are several more
+cases which are not shown here but follow the same pattern.
+
+@example
+@group
+echo checking how to get filesystem type
+# SVR4.
+AC_TEST_CPP([#include <sys/statvfs.h>
+#include <sys/fstyp.h>], AC_DEFINE(FSTYPE_STATVFS) fstype=1)
+if test -z "$fstype"; then
+# SVR3.
+AC_TEST_CPP([#include <sys/statfs.h>
+#include <sys/fstyp.h>], AC_DEFINE(FSTYPE_USG_STATFS) fstype=1)
+fi
+if test -z "$fstype"; then
+# AIX.
+AC_TEST_CPP([#include <sys/statfs.h>
+#include <sys/vmount.h>], AC_DEFINE(FSTYPE_AIX_STATFS) fstype=1)
+fi
+@end group
+@end example
+
+@node Makefiles, Running configure Scripts, Writing Macros, Top
+@chapter Makefiles
+
+Each subdirectory in a distribution should come with a file
+@file{Makefile.in}, from which @code{configure} will produce a
+@file{Makefile} in that directory. Most of the substitutions that
+@code{configure} does are simple: for each configuration variable that
+the package uses, it just replaces occurrences of
+@samp{@@@var{variable}@@} with the value that @code{configure} has
+determined for that variable. Any occurrences of
+@samp{@@@var{variable}@@} for variables that @code{configure} does not
+know about are passed through unchanged.
+
+There is no point in checking for the correct value to give a variable
+that is never used. Every variable that the @code{configure} script
+might set a value for should appear in a @samp{@@@var{variable}@@} reference
+in at least one @file{Makefile.in}. If @code{AC_CONFIG_HEADER} is
+called, @code{configure} replaces @samp{@@DEFS@@} with
+@samp{-DHAVE_CONFIG_H}, since the contents of @code{DEFS} would be
+redundant.
+
+@xref{Makefiles, , Makefile Conventions, standards.info, The GNU Coding
+Standards}, for more information on what to put in Makefiles.
+@xref{Sample Makefile.in}, for an example of a real @file{Makefile.in}.
+
+@menu
+* Predefined Variables:: Heavily used @code{make} variables.
+* Installation Prefixes:: A special variable substitution.
+* VPATH Substitutions:: Compiling in a different directory.
+* Automatic Remaking:: Makefile rules for configuring.
+@end menu
+
+@node Predefined Variables, Installation Prefixes, , Makefiles
+@section Predefined Variables
+
+Some @code{make} variables are predefined by the Autoconf macros.
+@code{AC_SUBST} is called for them automatically (@pxref{Setting
+Variables}), so in your @file{Makefile.in} files you can get their
+values by enclosing their names in @samp{@@} characters
+(@pxref{Makefiles}). The variables that are defined by the general
+purpose Autoconf macros are:
+
+@defvar srcdir
+The directory that contains the source code for that @file{Makefile}.
+@end defvar
+
+@defvar DEFS
+@samp{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADER}
+is called, @code{configure} replaces @samp{@@DEFS@@} with
+@samp{-DHAVE_CONFIG_H}, since the contents of @code{DEFS} would be
+redundant.
+@end defvar
+
+@defvar LIBS
+@samp{-l} and @samp{-L} options to pass to the linker.
+@end defvar
+
+@defvar LIBOBJS
+Names of object files (ending in @file{.o}). Set by
+@code{AC_REPLACE_FUNCS} (@pxref{General Tests}).
+@end defvar
+
+@node Installation Prefixes, VPATH Substitutions, Predefined Variables, Makefiles
+@section Installation Prefixes
+
+If @code{configure} has figured out a value for the installation prefix,
+either by the user supplying one on the command line (@pxref{Running
+configure Scripts}) or with @code{AC_PREFIX}, then it substitutes that
+value in @file{Makefile}s that it creates. Wherever a @file{Makefile.in}
+contains a line like
+
+@example
+prefix = /usr/local
+@end example
+
+@noindent
+@code{configure} substitutes the value it figured out. The word
+@samp{prefix} must not be preceded by any other characters on the line.
+If @code{configure} has not figured out a value for the prefix, the
+value in the @file{Makefile.in} is left alone.
+
+There can be separate installation prefixes for architecture-specific
+files and architecture-independent files @pxref{Running configure
+Scripts}). @code{configure} substitutes the word @code{exec_prefix} in
+the same way that it does @code{prefix}.
+
+Autoconf @code{configure} scripts replace these two variables without
+requiring them to be enclosed in @samp{@@} characters, and only if they
+have been set, because the Cygnus @code{configure} does so. In
+retrospect, being compatible in this way was a bad decision, because it
+created an inconsistency in Autoconf without giving significant
+benefits.
+
+@node VPATH Substitutions, Automatic Remaking, Installation Prefixes, Makefiles
+@section @code{VPATH} Substitutions
+
+You might want to compile a software package in a different directory
+from the one that contains the source code. Doing this allows you to
+compile the package for several architectures simultaneously from the
+same copy of the source code and keep multiple sets of object files on
+disk.
+
+To support doing this, @code{make} uses the @code{VPATH} variable to
+find the files that are in the source directory. GNU @code{make} and
+most other recent @code{make} programs can do this. Older @code{make}
+programs do not support @code{VPATH}; when using them, the source code
+must be in the same directory as the object files.
+
+To support @code{VPATH}, each @file{Makefile.in} should contain two
+lines that look like:
+
+@example
+srcdir = @@srcdir@@
+VPATH = @@srcdir@@
+@end example
+
+Do not set @code{VPATH} to the value of another variable, for example
+@samp{VPATH = $(srcdir)}, because some versions of @code{make} do not do
+variable substitutions on the value of @code{VPATH}.
+
+@code{configure} substitutes in the correct value for @code{srcdir} when
+it produces @file{Makefile.in}.
+
+Do not use the @code{make} variable @code{$<}, which expands to the
+pathname of the file in the source directory (found with @code{VPATH}),
+except in implicit rules. (An implicit rule is one such as @samp{.c.o},
+which tells how to create a @file{.o} file from a @file{.c} file.) Some
+versions of @code{make} do not set @code{$<} in explicit rules; they
+expand it to an empty value.
+
+Instead, @file{Makefile} command lines should always refer to source
+files by prefixing them with @samp{$(srcdir)/}. For example:
+
+@example
+time.info: time.texinfo
+ $(MAKEINFO) $(srcdir)/time.texinfo
+@end example
+
+@node Automatic Remaking, , VPATH Substitutions, Makefiles
+@section Automatic Remaking
+
+You can put rules like the following in the top-level @file{Makefile.in}
+for a package to automatically update the configuration information when
+you change the configuration files.
+
+@example
+# The next rule also takes care of making config.h from config.h.in.
+# If remaking config.h does not change it, its timestamp is untouched.
+Makefile: Makefile.in config.status
+ $(SHELL) config.status
+config.status: configure
+ $(SHELL) config.status --recheck
+configure: configure.in
+ cd $(srcdir); autoconf
+config.h.in: configure.in
+ cd $(srcdir); autoheader
+@end example
+
+@node Running configure Scripts, Example, Makefiles, Top
+@chapter Running @code{configure} Scripts
+
+A software package that uses a @code{configure} script generated by
+Autoconf should be distributed with a file @file{Makefile.in}, but no
+@file{Makefile}; that way, the user has to properly configure the
+package for the local system before compiling it. Normally, configuring
+consists of simply doing a @code{cd} to the package's source code
+directory and typing:
+
+@example
+configure
+@end example
+
+If the @code{PATH} environment variable does not contain the directory
+@samp{.}, the command is instead:
+
+@example
+./configure
+@end example
+
+Users running @code{csh} on old versions of System V might have to
+explicitly run @code{sh} on @code{configure}:
+
+@example
+sh configure
+@end example
+
+Running @code{configure} takes a minute or two. While it is running, it
+prints some messages that tell what it is doing. If you don't want to
+see the messages, run @code{configure} with its standard output
+redirected to @file{/dev/null}; for example, @samp{./configure >/dev/null}.
+
+To compile the package in a different directory from the one containing
+the source code, you must use a version of @code{make} that supports the
+@code{VPATH} variable, such as GNU @code{make}. @code{cd} to the
+directory where you want the object files and executables to go and run
+@code{configure}. @code{configure} automatically checks for the source
+code in the directory that @code{configure} is in and in @file{..}. If
+for some reason @code{configure} is not in the source code directory
+that you are configuring, then it will report that it can't find the
+source code. In that case, run @code{configure} with the option
+@samp{--srcdir=@var{dir}}, where @var{dir} is the directory that
+contains the source code.
+
+By default, @samp{make install} will install the package's files in
+@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can specify an
+installation prefix other than @file{/usr/local} by giving
+@code{configure} the option @samp{--prefix=@var{path}}. Alternately,
+you can do so by giving a value for the @samp{prefix} variable when you
+run @code{make}, e.g.,
+@example
+make prefix=/usr/gnu
+@end example
+
+You can specify separate installation prefixes for machine-specific
+files and machine-independent files. If you give @code{configure} the
+option @samp{--exec-prefix=@var{path}} or set the @code{make} variable
+@samp{exec_prefix} to @var{path}, the package will use @var{path} as the
+prefix for installing programs and libraries. Normally, all files are
+installed using the same prefix.
+
+Another @code{configure} option is useful mainly in @file{Makefile}
+rules for updating @file{config.status} and @file{Makefile}. The
+@samp{--no-create} option figures out the configuration for your system
+and records it in @file{config.status}, without actually configuring the
+package (creating @file{Makefile}s and perhaps a configuration header
+file). Later, you can run @file{./config.status} to actually configure
+the package. You can also give @file{config.status} the
+@samp{--recheck} option, which makes it re-run @code{configure} with the
+same arguments you used before. This option is useful if you change
+@code{configure}.
+
+Some packages pay attention to @samp{--with-@var{package}} options to
+@code{configure}, where @var{package} is something like @samp{gnu-libc}
+or @samp{x} (for X windows). The README should mention any
+@samp{--with-} options that the package recognizes.
+
+@code{configure} ignores any other arguments that you give it.
+
+On systems that require unusual options for compilation or linking that
+the package's @code{configure} script does not know about, you can give
+@code{configure} initial values for variables by setting them in the
+environment. In Bourne-compatible shells, you can do that on the
+command line like this:
+
+@example
+CC='gcc -traditional' LIBS=-lposix ./configure
+@end example
+
+The @code{make} variables that you might want to override with
+environment variables when running @code{configure} are:
+
+(For these variables, any value given in the environment overrides the
+value that @code{configure} would choose:)
+
+@defvar CC
+C compiler program. The default is @code{cc}, or @code{gcc} if
+@code{gcc} is in your @code{PATH}.
+@end defvar
+
+@defvar INSTALL
+Program to use to install files. The default is @code{install} if you
+have it, @code{cp} otherwise.
+@end defvar
+
+(For these variables, any value given in the environment is added to
+the value that @code{configure} chooses:)
+
+@defvar DEFS
+Configuration options, in the form @samp{-Dfoo -Dbar@dots{}}. Do not
+use this variable in packages that use @code{AC_CONFIG_HEADER}.
+@end defvar
+
+@defvar LIBS
+Libraries to link with, in the form @samp{-lfoo -lbar@dots{}}.
+@end defvar
+
+Of course, in the long term, most problems requiring manual intervention
+should be fixed by updating either the Autoconf macros or the
+@file{configure.in} file for that package. @xref{Making configure
+Scripts}, for a discussion of that subject.
+
+@node Example, Preprocessor Symbol Index, Running configure Scripts, Top
+@chapter An Example
+
+Here are sample @file{configure.in} and @file{Makefile.in} files, to
+give a real illustration of using Autoconf. They are from the GNU
+@code{cpio} package, which also includes the @code{mt} and @code{rmt}
+programs. This package does not use a configuration header file; it
+passes @samp{-D} options to the C compiler on the command line.
+
+@menu
+* Sample configure.in:: An example of a @file{configure} template.
+* Sample Makefile.in:: An example of a @file{Makefile} template.
+@end menu
+
+@node Sample configure.in, Sample Makefile.in, , Example
+@section Sample @file{configure.in}
+
+@noindent
+Here is @file{configure.in} from GNU @code{cpio}. The @code{dnl} macro
+after @code{AC_SUBST} is suppresses an extra (though harmless) newline
+in the generated @code{configure} script (because the @code{AC_SUBST}
+macro does not produce any output where it is called).
+
+@example
+dnl Process this file with autoconf to produce a configure script.
+AC_INIT(cpio.h)
+PROGS="cpio"
+AC_SUBST(PROGS)dnl
+AC_PROG_CC
+AC_PROG_CPP
+AC_GCC_TRADITIONAL
+AC_PROG_INSTALL
+AC_AIX
+AC_MINIX
+AC_ISC_POSIX
+AC_RETSIGTYPE
+AC_MAJOR_HEADER
+AC_REMOTE_TAPE
+test -n "$have_mtio" && PROGS="$PROGS mt"
+AC_RSH
+AC_CONST
+AC_UID_T
+AC_STDC_HEADERS
+AC_UNISTD_H
+AC_HAVE_HEADERS(string.h fcntl.h utime.h sys/io/trioctl.h)
+AC_REPLACE_FUNCS(fnmatch bcopy mkdir strdup)
+AC_HAVE_FUNCS(strerror lchown)
+AC_VPRINTF
+AC_ALLOCA
+AC_XENIX_DIR
+AC_HAVE_LIBRARY(socket, [LIBS="$LIBS -lsocket"])
+AC_HAVE_LIBRARY(nsl, [LIBS="$LIBS -lnsl"])
+AC_OUTPUT(Makefile)
+@end example
+
+@node Sample Makefile.in, , Sample configure.in, Example
+@section Sample @file{Makefile.in}
+
+@noindent
+Here is @file{Makefile.in} from GNU @code{cpio}, with some irrelevant
+lines omitted, for brevity.
+
+@example
+srcdir = @@srcdir@@
+VPATH = @@srcdir@@
+
+CC = @@CC@@
+
+INSTALL = @@INSTALL@@
+INSTALL_PROGRAM = @@INSTALL_PROGRAM@@
+INSTALL_DATA = @@INSTALL_DATA@@
+
+DEFS = @@DEFS@@
+LIBS = @@LIBS@@
+RTAPELIB = @@RTAPELIB@@
+
+CFLAGS = -g
+LDFLAGS = -g
+
+prefix = /usr/local
+exec_prefix = $(prefix)
+binprefix =
+manprefix =
+
+bindir = $(exec_prefix)/bin
+libdir = $(exec_prefix)/lib
+mandir = $(prefix)/man/man1
+manext = 1
+
+SHELL = /bin/sh
+
+SRCS = copyin.c copyout.c copypass.c defer.c dstring.c global.c \
+main.c tar.c util.c error.c getopt.c getopt1.c filemode.c version.c \
+rtapelib.c dirname.c idcache.c makepath.c xmalloc.c stripslash.c \
+userspec.c xstrdup.c bcopy.c fnmatch.c mkdir.c strdup.c
+OBJS = copyin.o copyout.o copypass.o defer.o dstring.o global.o \
+main.o tar.o util.o error.o getopt.o getopt1.o filemode.o version.o \
+$(RTAPELIB) dirname.o idcache.o makepath.o xmalloc.o stripslash.o \
+userspec.o xstrdup.o @@LIBOBJS@@ @@ALLOCA@@
+# mt source files not shared with cpio.
+MT_SRCS = mt.c argmatch.c
+MT_OBJS = mt.o argmatch.o error.o getopt.o getopt1.o \
+xmalloc.o version.o $(RTAPELIB) @@ALLOCA@@
+HDRS = cpio.h cpiohdr.h tar.h tarhdr.h defer.h dstring.h extern.h filetypes.h \
+system.h fnmatch.h getopt.h rmt.h
+DISTFILES = $(SRCS) $(HDRS) COPYING COPYING.LIB ChangeLog Makefile.in \
+README NEWS INSTALL cpio.1 mt.1 makefile.pc makefile.os2 cpio.def \
+configure configure.in mkinstalldirs $(MT_SRCS) rmt.c tcexparg.c alloca.c
+
+all: @@PROGS@@
+
+.c.o:
+ $(CC) -c $(CPPFLAGS) $(DEFS) -I$(srcdir) $(CFLAGS) $<
+
+install: installdirs all $(srcdir)/cpio.1 $(srcdir)/mt.1
+ $(INSTALL_PROGRAM) cpio $(bindir)/$(binprefix)cpio
+ test ! -f mt || $(INSTALL_PROGRAM) mt $(bindir)/$(binprefix)mt
+ -test ! -f rmt || $(INSTALL_PROGRAM) rmt $(libdir)/rmt
+ $(INSTALL_DATA) $(srcdir)/cpio.1 $(mandir)/$(manprefix)cpio.$(manext)
+ test ! -f mt || \
+ $(INSTALL_DATA) $(srcdir)/mt.1 $(mandir)/$(manprefix)mt.$(manext)
+
+installdirs:
+ $(srcdir)/mkinstalldirs $(bindir) $(libdir) $(mandir)
+
+uninstall:
+ cd $(bindir); rm -f $(binprefix)cpio $(binprefix)mt
+ -rm -f $(libdir)/rmt
+ cd $(mandir); rm -f $(manprefix)cpio.$(manext) $(manprefix)mt.$(manext)
+
+check:
+ @@echo No tests are supplied.
+
+cpio: $(OBJS)
+ $(CC) $(LDFLAGS) -o $@@ $(OBJS) $(LIBS)
+
+rmt: rmt.o
+ $(CC) $(LDFLAGS) -o $@@ rmt.o $(LIBS)
+
+mt: $(MT_OBJS)
+ $(CC) $(LDFLAGS) -o $@@ $(MT_OBJS) $(LIBS)
+
+Makefile: Makefile.in config.status
+ $(SHELL) config.status
+config.status: configure
+ $(SHELL) config.status --recheck
+configure: configure.in
+ cd $(srcdir); autoconf
+
+TAGS: $(SRCS)
+ etags $(SRCS)
+
+clean:
+ rm -f cpio rmt mt *.o core
+
+mostlyclean: clean
+
+distclean: clean
+ rm -f Makefile config.status
+
+realclean: distclean
+ rm -f TAGS
+
+dist: $(DISTFILES)
+ echo cpio-`sed -e '/version_string/!d' \
+ -e 's/[^0-9.]*\([0-9.]*\).*/\1/' -e q version.c` > .fname
+ rm -rf `cat .fname`
+ mkdir `cat .fname`
+ -ln $(DISTFILES) `cat .fname`
+ for file in $(DISTFILES); do \
+ test -r `cat .fname`/$$file || cp -p $$file `cat .fname`; \
+ done
+ tar chzf `cat .fname`.tar.gz `cat .fname`
+ rm -rf `cat .fname` .fname
+@end example
+
+@node Preprocessor Symbol Index, Macro Index, Example, Top
+@unnumbered Preprocessor Symbol Index
+
+This is an alphabetical list of the C preprocessor symbols that the
+Autoconf macros define. To work with Autoconf, C source code needs to
+use these names in @code{#if} directives.
+
+@printindex vr
+
+@node Macro Index, , Preprocessor Symbol Index, Top
+@unnumbered Macro Index
+
+This is an alphabetical list of the Autoconf macros. To make the list
+easier to use, the macros are listed without their preceding @samp{AC_}.
+
+@printindex fn
+
+@contents
+@bye
+
+@c Local variables:
+@c compile-command: "makeinfo --no-split autoconf.texi"
+@c End:
--- /dev/null
+\input texinfo @c -*-texinfo-*-
+@c %**start of header
+@setfilename autoconf.info
+@settitle Autoconf
+@setchapternewpage odd
+@c %**end of header
+@c Use on instead of odd in the setchapternewpage for single-sided printing.
+
+@set EDITION 1.6
+@set VERSION 1.6
+@set UPDATED August 1993
+
+@iftex
+@finalout
+@end iftex
+
+@ifinfo
+This file documents the GNU Autoconf package for creating scripts to
+configure source code packages using templates and an @code{m4} macro
+package.
+
+Copyright (C) 1992, 1993 Free Software Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+
+@ignore
+Permission is granted to process this file through TeX and print the
+results, provided the printed document carries copying permission
+notice identical to this one except for the removal of this paragraph
+(this paragraph not being relevant to the printed manual).
+
+@end ignore
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
+@end ifinfo
+
+@titlepage
+@title Autoconf
+@subtitle Generating Automatic Configuration Scripts
+@subtitle Edition @value{EDITION}, for Autoconf version @value{VERSION}
+@subtitle @value{UPDATED}
+@author by David MacKenzie, Roland McGrath, and Noah Friedman
+
+@page
+@vskip 0pt plus 1filll
+Copyright @copyright{} 1992, 1993 Free Software Foundation, Inc.
+
+Permission is granted to make and distribute verbatim copies of
+this manual provided the copyright notice and this permission notice
+are preserved on all copies.
+
+Permission is granted to copy and distribute modified versions of this
+manual under the conditions for verbatim copying, provided that the entire
+resulting derived work is distributed under the terms of a permission
+notice identical to this one.
+
+Permission is granted to copy and distribute translations of this manual
+into another language, under the above conditions for modified versions,
+except that this permission notice may be stated in a translation approved
+by the Foundation.
+@end titlepage
+
+@node Top, Introduction, , (dir)
+@comment node-name, next, previous, up
+
+@ifinfo
+This file documents the GNU Autoconf package for creating scripts to
+configure source code packages using templates and an @code{m4} macro
+package. This is edition @value{EDITION}, for Autoconf version @value{VERSION}.
+
+@end ifinfo
+
+@menu
+* Introduction:: Autoconf's purpose, strengths, and weaknesses.
+* Distributing:: Legal restrictions on Autoconf output.
+* Making configure Scripts:: How to organize and produce Autoconf scripts.
+* Specific Tests:: Macros that check for particular features.
+* General Purpose Macros:: Macros that check for kinds of features.
+* Writing Macros:: How to add your own macros to Autoconf.
+* Makefiles:: Information Autoconf uses in @file{Makefile}s.
+* Running configure Scripts:: How to use the Autoconf output.
+* Example:: Sample Autoconf input files.
+* Preprocessor Symbol Index:: Index of C preprocessor symbols defined.
+* Macro Index:: Index of Autoconf macros.
+@end menu
+
+@node Introduction, Distributing, Top, Top
+@chapter Introduction
+
+Autoconf is a tool for producing shell scripts that automatically
+configure software source code packages to adapt to many kinds of
+UNIX-like systems. The configuration scripts produced by Autoconf are
+independent of Autoconf when they are run, so their users do not need to
+have Autoconf.
+
+The configuration scripts produced by Autoconf normally require no
+manual user intervention when run; they do not even take an argument
+specifying the system type. Instead, they test for the presence of each
+feature that the software package they are for might need individually.
+(Before each check, they print a one-line message stating what they are
+checking for, so the user doesn't get too bored while waiting for the
+script to finish.) As a result, they deal well with systems that are
+hybrids or customized from the more common UNIX variants. There is no
+need to maintain files that list the features supported by each release
+of each variant of UNIX.
+
+For each software package that Autoconf is used with, it creates a
+configuration script from a template file that lists the operating
+system features that the package can use. After the shell code to
+recognize and respond to an operating system feature has been written,
+Autoconf allows it to be shared by many software packages that can
+use (or need) that feature. If it later turns out that the shell code
+needs adjustment for some reason, it needs to be changed in only one
+place; all of the the configuration scripts can be regenerated
+automatically to take advantage of the updated code.
+
+Larry Wall's Metaconfig package is similar in purpose to Autoconf, but
+is more general. The scripts it produces require manual user
+intervention, which is quite inconvenient when configuring large source
+trees.
+
+Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling,
+if some care is taken in writing them. They should avoid executing test
+programs, since test programs compiled with a cross-compiler can not be
+executed on the host system. Also, they shouldn't do anything that
+tests features of the host system instead of the target system.
+
+Autoconf imposes some restrictions on the names of macros used with
+@code{#ifdef} in C programs (@pxref{Preprocessor Symbol Index}).
+
+Autoconf requires GNU @code{m4} in order to generate the scripts. It
+uses features that some UNIX versions of @code{m4} do not have; it is
+also reported to overflow internal limits of some versions of @code{m4}.
+
+Autoconf does not work well with GNU C library releases before 1.06.
+The GNU C library contains stubs (which always return an error) for
+functions that are not available instead of omitting them from the
+library. As a result, Autoconf scripts are fooled into thinking that
+those functions are available. This problem does not exist with
+releases 1.06 and later of the GNU C library, which define C
+preprocessor macros that the Autoconf macros @code{AC_FUNC_CHECK} and
+@code{AC_REPLACE_FUNCS} test, indicating that certain functions are
+stubs (@pxref{General Tests}, for more information on checking for
+functions).
+
+@ifinfo
+Autoconf was written by David MacKenzie, with help from Franc,ois
+@end ifinfo
+@tex
+Autoconf was written by David MacKenzie, with help from Fran\c cois
+@end tex
+Pinard, Karl Berry, Richard Pixley, Ian Lance Taylor, Roland McGrath,
+and Noah Friedman. It was inspired by Brian Fox's automatic
+configuration system for BASH, by Larry Wall's Metaconfig, and by
+Richard Stallman, Richard Pixley, and John Gilmore's configuration tools
+for the GNU compiler and object file utilities.
+
+Mail suggestions and bug reports for Autoconf to
+@code{bug-gnu-utils@@prep.ai.mit.edu}. Please include the Autoconf version
+number, which you can get by running @samp{autoconf --version}.
+
+@node Distributing, Making configure Scripts, Introduction, Top
+@chapter Distributing Autoconf Output
+
+The configuration scripts that Autoconf produces are covered by the GNU
+General Public License. This is because they consist almost entirely of
+parts of Autoconf itself, rearranged somewhat, and Autoconf is
+distributed under the terms of the GPL. As applied to Autoconf,
+the GPL just means that you need to distribute @file{configure.in} along
+with @file{configure}.
+
+Programs that use Autoconf scripts to configure themselves do not
+automatically come under the GPL. Distributing an Autoconf
+configuration script as part of a program is considered to be @emph{mere
+aggregation} of that work with the Autoconf script. Such programs are
+not derivative works based on Autoconf; only their configuration scripts
+are. We still encourage software authors to distribute their work under
+terms like those of the GPL, but doing so is not required to use
+Autoconf.
+
+@node Making configure Scripts, Specific Tests, Distributing, Top
+@chapter Making @code{configure} Scripts
+
+The configuration scripts that Autoconf produces are by convention
+called @code{configure} when they are distributed. When run, they
+create several files:
+
+@itemize @bullet
+@item
+one or more @file{Makefile} files (one in each subdirectory of the
+package), from template @file{Makefile.in} files (@pxref{Makefiles});
+
+@item
+optionally, a C header file, the name of which is configurable,
+containing @code{#define} statements;
+
+@item
+a shell script called @file{config.status} that, when run, will recreate
+the current configuration parameter settings.
+@end itemize
+
+To create a @code{configure} script with Autoconf, you need to write an
+Autoconf input file and run Autoconf on it to produce the script. And,
+of course, test the resulting script.
+
+Here is a diagram showing how the files that can be used in
+configuration are produced:
+
+@example
+acgeneral.m4 \ Makefile.in \
+acspecific.m4 \ \
+autoconf* -> m4* -> configure* -> config.status* -> Makefile \
+configure.in / | | \
+ | | | | make* -> your
+ | | | | /package
+ | | config.status* -> config.h /
+configure.in \ /
+autoheader* -> - - - - - - - - - - -> config.h.in /
+acconfig.h /
+@end example
+
+@noindent
+Executables are suffixed by @samp{*}, while files appearing twice are
+linked with lines of @samp{|}.
+
+@menu
+* Writing configure.in:: What to put in an Autoconf input file.
+* Invoking autoconf:: How to create configuration scripts.
+* Invoking autoheader:: How to create configuration header files.
+@end menu
+
+@node Writing configure.in, Invoking autoconf, , Making configure Scripts
+@section Writing @file{configure.in}
+
+To produce a @code{configure} script for a software package, create a
+file called @file{configure.in} that contains invocations of the
+Autoconf macros that test the system features your package needs or can
+use. Autoconf macros already exist to check for many features; see
+@ref{Specific Tests}, for their descriptions. For most other
+features, you can use Autoconf template macros to produce custom checks;
+see @ref{General Tests}, for information about them. For especially
+tricky or specialized features, @file{configure.in} might need to
+contain some hand-crafted shell commands. @xref{Writing Macros}, for
+guidelines on writing tests from scratch.
+
+Every @file{configure.in} must begin with a call to @code{AC_INIT} and
+end with a call to @code{AC_OUTPUT} (@pxref{Setup}). Other than that,
+the order in which @file{configure.in} calls the Autoconf macros is
+generally not important, except that some macros rely on other macros
+having been called first, because they check previously set values of
+some variables to decide what to do. These macros are noted in the
+individual descriptions (@pxref{Specific Tests}).
+
+To encourage consistency, here is a suggested order for calling the
+Autoconf macros. A few macros need to be called in a different order
+from the one given here; they are noted in their individual descriptions
+(@pxref{Specific Tests}). Note that there must not be any space
+between the macro name and the open parentheses.
+
+@display
+@group
+@code{AC_INIT(@var{file})}
+checks for programs
+checks for UNIX variants that set @code{DEFS}
+checks for header files
+checks for typedefs
+checks for functions
+checks for structure members
+checks for compiler characteristics
+checks for operating system services
+other checks for UNIX variants
+@code{AC_OUTPUT(@r{[}@var{file@dots{}}@r{]})}
+@end group
+@end display
+
+You can include comments in @file{configure.in} files by starting them
+with the @code{m4} predefined macro @code{dnl}, which discards text up
+through the next newline. These comments do not appear in the generated
+@code{configure} scripts. For example, it is helpful to begin
+@file{configure.in} files with a line like this:
+
+@example
+dnl Process this file with autoconf to produce a configure script.
+@end example
+
+@xref{Sample configure.in}, for an example of a real @file{configure.in}
+script.
+
+@node Invoking autoconf, Invoking autoheader, Writing configure.in, Making configure Scripts
+@section Invoking @code{autoconf}
+
+To create @code{configure} from @file{configure.in}, run the
+@code{autoconf} program with no arguments. @code{autoconf} processes
+@file{configure.in} with the @code{m4} macro processor, using the
+Autoconf macros. If you give @code{autoconf} an argument, it reads that
+file instead of @file{configure.in} and writes the configuration script
+to the standard output instead of to @file{configure}. If you give
+@code{autoconf} the argument @samp{-}, it reads the standard input
+instead of @file{configure.in} and writes the configuration script on
+the standard output.
+
+The Autoconf macros are defined in two or more files. Two of the files
+are distributed with Autoconf: @file{acgeneral.m4} (@pxref{General
+Purpose Macros}) and @file{acspecific.m4} (@pxref{Specific Tests}).
+@code{autoconf} also looks for an optional file called @file{aclocal.m4}
+both in the directory that contains other installed Autoconf macro files and
+in the current directory. (If both files exist, it uses both of them.)
+Those files can contain your site's own locally written Autoconf macro
+definitions. @xref{Writing Macros}, for more information.
+
+You can override the directory where @code{autoconf} looks for the
+installed macro files by setting the @code{AC_MACRODIR} environment
+variable to a different directory. You can also give @code{autoconf}
+the @samp{--macrodir} option, which overrides @code{AC_MACRODIR}.
+
+@code{autoconf} also accepts the options @code{--version}, which prints
+the Autoconf version number and exits, and @code{--help}, which prints a
+summary of the command-line options and exits.
+
+@node Invoking autoheader, , Invoking autoconf, Making configure Scripts
+@section Invoking @code{autoheader}
+
+You can use the program @code{autoheader} to create a template file of C
+@samp{#define} statements for @code{configure} to use. By default, the
+file that @code{autoheader} creates is called @file{config.h.in}; if
+@file{configure.in} invokes @code{AC_CONFIG_HEADER(@var{file})},
+@code{autoheader} creates @file{@var{file}.in}.
+
+@code{autoheader} scans @file{configure.in} and figures out which C
+preprocessor symbols it might define. It copies comments and
+@code{#define} and @code{#undef} statements from a file called
+@file{acconfig.h}, which comes with and is installed with Autoconf; it
+also uses a file called @file{acconfig.h} in the current directory, if
+present. For symbols that @code{AC_HAVE_HEADERS} or
+@code{AC_HAVE_FUNCS} define, @code{autoheader} generates comments and
+@code{#undef} statements itself rather than copying them from a file,
+since the possible symbols are effectively limitless.
+
+The file that @code{autoheader} creates contains only @code{#define} and
+@code{#undef} statements and their accompanying comments; there is no
+provision in @code{autoheader} for adding other code or comments to the
+file.
+
+If you give @code{autoheader} an argument, it uses that file instead of
+@file{configure.in} and writes the header file to the standard output
+instead of to @file{config.h.in}. If you give @code{autoheader} an
+argument of @samp{-}, it reads the standard input instead of
+@file{configure.in} and writes the header file to the standard output.
+
+You can override the directory where @code{autoheader} looks for the
+installed macro and @file{acconfig.h} files by setting the
+@code{AC_MACRODIR} environment variable to a different directory. You
+can also give @code{autoheader} the @samp{--macrodir} option, which
+overrides @code{AC_MACRODIR}.
+
+@code{autoheader} also accepts the options @code{--version}, which prints
+the Autoconf version number and exits, and @code{--help}, which prints a
+summary of the command-line options and exits.
+
+@node Specific Tests, General Purpose Macros, Making configure Scripts, Top
+@chapter Specific Tests
+
+These macros test for particular operating system features that packages
+might need or want to use. If you need to test for a feature that none
+of these macros check for, you can probably do it by calling one of the
+general purpose test macros with appropriate arguments (@pxref{General
+Tests}).
+
+All of these macros that set @code{make} variables call @code{AC_SUBST}
+on those variables (@pxref{Setting Variables}, for details about
+@code{AC_SUBST}). The phrase ``define @var{name}'' is used below as a
+shorthand to mean either add @samp{-D@var{name}=1} to the @code{make}
+variable @code{DEFS}, or put @samp{#define @var{name} 1} in the
+configuration header file, depending on whether @code{AC_CONFIG_HEADER} has
+been called. @xref{Setting Variables}, for more information.
+
+Within each section below, the macros are listed in alphabetical order.
+The macros are generally named for the @code{make} variables or C
+preprocessor macros that they define; those names are based largely on
+what existing GNU programs use. These macros are defined in the file
+@file{acspecific.m4}.
+
+@menu
+* Alternative Programs:: Selecting between alternative programs.
+* Header Files:: Header files that might be missing.
+* Typedefs:: @code{typedef}s that might be missing.
+* Library Functions:: C library functions that might be missing.
+* Structures:: Structures or members that might be missing.
+* Compiler Characteristics:: C compiler or machine architecture features.
+* System Services:: Operating system services.
+* UNIX Variants:: Special cases for specific UNIX variants.
+@end menu
+
+@node Alternative Programs, Header Files, , Specific Tests
+@section Alternative Programs
+
+The following macros check for the presence or behavior of particular
+programs:
+
+@defmac AC_DECLARE_YYTEXT
+@findex DECLARE_YYTEXT
+@vindex DECLARE_YYTEXT
+Define @code{DECLARE_YYTEXT} to declare @code{yytext} appropriately,
+depending on whether @code{lex} or @code{flex} is being used. This
+macro calls @code{AC_PROG_CPP} and @code{AC_PROG_LEX} if they haven't
+been called already.
+@end defmac
+
+@defmac AC_LN_S
+@findex LN_S
+If @samp{ln -s} works on the current filesystem (the O.S. and filesystem
+support symbolic links), set shell and @code{make} variable @code{LN_S}
+to @samp{ln -s}, otherwise set it to @samp{ln}.
+@end defmac
+
+@defmac AC_MINUS_C_MINUS_O
+@findex MINUS_C_MINUS_O
+@vindex NO_MINUS_C_MINUS_O
+If the C compiler does not accept the @samp{-c} and @samp{-o} options
+simultaneously, define @code{NO_MINUS_C_MINUS_O}.
+@end defmac
+
+@defmac AC_PROG_YACC
+@findex PROG_YACC
+If @code{bison} is found, set @code{make} variable @code{YACC} to
+@samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC}
+to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}.
+@end defmac
+
+@defmac AC_PROG_CPP
+@findex PROG_CPP
+Set shell and @code{make} variable @code{CPP} to a command that runs the
+C preprocessor. If @samp{$CC -E} doesn't work, it uses @file{/lib/cpp}.
+
+Many of the specific test macros use the value of @code{CPP} indirectly
+by calling @code{AC_TEST_CPP}, @code{AC_HEADER_CHECK},
+@code{AC_HEADER_EGREP}, or @code{AC_PROGRAM_EGREP}. Those macros call
+this macro first if it hasn't been called already. It should be called
+after @code{AC_PROG_CC}.
+@end defmac
+
+@defmac AC_PROG_LEX
+@findex PROG_LEX
+If @code{flex} is found, set @code{make} variable @code{LEX} to
+@samp{flex} and @code{LEXLIB} to @samp{-lfl}, if that library is in a
+standard place. Otherwise set @code{LEX} to @samp{lex} and
+@code{LEXLIB} to @samp{-ll}.
+@end defmac
+
+@defmac AC_PROG_AWK
+@findex PROG_AWK
+Check for @code{mawk}, @code{gawk}, @code{nawk}, and @code{awk}, in that
+order, and set @code{make} variable @code{AWK} to the first one that it
+finds.
+@end defmac
+
+@defmac AC_PROG_CC
+@findex PROG_CC
+If @code{gcc} is found, set @code{make} variable @code{CC} to @samp{gcc},
+and set shell variable @code{GCC} to 1 for use by macros such as
+@code{AC_GCC_TRADITIONAL}.
+@end defmac
+
+@defmac AC_GCC_TRADITIONAL
+@findex GCC_TRADITIONAL
+Add @samp{-traditional} to @code{make} variable @code{CC} if using the
+GNU C compiler and @code{ioctl} does not work properly without
+@samp{-traditional}. This macro calls @code{AC_PROG_CC} and
+@code{AC_PROG_CPP} if they haven't been called already.
+@end defmac
+
+@defmac AC_PROG_INSTALL
+@findex PROG_INSTALL
+Set @code{make} variable @code{INSTALL} to @samp{install -c} if
+@code{install} is found, otherwise set it to @samp{cp}. Screens out the
+false matches @file{/etc/install}, @file{/usr/sbin/install}, and other
+instances of @code{install} known not to work. The variable
+@code{INSTALL_PROGRAM} is set to @samp{$(INSTALL)} and
+@code{INSTALL_DATA} is set to @samp{$(INSTALL) -m 644}.
+@end defmac
+
+@defmac AC_PROG_RANLIB
+@findex PROG_RANLIB
+Set @code{make} variable @code{RANLIB} to @samp{ranlib} if @code{ranlib}
+is found, otherwise to @samp{:} (do nothing).
+@end defmac
+
+@defmac AC_RSH
+@findex RSH
+@vindex NO_REMOTE
+@vindex HAVE_NETDB_H
+If a remote shell is available, put @samp{rtapelib.o} in @code{make}
+variable @code{RTAPELIB}. Otherwise, also do so if @file{netdb.h}
+exists (implying the @code{rexec} function), and in addition define
+@code{HAVE_NETDB_H}. If neither a remote shell nor @code{rexec} is
+available, define @code{NO_REMOTE}.
+@end defmac
+
+@node Header Files, Typedefs, Alternative Programs, Specific Tests
+@section Header Files
+
+The following macros check for the presence of certain C header files:
+
+@defmac AC_DIR_HEADER
+@findex DIR_HEADER
+@vindex DIRENT
+@vindex SYSDIR
+@vindex SYSNDIR
+@vindex NDIR
+@vindex VOID_CLOSEDIR
+If the system has @file{dirent.h}, define @code{DIRENT}; otherwise, if
+it has @file{sys/ndir.h}, define @code{SYSNDIR}; otherwise, if it has
+@file{sys/dir.h}, define @code{SYSDIR}; otherwise, if it has
+@file{ndir.h}, define @code{NDIR}. Also, if the directory library
+header file contains a declaration of the @code{closedir} function with
+a @code{void} return type, define @code{VOID_CLOSEDIR}. The directory
+library declarations in the source code should look something like the
+following:
+
+@example
+@group
+/* unistd.h defines _POSIX_VERSION on POSIX.1 systems. */
+#if defined(DIRENT) || defined(_POSIX_VERSION)
+#include <dirent.h>
+#define NLENGTH(dirent) (strlen((dirent)->d_name))
+#else /* not (DIRENT or _POSIX_VERSION) */
+#define dirent direct
+#define NLENGTH(dirent) ((dirent)->d_namlen)
+#ifdef SYSNDIR
+#include <sys/ndir.h>
+#endif /* SYSNDIR */
+#ifdef SYSDIR
+#include <sys/dir.h>
+#endif /* SYSDIR */
+#ifdef NDIR
+#include <ndir.h>
+#endif /* NDIR */
+#endif /* not (DIRENT or _POSIX_VERSION) */
+@end group
+@end example
+
+Using the above declarations, the program would declare variables to be
+type @code{struct dirent}, not @code{struct direct}, and would access
+the length of a directory entry name by passing a pointer to a
+@code{struct dirent} to the @code{NLENGTH} macro.
+@end defmac
+
+@defmac AC_MAJOR_HEADER
+@findex MAJOR_HEADER
+@vindex MAJOR_IN_MKDEV
+@vindex MAJOR_IN_SYSMACROS
+If @file{sys/types.h} does not define @code{major}, @code{minor}, and
+@code{makedev}, but @file{sys/mkdev.h} does, define
+@code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define
+@code{MAJOR_IN_SYSMACROS}.
+@end defmac
+
+@defmac AC_MEMORY_H
+@findex MEMORY_H
+@vindex NEED_MEMORY_H
+Define @code{NEED_MEMORY_H} if @code{memcpy}, @code{memcmp}, etc. are
+not declared in @file{string.h} and @file{memory.h} exists. This macro
+is obsolete; instead, use @code{AC_HAVE_HEADERS(memory.h)}. See the
+example for @code{AC_STDC_HEADERS}.
+@end defmac
+
+@defmac AC_STDC_HEADERS
+@findex STDC_HEADERS
+@vindex STDC_HEADERS
+Define @code{STDC_HEADERS} if the system has ANSI C header files.
+Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h},
+@file{string.h}, and @file{float.h}; if the system has
+those, it probably has the rest of the ANSI C header files. This macro
+also checks whether @file{string.h} declares @code{memchr} (and
+thus presumably the other @code{mem} functions) and whether the
+@file{ctype.h} macros work on characters with the high bit set,
+as ANSI C requires.
+
+Use @code{STDC_HEADERS} instead of @code{__STDC__} to determine whether
+the system has ANSI-compliant header files (and probably C library
+functions) because many systems that have GCC do not have ANSI C header
+files.
+
+To check whether to use the System V/ANSI C string functions and header
+file, you can put the following in @file{configure.in}:
+
+@example
+AC_STDC_HEADERS
+AC_HAVE_HEADERS(string.h memory.h)
+@end example
+
+@noindent
+Then, in the code, use a test like this:
+
+@example
+@group
+#if STDC_HEADERS || HAVE_STRING_H
+#include <string.h>
+/* An ANSI string.h and pre-ANSI memory.h might conflict. */
+#if !STDC_HEADERS && HAVE_MEMORY_H
+#include <memory.h>
+#endif /* not STDC_HEADERS and HAVE_MEMORY_H */
+#define index strchr
+#define rindex strrchr
+#define bcopy(s, d, n) memcpy ((d), (s), (n))
+#define bcmp(s1, s2, n) memcmp ((s1), (s2), (n))
+#define bzero(s, n) memset ((s), 0, (n))
+#else /* not STDC_HEADERS and not HAVE_STRING_H */
+#include <strings.h>
+/* memory.h and strings.h conflict on some systems. */
+#endif /* not STDC_HEADERS and not HAVE_STRING_H */
+@end group
+@end example
+
+@noindent
+This example asssumes that your code uses the BSD style functions. If
+you use the System V/ANSI C style functions, you will need to replace
+the macro definitions with ones that go in the other direction.
+@end defmac
+
+@defmac AC_UNISTD_H
+@findex UNISTD_H
+@vindex HAVE_UNISTD_H
+Define @code{HAVE_UNISTD_H} if the system has @file{unistd.h}. The way
+to check if the system supports POSIX.1 is:
+
+@example
+@group
+#if HAVE_UNISTD_H
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+#ifdef _POSIX_VERSION
+/* Code for POSIX.1 systems. */
+#endif
+@end group
+@end example
+
+@vindex _POSIX_VERSION
+@code{_POSIX_VERSION} is defined when @file{unistd.h} is included on
+POSIX.1 systems. If there is no @file{unistd.h}, it is definitely not a
+POSIX.1 system. However, some non-POSIX.1 systems do have @file{unistd.h}.
+@end defmac
+
+@defmac AC_USG
+@findex USG
+@vindex USG
+Define @code{USG} if the system does not have @file{strings.h},
+@code{rindex}, @code{bzero}, etc. This implies that it has
+@file{string.h}, @code{strrchr}, @code{memset}, etc.
+
+The symbol @code{USG} is obsolete. Instead of this macro, use
+@code{AC_HAVE_HEADERS(string.h)} and use @code{HAVE_STRING_H} in your
+code. See the example for @code{AC_STDC_HEADERS}.
+@end defmac
+
+@node Typedefs, Library Functions, Header Files, Specific Tests
+@section Typedefs
+
+The following macros check for predefined C types:
+
+@defmac AC_GETGROUPS_T
+@findex GETGROUPS_T
+@vindex GETGROUPS_T
+Define @code{GETGROUPS_T} to be whichever of @code{gid_t} or @code{int}
+is the base type of the array argument to @code{getgroups}.
+@end defmac
+
+@defmac AC_MODE_T
+@findex MODE_T
+@vindex mode_t
+If @code{mode_t} is not defined in @file{sys/types.h}, define
+@code{mode_t} to be @code{int}.
+@end defmac
+
+@defmac AC_OFF_T
+@findex OFF_T
+@vindex off_t
+If @code{off_t} is not defined in @file{sys/types.h}, define
+@code{off_t} to be @code{long}.
+@end defmac
+
+@defmac AC_PID_T
+@findex PID_T
+@vindex pid_t
+If @code{pid_t} is not defined in @file{sys/types.h}, define
+@code{pid_t} to be @code{int}.
+@end defmac
+
+@defmac AC_RETSIGTYPE
+@findex RETSIGTYPE
+@vindex RETSIGTYPE
+If @file{signal.h} declares @code{signal} as returning a pointer to a
+function returning @code{void}, define @code{RETSIGTYPE} to be
+@code{void}; otherwise, define it to be @code{int}.
+
+Define signal handlers as returning type @code{RETSIGTYPE}:
+
+@example
+@group
+RETSIGTYPE
+hup_handler ()
+@{
+@dots{}
+@}
+@end group
+@end example
+@end defmac
+
+@defmac AC_SIZE_T
+@findex SIZE_T
+@vindex size_t
+If @code{size_t} is not defined in @file{sys/types.h}, define
+@code{size_t} to be @code{unsigned}.
+@end defmac
+
+@defmac AC_UID_T
+@findex UID_T
+@vindex uid_t
+@vindex gid_t
+If @code{uid_t} is not defined in @file{sys/types.h}, define
+@code{uid_t} to be @code{int} and @code{gid_t} to be @code{int}.
+@end defmac
+
+@node Library Functions, Structures, Typedefs, Specific Tests
+@section Library Functions
+
+The following macros check for particular C library functions:
+
+@defmac AC_ALLOCA
+@findex ALLOCA
+@vindex HAVE_ALLOCA_H
+Check how to get @code{alloca}. Tries to get a builtin version by
+checking for @file{alloca.h} or the predefined C preprocessor macros
+@code{__GNUC__} and @code{_AIX}. If that fails, it looks for a function
+in the standard C library. If that fails, it sets the @code{make}
+variable @code{ALLOCA} to @samp{alloca.o}. This variable is separate
+from @code{LIBOBJS} so multiple programs can share the value of
+@code{ALLOCA} without needing to create an actual library.
+
+If this macro finds @file{alloca.h}, it defines @code{HAVE_ALLOCA_H}.
+
+This macro does not try to get @code{alloca} from the SVR3 @file{libPW}
+or the SVR4 @file{libucb} because those libraries contain some
+incompatible functions that cause trouble. Some versions do not even
+contain @code{alloca} or contain a buggy version. If you still want to
+use their @code{alloca}, use @code{ar} to extract @file{alloca.o} from
+them instead of compiling @file{alloca.c}.
+
+Source files that use @code{alloca} should start with a piece of code
+like the following, to declare it properly. Note that in some versions
+of AIX, the declaration of @code{alloca} must precede everything else
+except for comments and preprocessor directives. The @code{#pragma}
+directive is indented so that pre-ANSI C compilers will ignore it,
+rather than choke on it.
+
+@example
+@group
+/* AIX requires this to be the first thing in the file. */
+#ifdef __GNUC__
+#define alloca __builtin_alloca
+#else /* not __GNUC__ */
+#if HAVE_ALLOCA_H
+#include <alloca.h>
+#else /* not HAVE_ALLOCA_H */
+#ifdef _AIX
+ #pragma alloca
+#else /* not _AIX */
+char *alloca ();
+#endif /* not _AIX */
+#endif /* not HAVE_ALLOCA_H */
+#endif /* not __GNUC__ */
+@end group
+@end example
+@end defmac
+
+@defmac AC_GETLOADAVG
+@findex GETLOADAVG
+@vindex NLIST_STRUCT
+@vindex NLIST_NAME_UNION
+@vindex GETLODAVG_PRIVILEGED
+@vindex NEED_SETGID
+Check how to get the system load averages. If the system has the
+@code{getloadavg} function, this macro defines @code{HAVE_GETLOADAVG},
+and adds to @code{LIBS} any libraries needed to get that function.
+
+Otherwise, it adds @samp{getloadavg.o} to the @code{make} variable
+@code{LIBOBJS}, and possibly defines several other C preprocessor
+macros and @code{make} variables:
+
+@enumerate
+@item
+It defines @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if
+on those systems.
+
+@item
+If it finds @file{nlist.h}, it defines @code{NLIST_STRUCT}.
+
+@item
+If @samp{struct nlist} has an @samp{n_un} member, it defines
+@code{NLIST_NAME_UNION}.
+
+@item
+If compiling @file{getloadavg.c} defines @code{LDAV_PRIVILEGED},
+programs need to be installed specially on this system for
+@code{getloadavg} to work, and this macro defines
+@code{GETLOADAVG_PRIVILEGED}.
+
+@item
+This macro always defines @code{NEED_SETGID}, for @code{make}. The
+value is @samp{true} if special installation is required, @samp{false}
+if not. If @code{NEED_SETGID} is @samp{true}, it sets @code{KMEM_GROUP}
+to the name of the group that should own the installed program.
+@end enumerate
+@end defmac
+
+@defmac AC_SETVBUF_REVERSED
+@findex SETVBUF_REVERSED
+@vindex SETVBUF_REVERSED
+If @code{setvbuf} takes the buffering type as its second argument and
+the buffer pointer as the third, instead of the other way around, define
+@code{SETVBUF_REVERSED}. This is the case on System V before release 3.
+@end defmac
+
+@defmac AC_STRCOLL
+@findex STRCOLL
+@vindex HAVE_STRCOLL
+Check for a proper declaration of the @code{strcoll} function. This
+does a bit more than @samp{AC_HAVE_FUNCS(strcoll)}, because some systems
+have incorrect definitions of @code{strcoll}, which should not be used.
+@end defmac
+
+@defmac AC_UTIME_NULL
+@findex UTIME_NULL
+@vindex HAVE_UTIME_NULL
+If @samp{utime(@var{file}, NULL)} sets @var{file}'s timestamp to
+the present, define @code{HAVE_UTIME_NULL}.
+@end defmac
+
+@defmac AC_VFORK
+@findex VFORK
+@vindex HAVE_VFORK_H
+@vindex vfork
+If @file{vfork.h} is found, define @code{HAVE_VFORK_H}. If a working
+@code{vfork} is not found, define @code{vfork} to be @code{fork}. This
+macro checks for several known errors in implementations of @code{vfork}
+and considers the system to not have a working @code{vfork} if it
+detects any of them.
+@end defmac
+
+@defmac AC_VPRINTF
+@findex VPRINTF
+@vindex HAVE_VPRINTF
+@vindex HAVE_DOPRNT
+If @code{vprintf} is found, define @code{HAVE_VPRINTF}. Otherwise, if
+@code{_doprnt} is found, define @code{HAVE_DOPRNT}.
+@end defmac
+
+@defmac AC_WAIT3
+@findex WAIT3
+@vindex HAVE_WAIT3
+If @code{wait3} is found and fills in the contents of its third argument
+(a @samp{struct rusage *}), which HP-UX does not do, define
+@code{HAVE_WAIT3}.
+@end defmac
+
+@node Structures, Compiler Characteristics, Library Functions, Specific Tests
+@section Structures
+
+The following macros check for certain structures or structure members:
+
+@defmac AC_STAT_MACROS_BROKEN
+@findex STAT_MACROS_BROKEN
+@findex STAT_MACROS_BROKEN
+If the macros @code{S_ISDIR}, @code{S_ISREG} et al. defined
+@file{sys/stat.h} do not work properly (returning false positives),
+define @code{STAT_MACROS_BROKEN}. This is the case on Tektronix UTekV,
+Amdahl UTS and Motorola System V/88.
+@end defmac
+
+@defmac AC_ST_BLKSIZE
+@findex ST_BLKSIZE
+@vindex HAVE_ST_BLKSIZE
+If @code{struct stat} contains an @code{st_blksize} member, define
+@code{HAVE_ST_BLKSIZE}.
+@end defmac
+
+@defmac AC_ST_BLOCKS
+@findex ST_BLOCKS
+@vindex HAVE_ST_BLOCKS
+If @code{struct stat} contains an @code{st_blocks} member, define
+@code{HAVE_ST_BLOCKS}. Otherwise, add @samp{fileblocks.o} to the
+@code{make} variable @code{LIBOBJS}.
+@end defmac
+
+@defmac AC_ST_RDEV
+@findex ST_RDEV
+@vindex HAVE_ST_RDEV
+If @code{struct stat} contains an @code{st_rdev} member, define
+@code{HAVE_ST_RDEV}.
+@end defmac
+
+@defmac AC_TIME_WITH_SYS_TIME
+@findex TIME_WITH_SYS_TIME
+@vindex TIME_WITH_SYS_TIME
+If a program may include both @file{time.h} and @file{sys/time.h},
+define @code{TIME_WITH_SYS_TIME}. On some older systems,
+@file{sys/time.h} includes @file{time.h}, but @file{time.h} is not
+protected against multiple inclusion, so programs should not explicitly
+include both files. This macro is useful in programs that use, for
+example, @code{struct timeval} or @code{struct timezone} as well as
+@code{struct tm}. It is best used in conjunction with
+@code{HAVE_SYS_TIME_H}.
+
+@example
+#ifdef TIME_WITH_SYS_TIME
+#include <sys/time.h>
+#include <time.h>
+#else
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#else
+#include <time.h>
+#endif
+#endif
+@end example
+@end defmac
+
+@defmac AC_STRUCT_TM
+@findex STRUCT_TM
+@vindex TM_IN_SYS_TIME
+If @file{time.h} does not define @code{struct tm}, define
+@code{TM_IN_SYS_TIME}, which means that including @file{sys/time.h}
+defines @code{struct tm}.
+@end defmac
+
+@defmac AC_TIMEZONE
+@findex TIMEZONE
+@vindex HAVE_TM_ZONE
+@vindex HAVE_TZNAME
+Figure out how to get the current timezone. If @code{struct tm} has a
+@code{tm_zone} member, define @code{HAVE_TM_ZONE}. Otherwise, if the
+external array @code{tzname} is found, define @code{HAVE_TZNAME}. This
+macro calls @code{AC_STRUCT_TM} if it hasn't been called already.
+@end defmac
+
+@node Compiler Characteristics, System Services, Structures, Specific Tests
+@section Compiler Characteristics
+
+The following macros check for C compiler or machine architecture
+features:
+
+@defmac AC_ARG_ARRAY
+@findex ARG_ARRAY
+@vindex NO_ARG_ARRAY
+If the address of an argument to a C function can not be used like
+the start of an array, define @code{NO_ARG_ARRAY}. This ability allows
+a sequence of arguments with the same type to be accessed as if they
+were an array of values.
+@end defmac
+
+@defmac AC_CROSS_CHECK
+@findex CROSS_CHECK
+If the C compiler being used does not produce executables that can run
+on the system where @code{configure} is being run, set the shell
+variable @code{cross_compiling} to 1. This information can be used by
+@code{AC_TEST_PROGRAM} to determine whether to take a default action
+instead of trying to run a test program (@pxref{General Tests}).
+@end defmac
+
+@defmac AC_CHAR_UNSIGNED
+@findex CHAR_UNSIGNED
+@vindex __CHAR_UNSIGNED__
+If the C type @code{char} is unsigned, define @code{__CHAR_UNSIGNED__},
+unless the C compiler predefines it.
+@end defmac
+
+@defmac AC_CONST
+@findex CONST
+@vindex const
+If the C compiler does not fully support the keyword @code{const},
+define @code{const} to be empty. Some C compilers that do not define
+@code{__STDC__} do support @code{const}; some compilers that define
+@code{__STDC__} do not completely support @code{const}. Programs can
+simply use @code{const} as if every C compiler supported it; for those
+that don't, the @file{Makefile} or configuration header file will define
+it as empty. (If using a configuration header file, the program should
+include it before any other header files, to prevent inconsistencies in
+declarations.)
+@end defmac
+
+@defmac AC_INLINE
+@findex INLINE
+@vindex inline
+If the C compiler is a version of GCC that supports the keyword
+@code{__inline} but not @code{inline} (such as some NeXT versions),
+define @code{inline} to be @code{__inline}. This macro calls
+@code{AC_PROG_CC} if it hasn't been called already.
+@end defmac
+
+@defmac AC_INT_16_BITS
+@findex INT_16_BITS
+@vindex INT_16_BITS
+If the C type @code{int} is smaller than the type @code{long}, define
+@code{INT_16_BITS}.
+@end defmac
+
+@defmac AC_LONG_DOUBLE
+@findex HAVE_LONG_DOUBLE
+@vindex HAVE_LONG_DOUBLE
+If the C compiler supports the @code{long double} type, define
+@code{HAVE_LONG_DOUBLE}. Some C compilers that do not define
+@code{__STDC__} do support the @code{long double} type; some compilers
+that define @code{__STDC__} do not support @code{long double}.
+@end defmac
+
+@defmac AC_WORDS_BIGENDIAN
+@findex WORDS_BIGENDIAN
+@vindex WORDS_BIGENDIAN
+If words are stored with the most significant byte first (like Motorola
+and SPARC, but not Intel and VAX, CPUs), define @code{WORDS_BIGENDIAN}.
+@end defmac
+
+@node System Services, UNIX Variants, Compiler Characteristics, Specific Tests
+@section System Services
+
+The following macros check for operating system services:
+
+@defmac AC_FIND_X
+@findex FIND_X
+Try to locate the X Window System include files and libraries by running
+@code{xmkmf} on a trivial @file{Imakefile} and examining the
+@file{Makefile} that it produces. If successful, set the shell
+variables @code{x_includes} and @code{x_libraries} to their locations;
+otherwise (such as if @code{xmkmf} is not present), do nothing.
+@end defmac
+
+@defmac AC_HAVE_POUNDBANG (@var{action-if-supported} @r{[}, @var{action-if-unsupported}@r{]})
+@findex HAVE_POUNDBANG
+Print @samp{checking if `#!' works in shell scripts} to the standard
+output. Then check whether the system supports starting shell scripts
+with a line of the form @samp{#!/bin/csh} to select the shell to run
+them with. @var{action-if-supported} is a list of shell commands to run
+if @samp{#!} works; @var{action-if-not-supported} is a list of shell
+commands to run otherwise.
+@end defmac
+
+@defmac AC_LONG_FILE_NAMES
+@findex LONG_FILE_NAMES
+@vindex HAVE_LONG_FILE_NAMES
+If the system supports file names longer than 14 characters, define
+@code{HAVE_LONG_FILE_NAMES}.
+@end defmac
+
+@defmac AC_REMOTE_TAPE
+@findex REMOTE_TAPE
+@vindex HAVE_SYS_MTIO_H
+If BSD tape drive ioctls are available, define @code{HAVE_SYS_MTIO_H},
+and if sockets are available add @code{rmt} to @code{make} variable
+@code{PROGS}.
+@end defmac
+
+@defmac AC_RESTARTABLE_SYSCALLS
+@findex RESTARTABLE_SYSCALLS
+@vindex HAVE_RESTARTABLE_SYSCALLS
+If the system automatically restarts a system call that is interrupted
+by a signal, define @code{HAVE_RESTARTABLE_SYSCALLS}.
+@end defmac
+
+@node UNIX Variants, , System Services, Specific Tests
+@section UNIX Variants
+
+The following macros check for certain operating systems that need
+special treatment for some programs, due to exceptional oddities in
+their header files or libraries:
+
+@defmac AC_AIX
+@findex AIX
+@vindex _ALL_SOURCE
+If on AIX, define @code{_ALL_SOURCE}. Allows the use of some BSD
+functions. Should be called before any macros that run the C compiler.
+@end defmac
+
+@defmac AC_DYNIX_SEQ
+@findex DYNIX_SEQ
+If on DYNIX/ptx (Sequent UNIX), add @samp{-lseq} to @code{make}
+variable @code{LIBS}. Allows use of some BSD system calls and
+@code{getmntent}.
+@end defmac
+
+@defmac AC_IRIX_SUN
+@findex IRIX_SUN
+If on IRIX (Silicon Graphics UNIX), add @samp{-lsun} to @code{make}
+variable @code{LIBS}. Needed to get @code{getmntent}. At sites using
+Yellow Pages/NIS, it is also needed to get properly working
+@code{gethostby*}, @code{getpw*}, @code{getgr*}, @code{getnetby*}, and
+so on.
+@c (According to Garrett.Wollman@uvm.edu.)
+@end defmac
+
+@defmac AC_ISC_POSIX
+@findex ISC_POSIX
+@vindex _POSIX_SOURCE
+If on a POSIXized ISC UNIX, define @code{_POSIX_SOURCE} and add
+@samp{-posix} (for the GNU C compiler) or @samp{-Xp} (for other C
+compilers) to @code{make} variable @code{CC}. This allows the use of
+POSIX facilities. Must be called after @code{AC_PROG_CC} and before
+any other macros that run the C compiler.
+@end defmac
+
+@defmac AC_MINIX
+@findex MINIX
+@vindex _MINIX
+@vindex _POSIX_SOURCE
+@vindex _POSIX_1_SOURCE
+If on Minix, define @code{_MINIX} and @code{_POSIX_SOURCE} and define
+@code{_POSIX_1_SOURCE} to be 2. This allows the use of POSIX
+facilities. Should be called before any macros that run the C compiler.
+@end defmac
+
+@defmac AC_SCO_INTL
+@findex SCO_INTL
+If on SCO UNIX, add @samp{-lintl} to @code{make} variable @code{LIBS}.
+Used to get @code{strftime}. It must be called before checking for
+@code{strftime}.
+@end defmac
+
+@defmac AC_XENIX_DIR
+@findex XENIX_DIR
+@vindex VOID_CLOSEDIR
+If on Xenix, define @code{VOID_CLOSEDIR} and add @samp{-lx} to
+@code{make} variable @code{LIBS}. Also, if @file{sys/ndir.h} is not
+being used, add @samp{-ldir} to @code{LIBS}. Needed when using the
+directory reading functions. This macro must be called after
+@code{AC_DIR_HEADER}.
+@end defmac
+
+@node General Purpose Macros, Writing Macros, Specific Tests, Top
+@chapter General Purpose Macros
+
+These macros provide ways for other macros to control the kind of output
+that Autoconf produces or to check whether various kinds of features are
+available. They all take arguments. When calling these macros, there
+must not be any blank space between the macro name and the open
+parentheses.
+
+Arguments to these macros can be more than one line long if they are
+enclosed within the @code{m4} quote characters @samp{[} and @samp{]}.
+
+Within each section below, the macros are listed in alphabetical order.
+These macros are defined in the file @file{acgeneral.m4}.
+
+@menu
+* Setup:: Controlling Autoconf operation.
+* General Tests:: Check for kinds of features.
+* Setting Variables:: Setting shell and @code{make} variables.
+* Macro Ordering:: Enforcing ordering constraints.
+@end menu
+
+@node Setup, General Tests, , General Purpose Macros
+@section Controlling Autoconf Setup
+
+The following macros control the kind of output that Autoconf produces.
+
+@defmac AC_CONFIG_HEADER (@var{header-to-create})
+@findex CONFIG_HEADER
+@vindex HAVE_CONFIG_H
+Make @code{AC_OUTPUT} create a file @var{header-to-create} containing C
+preprocessor @code{#define} statements and replace @samp{@@DEFS@@} in
+generated files with @samp{-DHAVE_CONFIG_H} instead of the value of
+@code{DEFS}. @xref{Setup}, for more information on @code{AC_OUTPUT}.
+This macro should be called right after @code{AC_INIT}. The usual name
+for @var{header-to-create} is @file{config.h}.
+
+If @var{header-to-create} already exists and its contents are identical
+to what @code{AC_OUTPUT} would put in it, it is left alone. Doing this
+allows some changes in configuration without needlessly causing object
+files that depend on the header file to be recompiled.
+
+Your distribution should contain a file @file{@var{header-to-create}.in}
+that looks as you want the final header file to look, including
+comments, with default values in the @code{#define} statements. A
+default value can be to @code{#undef} the variable instead of to define
+it to a value, if your code tests for configuration options using
+@code{#ifdef} instead of @code{#if}.
+
+You can use the program @code{autoheader} to create
+@file{@var{header-to-create}.in} (@pxref{Invoking autoheader}).
+@end defmac
+
+@defmac AC_INIT (@var{unique-file-in-source-dir})
+@findex INIT
+Process the command-line arguments and find the source code directory.
+@var{unique-file-in-source-dir} is some file that is in the package's
+source directory; @code{configure} checks for this file's existence to
+make sure that the directory that it is told contains the source code in
+fact does (@pxref{Running configure Scripts}, for more information).
+@end defmac
+
+@defmac AC_PREPARE (@var{unique-file-in-source-dir})
+@findex PREPARE
+Find the source code directory and set up shell variables necessary for
+other Autoconf macros to work. @var{unique-file-in-source-dir} is some
+file that is in the package's source directory; @code{configure} checks
+for this file's existence to make sure that the directory that it is
+told contains the source code in fact does (@pxref{Running configure
+Scripts}, for more information). @code{AC_PREPARE} is the last thing
+done by @code{AC_INIT}. Use @code{AC_PREPARE} instead of @code{AC_INIT}
+if you want to do argument parsing yourself; never use both.
+@end defmac
+
+@defmac AC_OUTPUT (@r{[}@var{file}@dots{}@r{]})
+@findex OUTPUT
+Create output files (typically one or more @file{Makefile}s) and
+@file{config.status}. If @code{AC_CONFIG_HEADER} has been called, also
+create the header file that was named as its argument. The argument is
+a whitespace-separated list of files to create; if it is omitted, no
+files are created. @code{AC_OUTPUT} creates each file @file{@var{file}}
+in the list by copying @file{@var{file}.in}, substituting the variable
+values that have been selected by calling @code{AC_SUBST}. It creates
+the directory that each file is in if it doesn't exist (but not the
+parents of that directory). A plausible value for the argument to
+@code{AC_OUTPUT} is @samp{Makefile src/Makefile man/Makefile
+X/Imakefile}.
+@end defmac
+
+@defmac AC_REVISION (@var{revision-info})
+@findex REVISION
+Copy revision stamp @var{revision-info} into the @file{configure}
+script, with any dollar signs or double-quotes removed. This macro lets
+you put a revision stamp from @file{configure.in} into @file{configure}
+without RCS or CVS changing it when you check in @file{configure}. That
+way, you can determine easily which revision of @file{configure.in} a
+particular @file{configure} corresponds to.
+
+It is a good idea to call this macro before @code{AC_INIT} so that the
+revision number is near the top of both @file{configure.in} and
+@file{configure}. To support doing that, the @code{AC_REVISION} output
+begins with @samp{#!/bin/sh}, like the normal start of a
+@file{configure} script does.
+
+For example, this line in @file{configure.in}:
+
+@example
+ifdef([AC_REVISION],AC_REVISION($Revision$),)dnl
+@end example
+
+@noindent
+produces this in @file{configure}:
+
+@example
+#!/bin/sh
+# From configure.in Revision: 1.30
+@end example
+@end defmac
+
+@node General Tests, Setting Variables, Setup, General Purpose Macros
+@section Checking for Kinds of Features
+
+These macros are templates that, when called with actual parameters,
+check for various kinds of features. Many of these macros handle two
+cases: what to do if the given condition is met, and what to do if the
+condition is not met. In some places you you might want to do something
+if a condition is true but do nothing if it's false, or vice versa. To
+omit the true case, pass an empty value for the @var{action-if-found}
+argument to the macro. To omit the false case, omit the
+@var{action-if-not-found} argument to the macro, including the comma
+before it.
+
+One shell programming construction that you should not use in the action
+arguments to these macros is @samp{@var{var}=$@{@var{var}:-@var{value}@}}.
+Old BSD shells, including the Ultrix @code{sh}, don't understand the
+colon, and complain and die. If you omit the colon, it works fine:
+@samp{@var{var}=$@{@var{var}-@var{value}@}}.
+
+@xref{Writing Macros}, for more information on how best to use these
+macros.
+
+@defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex COMPILE_CHECK
+Print @samp{checking for @var{echo-text}} to the standard output. Then
+create a test C program to see whether a function whose body consists of
+@var{function-body} can be compiled and linked; @var{includes} is any
+@code{#include} statements needed by the code in @var{function-body}.
+If the file compiles and links successfully, run shell commands
+@var{action-if-found}, otherwise run @var{action-if-not-found}.
+@end defmac
+
+@defmac AC_FUNC_CHECK (@var{function}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex FUNC_CHECK
+If @var{function} is available, run shell commands
+@var{action-if-found}, otherwise @var{action-if-not-found}. If the
+functions might be in libraries other than the default C library, first
+call @code{AC_HAVE_LIBRARY} for those libraries. If you just want to
+define a symbol if the function is available, consider using
+@code{AC_HAVE_FUNCS} instead.
+@end defmac
+
+@defmac AC_HAVE_FUNCS (@var{function}@dots{})
+@findex HAVE_FUNCS
+@vindex HAVE_@var{function}
+For each given @var{function} in the whitespace-separated argument list
+that is available, define @code{HAVE_@var{function}} (in all caps).
+@xref{Specific Tests}, for a precise definition of ``define'' as it
+is used here. If the functions might be in libraries other than the
+default C library, first call @code{AC_HAVE_LIBRARY} for those libraries.
+@end defmac
+
+@defmac AC_HAVE_HEADERS (@var{header-file}@dots{})
+@findex HAVE_HEADERS
+@vindex HAVE_@var{header}
+For each given @var{header-file} in the whitespace-separated argument
+list that exists, define @code{HAVE_@var{header-file}} (in all caps).
+@xref{Specific Tests}, for a precise definition of ``define'' as
+it is used here.
+@end defmac
+
+@defmac AC_HAVE_LIBRARY (@var{library} @r{[}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]]})
+@findex HAVE_LIBRARY
+Print @samp{checking for @var{library}} to the standard output. Then
+create a test C program to see whether that program can be linked with
+the specified library. @var{action-if-found} is a list of shell
+commands to run if the link succeeds (which means that the library is
+present); @var{action-if-not-found} is a list of shell commands to run
+if the link fails. If @var{action-if-found} and
+@var{action-if-not-found} are not specified, the default action is to
+add @samp{-lfoo} to @code{LIBS} and define @samp{HAVE_LIBfoo}
+for library @samp{foo}. @var{library} can be written as any of
+@samp{foo}, @samp{-lfoo}, or @samp{libfoo.a}. In all of those cases,
+the compiler is passed @samp{-lfoo}.
+@end defmac
+
+@defmac AC_HEADER_CHECK (@var{header-file}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex HEADER_CHECK
+If @var{header-file} exists, execute shell commands
+@var{action-if-found}, otherwise execute @var{action-if-not-found}. If
+you just want to define a symbol if the header file is available,
+consider using @code{AC_HAVE_HEADERS} instead.
+@end defmac
+
+@defmac AC_HEADER_EGREP (@var{pattern}, @var{header-file}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex HEADER_EGREP
+If the output of running the C preprocessor on @var{header-file}
+contains the @code{egrep} regular expression @var{pattern}, execute
+shell commands @var{action-if-found}, otherwise execute
+@var{action-if-not-found}.
+
+You can not check whether preprocessor symbols are defined this way,
+because they get expanded before @code{egrep} sees them. You can
+probably just put @code{#ifdef} directives in your C programs to detect
+them, but if you want to do the check in @code{configure} for some
+reason (perhaps to determine which of several files to include), then
+use @code{AC_PROGRAM_EGREP}, like this:
+
+@example
+AC_PROGRAM_EGREP(yes, [#include <stdio.h>
+#ifdef P_tmpdir
+yes
+#endif
+], AC_DEFINE(HAVE_P_TMPDIR))
+@end example
+@end defmac
+
+@defmac AC_PREFIX (@var{program})
+@findex PREFIX
+If the user did not specify an installation prefix on the command line,
+guess a value for it by looking for @var{program} in @code{PATH}, the
+way the shell does. If @var{program} is found, set the prefix to the
+parent of the directory containing @var{program}; otherwise leave the
+prefix specified in @file{Makefile.in} unchanged. For example, if
+@var{program} is @code{gcc} and the @code{PATH} contains
+@file{/usr/local/gnu/bin/gcc}, set the prefix to @file{/usr/local/gnu}.
+@end defmac
+
+@defmac AC_PROGRAM_CHECK (@var{variable}, @var{prog-to-check-for}, @var{value-if-found}, @var{value-if-not-found})
+@findex PROGRAM_CHECK
+Check whether program @var{prog-to-check-for} exists in @code{PATH}. If
+it is found, set @var{variable} to @var{value-if-found}, otherwise to
+@var{value-if-not-found}. Calls @code{AC_SUBST} for @var{variable}.
+@end defmac
+
+@defmac AC_PROGRAM_EGREP (@var{pattern}, @var{program}, @var{action-if-found} @r{[}, @var{action-if-not-found}@r{]})
+@findex PROGRAM_EGREP
+@var{program} is the text of a C program, on which shell variable and
+backquote substitutions are performed. If the output of running the C
+preprocessor on @var{program} contains the @code{egrep} regular
+expression @var{pattern}, execute shell commands @var{action-if-found},
+otherwise execute @var{action-if-not-found}. (It is an unfortunate
+oversight that we use the word ``PROGRAM'' in Autoconf macro names to
+sometimes mean C source code and sometimes mean a UNIX command.)
+@end defmac
+
+@defmac AC_PROGRAMS_CHECK (@var{variable}, @var{progs-to-check-for} @r{[}, @var{value-if-not-found}@r{]})
+@findex PROGRAMS_CHECK
+Check for each program in the whitespace-separated list
+@var{progs-to-check-for} exists in @code{PATH}. If it is found, set
+@var{variable} to the name of that program. Otherwise, continue
+checking the next program in the list. If none of the programs in the
+list are found, set @var{variable} to @var{value-if-not-found}; if
+@var{value-if-not-found} is not specified, the value of @var{variable}
+will not be changed. Calls @code{AC_SUBST} for @var{variable}.
+@end defmac
+
+@defmac AC_REPLACE_FUNCS (@var{function-name}@dots{})
+@findex REPLACE_FUNCS
+For each given @var{function-name} in the whitespace-separated argument
+list that is not in the C library, add @samp{@var{function-name}.o} to
+the value of the @code{make} variable @code{LIBOBJS}. If the functions
+might be in libraries other than the default C library, first call
+@code{AC_HAVE_LIBRARY} for those libraries.
+@end defmac
+
+@defmac AC_TEST_PROGRAM (@var{program}, @var{action-if-true} @r{[}, @var{action-if-false} @r{[}, @var{action-if-cross-compiling}@r{]]})
+@findex TEST_PROGRAM
+@var{program} is the text of a C program, on which shell variable and
+backquote substitutions are performed. If it compiles and links
+successfully and returns an exit status of 0 when executed, run shell
+commands @var{action-if-true}. Otherwise run shell commands
+@var{action-if-false}.
+
+If the optional argument @var{action-if-cross-compiling} is given and
+the C compiler being used does not produce executables that run on the
+system where @code{configure} is being run, then the test program is not
+run. Instead, the shell commands @var{action-if-cross-compiling} are
+run. If that argument is given, this macro calls @code{AC_CROSS_CHECK}
+if it has not already been called (@pxref{Compiler Characteristics}).
+@end defmac
+
+@defmac AC_TEST_CPP (@var{includes}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]})
+@findex TEST_CPP
+@var{includes} is C @code{#include} statements and declarations, on
+which shell variable and backquote substitutions are performed.
+(Actually, it can be any C program, but other statements are probably
+not useful.) If the C preprocessor produces no error messages while
+processing it, run shell commands @var{action-if-true}. Otherwise run
+shell commands @var{action-if-false}.
+
+This macro calls @code{AC_PROG_CPP} if it hasn't been called already.
+@end defmac
+
+@defmac AC_WITH (@var{feature}, @var{action-if-true} @r{[}, @var{action-if-false}@r{]})
+@findex WITH
+If the user gave @code{configure} the option
+@samp{--with-@var{feature}}, run shell commands @var{action-if-true}.
+Otherwise run shell commands @var{action-if-false}. The name
+@var{feature} should consist only of alphanumeric characters and dashes;
+typical feature names are @samp{gnu-libc} and @samp{x}.
+
+The user can give a value by following the feature name with @samp{=}
+and the value; for example,
+
+@example
+./configure --with-targets=sun4,hp300bsd
+@end example
+
+The value given is available to the shell commands @var{action-if-true}
+in the shell variable @code{withval}. If no value was given,
+@code{withval} is 1. For example,
+
+@example
+AC_WITH(fubar, echo "got --with-fubar=$withval",
+ echo no --with-fubar)
+@end example
+@end defmac
+
+@node Setting Variables, Macro Ordering, General Tests, General Purpose Macros
+@section Setting Variables
+
+These macros help other macros to define shell and @code{make}
+variables.
+
+@defmac AC_DEFINE (@var{variable} @r{[}, @var{value}@r{]})
+@findex DEFINE
+Define C preprocessor variable @var{variable}. If @var{value} is given,
+set @var{variable} to that value, otherwise set it to 1. To use a shell
+variable as the value, use @code{AC_DEFINE_UNQUOTED} instead. Precede
+double quotes in the value with backslashes.
+
+This macro adds to the shell variable @code{DEFS}. @code{AC_OUTPUT}
+later substitutes the values in @code{DEFS} into the file(s) that it
+generates (typically @file{Makefile}). Alternately, if
+@code{AC_CONFIG_HEADER} has been called, @code{AC_OUTPUT} creates a
+header file by substituting the correct values into @code{#define}
+statements in a template file.
+
+For example, suppose your @file{configure.in} calls
+@code{AC_CONFIG_HEADER(conf.h)} and @code{AC_UNISTD_H}. You could have
+code like this in @file{conf.h.in}:
+
+@example
+@group
+/* Define as 1 if you have unistd.h. */
+#define HAVE_UNISTD_H 0
+@end group
+@end example
+
+On systems that have @file{unistd.h}, @code{configure} will change the 0
+to a 1. On other systems, it will leave the line unchanged.
+Alternately, if you prefer to use @code{#ifdef}, your @file{conf.h.in}
+could have code like this:
+
+@example
+@group
+/* Define if you have unistd.h. */
+#undef HAVE_UNISTD_H
+@end group
+@end example
+
+On systems that have @file{unistd.h}, @code{configure} will change the
+second line to read @samp{#define HAVE_UNISTD_H 1}. On other systems,
+it will leave the line unchanged.
+
+Due to the syntactical bizarreness of the Bourne shell, do not use
+semicolons to separate @code{AC_DEFINE} calls from other macro calls or
+shell code; that can cause syntax errors in the resulting
+@code{configure} script. Use either spaces or newlines. That is, do
+this:
+
+@example
+AC_HEADER_CHECK(elf.h, AC_DEFINE(SVR4) LIBS="$LIBS -lelf")
+@end example
+
+@noindent
+or this:
+
+@example
+AC_HEADER_CHECK(elf.h,
+ AC_DEFINE(SVR4)
+ LIBS="$LIBS -lelf")
+@end example
+
+@noindent
+instead of this:
+
+@example
+AC_HEADER_CHECK(elf.h, AC_DEFINE(SVR4); LIBS="$LIBS -lelf")
+@end example
+@end defmac
+
+@defmac AC_DEFINE_UNQUOTED (@var{variable} @r{[}, @var{value}@r{]})
+@findex DEFINE_UNQUOTED
+Like @code{AC_DEFINE}, but it does nothing to quote @var{value} from
+various shell and @code{sed} expansions it will undergo. @var{value}
+will be used in many different contexts requiring different quoting, and
+it is up to you to make sure it works right. Use this macro instead of
+@code{AC_DEFINE} when @var{value} contains a shell variable. For
+example:
+
+@example
+AC_DEFINE_UNQUOTED(config_machfile, $@{machfile@})
+@end example
+@end defmac
+
+@defmac AC_SUBST (@var{variable})
+@findex SUBST
+Substitute the variable @var{variable} when creating the output files
+(typically one or more @file{Makefile}s). This means replace instances
+of @samp{@@@var{variable}@@}, e.g. in @file{Makefile.in}, with the
+current value of the shell variable @var{variable}. If this macro were
+not called, the value of @var{variable} would not be set in the output
+files, even though @code{configure} had figured out a value for it.
+
+You can set or add to the value of @var{variable} in the usual shell
+way. For example, to add @samp{-ltermcap} to the value of the variable
+@code{LIBS}:
+
+@example
+LIBS="$LIBS -ltermcap"
+@end example
+@end defmac
+
+@node Macro Ordering, , Setting Variables, General Purpose Macros
+@section Macro Ordering
+
+These macros provide ways for other macros to make sure that they are
+called in the correct order.
+
+@defmac AC_BEFORE (@var{this-macro-name}, @var{called-macro-name})
+@findex BEFORE
+Make @code{m4} print a warning message on the standard error output if
+@var{called-macro-name} has already been called. @var{this-macro-name}
+should be the name of the macro that is calling @code{AC_BEFORE}. The
+macro @var{called-macro-name} must contain a call to @code{AC_PROVIDE}
+to indicate that it has been called.
+
+This macro should be used when one macro makes changes that might affect
+another macro, so that the other macro should probably not be called
+first. For example, @code{AC_PROG_CPP} checks whether the C compiler
+can run the C preprocessor when given the @samp{-E} option. It should
+therefore be called after any macros that change which C compiler is
+being used, such as @code{AC_PROG_CC}. So @code{AC_PROG_CC} contains:
+
+@example
+AC_BEFORE([$0], [AC_PROG_CPP])
+@end example
+
+@noindent
+This warns the user if a call to @code{AC_PROG_CPP} has already occurred
+when @code{AC_PROG_CC} is called.
+@end defmac
+
+@defmac AC_PROVIDE (@var{macro-name})
+@findex PROVIDE
+Set a flag recording that @var{macro-name} has been called. The
+argument should be the name of the macro that is calling
+@code{AC_PROVIDE}. An easy way to get it is from the @code{m4} builtin
+variable @code{$0}, like this:
+
+@example
+AC_PROVIDE([$0])
+@end example
+@end defmac
+
+@defmac AC_REQUIRE (@var{macro-name})
+@findex REQUIRE
+If the @code{m4} macro @var{macro-name} has not already been called,
+call it (without any arguments). Make sure to quote @var{macro-name}
+with square brackets. The body of @var{macro-name} must contain a call
+to @code{AC_PROVIDE} to indicate that it has been called.
+
+Macros that need some other macro to be called before they are called
+can use @code{AC_REQUIRE} to ensure that it has been, in case the person
+who made @file{configure.in} forgot or didn't know to do it.
+@code{AC_REQUIRE} and @code{AC_PROVIDE} together can ensure that a macro
+is only called if it is needed, and only called once.
+@xref{Dependencies Between Macros}, for more information.
+@end defmac
+
+@node Writing Macros, Makefiles, General Purpose Macros, Top
+@chapter Writing Macros
+
+If your package needs to test for some feature that none of the macros
+supplied with Autoconf handles, you'll need to write one or more new
+Autoconf macros. Here are some suggestions and some of the rationale
+behind why the existing macros are written the way they are. You can
+also learn a lot about how to write Autoconf macros by looking at the
+existing ones. If something goes wrong in one or more of the Autoconf
+tests, this information can help you understand why they work the way
+they do and the assumptions behind them, which might help you figure out
+how to best solve the problem.
+
+If you add macros that you think would be useful to other people, or
+find problems with the distributed macros, please send electronic mail
+to @file{bug-gnu-utils@@prep.ai.mit.edu}, so we can consider them for
+future releases of Autoconf. Please include the Autoconf version
+number, which you can get by running @samp{autoconf --version}.
+
+@menu
+* Macro Format:: Basic format of an Autoconf macro.
+* Quoting:: Protecting macros from unwanted expansion.
+* Dependencies Between Macros:: What to do when macros depend on other macros.
+* Checking for Files:: Finding whether a file exists.
+* Checking for Symbols:: Finding whether a symbol is defined.
+* Test Programs:: Writing programs to test for features.
+* Multiple Cases:: Tests for several possible values.
+@end menu
+
+@node Macro Format, Quoting, , Writing Macros
+@section Macro Format
+
+Autoconf macros are defined as arguments to the @code{m4} builtin
+command @code{define}. Their overall structure looks like this:
+
+@example
+define(@var{macro-name}, [@var{macro-body}])dnl
+@end example
+
+@noindent
+The square brackets here do not indicate optional text: they should
+literally be present in the macro definition.
+
+All of the Autoconf macros have names starting with @samp{AC_} to
+prevent them from accidentally conflicting with other text. You should
+prefix your own macro names with some other sequence, such as your
+initials or an abbreviation for the name of your organization or
+software package, to ensure that their names don't conflict with the
+names of present or future Autoconf macros.
+
+The @code{m4} builtin @code{dnl} prevents a newline from being inserted
+in the output where the macro is defined; without it, the generated
+@code{configure} script would begin with dozens of blank lines.
+@code{dnl} is also used to introduce comments in @code{m4}; it causes
+@code{m4} to discard the rest of the input line.
+
+You should quote the entire macro body with square brackets to avoid
+macro expansion problems (@pxref{Quoting}). You can refer to any
+arguments passed to the macro as @samp{$1}, @samp{$2}, etc.
+
+@xref{Definitions, , How to define new macros, m4.info, GNU m4}, for
+more complete information on writing @code{m4} macros.
+
+@node Quoting, Dependencies Between Macros, Macro Format, Writing Macros
+@section Quoting
+
+Macros that are called by other macros are evaluated by @code{m4}
+several times; each evaluation might require another layer of quotes to
+prevent unwanted expansions of macros or @code{m4} builtins, such as
+@samp{include} and @samp{$1}. Quotes are also required around macro
+arguments that contain commas, since commas separate the arguments from
+each other.
+
+Autoconf (in @file{acgeneral.m4}) changes the @code{m4} quote characters
+from the default @samp{`} and @samp{'} to @samp{[} and @samp{]}, because
+many of the macros use @samp{`} and @samp{'}, mismatched. However, in a
+few places the macros need to use brackets. In those places, they use
+the @code{m4} builtin command @code{changequote} to temporarily disable
+quoting before the code that uses brackets, like this:
+
+@example
+changequote(,)dnl
+@end example
+
+@noindent
+Then they turn quoting back on again with another call to
+@code{changequote}:
+
+@example
+changequote([,])dnl
+@end example
+
+When you create a @code{configure} script using newly written macros,
+examine it carefully to check whether you need to add more quotes in
+your macros. If one or more words have disappeared in the @code{m4}
+output, you need more quotes. When in doubt, quote.
+
+However, it's also possible to put on too many layers of quotes. If
+this happens, the resulting @code{configure} script will contain
+unexpanded macros. The @code{autoconf} program checks for this problem
+by doing @samp{grep AC_ configure}.
+
+@node Dependencies Between Macros, Checking for Files, Quoting, Writing Macros
+@section Dependencies Between Macros
+
+Some Autoconf macros depend on other macros having been called first in
+order to work correctly. Autoconf provides a way to ensure that certain
+macros are called if needed and a way to warn the user if macros are
+called in an order that might cause incorrect operation.
+
+@menu
+* Prerequisite Macros:: Ensuring required information.
+* Suggested Ordering:: Warning about possible ordering problems.
+@end menu
+
+@node Prerequisite Macros, Suggested Ordering, , Dependencies Between Macros
+@subsection Prerequisite Macros
+
+A macro that you write might need to use values that have previously
+been computed by other macros. For example, if you write a new macro
+that uses the C preprocessor, it depends on @code{AC_PROG_CPP} having
+been called first to set the shell variable @code{CPP}
+(@pxref{Alternative Programs}).
+
+Rather than forcing the user of the macros to keep track of all of the
+dependencies between them, you can use the macros @code{AC_PROVIDE} and
+@code{AC_REQUIRE} to do it automatically. @xref{Macro Ordering}, for more
+information on their syntax.
+
+The new macro that runs the C preprocessor should contain, somewhere
+before @code{CPP} is used, the statement
+
+@example
+AC_REQUIRE([AC_PROG_CPP])
+@end example
+
+@noindent
+and the macro @code{AC_PROG_CPP} should contain the statement (anywhere
+in its body)
+
+@example
+AC_PROVIDE([$0])
+@end example
+
+@noindent
+Then, when the new macro is run, it will invoke @code{AC_PROG_CPP} if
+and only if @code{AC_PROG_CPP} has not already been run.
+
+@node Suggested Ordering, , Prerequisite Macros, Dependencies Between Macros
+@subsection Suggested Ordering
+
+Some macros should be run before another macro if both are called, but
+neither requires the other to be called. For example, a macro like
+@code{AC_AIX} that changes the behavior of the C compiler (@pxref{UNIX
+Variants}) should be called before any macros that run the C compiler.
+Many of these dependencies are noted in the documentation.
+
+Autoconf provides a way to warn users when macros with this kind of
+dependency appear out of order in a @file{configure.in} file. The
+warning occurs when creating @file{configure} from @file{configure.in},
+not when running @file{configure}. It is not a fatal error;
+@file{configure} is created as usual.
+
+The @code{AC_BEFORE} macro causes @code{m4} to print a warning message
+on the standard error output when a macro is used before another macro
+which might change its behavior. The macro which should come first
+should contain a call to @code{AC_BEFORE} and the macro which should
+come later should contain a call to @code{AC_PROVIDE}.
+
+For example, @code{AC_AIX} contains
+
+@example
+AC_BEFORE([$0], [AC_COMPILE_CHECK])
+@end example
+
+@noindent
+and @code{AC_COMPILE_CHECK} contains
+
+@example
+AC_PROVIDE([$0])
+@end example
+
+@noindent
+As a result, if @code{AC_AIX} is called after @code{AC_COMPILE_CHECK},
+it will note that @code{AC_COMPILE_CHECK} has already been called and
+print a warning message.
+
+@node Checking for Files, Checking for Symbols, Dependencies Between Macros, Writing Macros
+@section Checking for Files
+
+If you need to check whether a file other than a C header file exists,
+use @samp{test -f @var{filename}}. If you need to make multiple checks
+using @code{test}, combine them with the shell operators @samp{&&} and
+@samp{||} instead of using the @code{test} operators @samp{-a} and
+@samp{-o}. On System V, the precedence of @samp{-a} and @samp{-o} is
+wrong relative to the unary operators; consequently, POSIX does not
+specify them, so using them is nonportable. If you combine @samp{&&}
+and @samp{||} in the same statement, keep in mind that they have equal
+precedence.
+
+Do not use @samp{test -x}, because 4.3BSD does not have it. Use
+@samp{test -f} or @samp{test -r} instead.
+
+@node Checking for Symbols, Test Programs, Checking for Files, Writing Macros
+@section Checking for Symbols
+
+If you need to check whether a symbol is defined in a C header file, you
+can use @code{AC_HEADER_EGREP} if the symbol is not a C preprocessor
+macro (@pxref{General Tests}), or compile a small test program that includes
+the file and references the symbol (@pxref{Test Programs}). Don't
+directly @code{grep} for the symbol in the file, because on some systems
+it might be defined in another header file that the file you are
+checking @samp{#include}s.
+
+However, if you need to check for a particular UNIX variant which is
+distinguished by having certain text in a certain file, then use
+@code{grep} (or @code{egrep}). But don't use @samp{grep -s} to suppress
+output, because @samp{grep -s} on System V does not suppress output,
+only error messages. Instead, redirect the standard output and standard
+error (in case the file doesn't exist) of @code{grep} to
+@file{/dev/null}. Check the exit status of @code{grep} to determine
+whether it found a match.
+
+To check whether the Autoconf macros have already defined a certain C
+preprocessor symbol, you can use a @code{case} statement like this:
+
+@example
+case "$DEFS" in
+ *HAVE_FOO*) ;;
+ *) LIBOBJS="$LIBOBJS foo.o" ;;
+esac
+@end example
+
+@noindent
+Make sure to enclose the variable name you are checking (usually
+@code{DEFS}) in double quotes, because otherwise some old versions of
+@code{bash} misinterpret the statement.
+
+@node Test Programs, Multiple Cases, Checking for Symbols, Writing Macros
+@section Test Programs
+
+Autoconf checks for many features by compiling small test programs. To
+find out whether a library function is available, Autoconf tries to
+compile a small program that uses it. This is unlike Larry Wall's
+Metaconfig, which uses @code{nm} or @code{ar} on the C library to try to
+figure out which functions are available. Trying to link with the
+function is usually a more reliable and flexible approach because it
+avoids dealing with the variations in the options and output formats of
+@code{nm} and @code{ar} and in the location of the standard libraries.
+It also allows @code{configure} to check aspects of the function's
+runtime behavior if needed. On the other hand, it is sometimes slower
+than scanning the libraries.
+
+If you need to check for a condition other than whether some symbol
+exists on the system or has a certain value, then you can't use
+@code{AC_COMPILE_CHECK} (@pxref{General Tests}). You have to write a
+test program by hand. You can compile and run it using
+@code{AC_TEST_PROGRAM} (@pxref{General Tests}).
+
+Try to avoid writing test programs if possible, because using them
+prevents people from configuring your package for cross-compiling. If
+it's really best that you test for a run-time behavior, try to provide a
+default ``worst case'' value to use when cross-compiling makes run-time
+tests impossible. You do this by passing the optional last argument to
+@code{AC_TEST_PROGRAM}.
+
+@menu
+* Guidelines:: General rules for writing test programs.
+* Tricks:: Special ways to work around problems.
+@end menu
+
+@node Guidelines, Tricks, , Test Programs
+@subsection Guidelines for Test Programs
+
+Test programs should return 0 if the test succeeds, nonzero otherwise,
+so that success can be distinguished easily from a core dump or other
+failure; segmentation violations and other failures produce a nonzero
+exit status. Test programs should @code{exit}, not @code{return}, from
+@code{main}, because on some systems the argument to @code{return} in
+@code{main} is ignored. They should not write anything to the standard
+output.
+
+Test programs can use @code{#if} or @code{#ifdef} to check the values of
+preprocessor macros defined by tests that have already run. For
+example, if you call @code{AC_STDC_HEADERS}, then later on in
+@file{configure.in} you can have a test program that includes an ANSI C
+header file conditionally:
+
+@example
+@group
+#if STDC_HEADERS
+#include <stdlib.h>
+#endif
+@end group
+@end example
+
+If a test program needs to use or create a data file, give it a name
+that starts with @file{conftest}, such as @file{conftestdata}. The
+@code{configure} script cleans up by running @samp{rm -rf conftest*}
+after running test programs and if the script is interrupted.
+
+@node Tricks, , Guidelines, Test Programs
+@subsection Tricks for Test Programs
+
+If a test program calls a function with invalid parameters (just to see
+whether it exists), organize the program to ensure that it never invokes
+that function. You can do this by calling it in another function that is
+never invoked. You can't do it by putting it after a call to
+@code{exit}, because GCC version 2 knows that @code{exit} never returns
+and optimizes out any code that follows it in the same block.
+
+If you include any header files, make sure to call the functions
+relevant to them with the correct number of arguments, even if they are
+just 0, to avoid compilation errors due to prototypes. GCC version 2
+has internal prototypes for several functions that it automatically
+inlines; for example, @code{memcpy}. To avoid errors when checking for
+them, either pass them the correct number of arguments or redeclare them
+with a different return type (such as @code{char}).
+
+@node Multiple Cases, , Test Programs, Writing Macros
+@section Multiple Cases
+
+Some operations are accomplished in several possible ways, depending on
+the UNIX variant. Checking for them essentially requires a ``case
+statement''. Autoconf does not directly provide one; however, it is
+easy to simulate by using a shell variable to keep track of whether a
+way to perform the operation has been found yet.
+
+Here is an example excerpted from the @file{configure.in} for GNU
+@code{find}. It uses the shell variable @code{fstype} to keep track of
+whether the remaining cases need to be checked. There are several more
+cases which are not shown here but follow the same pattern.
+
+@example
+@group
+echo checking how to get filesystem type
+# SVR4.
+AC_TEST_CPP([#include <sys/statvfs.h>
+#include <sys/fstyp.h>], AC_DEFINE(FSTYPE_STATVFS) fstype=1)
+if test -z "$fstype"; then
+# SVR3.
+AC_TEST_CPP([#include <sys/statfs.h>
+#include <sys/fstyp.h>], AC_DEFINE(FSTYPE_USG_STATFS) fstype=1)
+fi
+if test -z "$fstype"; then
+# AIX.
+AC_TEST_CPP([#include <sys/statfs.h>
+#include <sys/vmount.h>], AC_DEFINE(FSTYPE_AIX_STATFS) fstype=1)
+fi
+@end group
+@end example
+
+@node Makefiles, Running configure Scripts, Writing Macros, Top
+@chapter Makefiles
+
+Each subdirectory in a distribution should come with a file
+@file{Makefile.in}, from which @code{configure} will produce a
+@file{Makefile} in that directory. Most of the substitutions that
+@code{configure} does are simple: for each configuration variable that
+the package uses, it just replaces occurrences of
+@samp{@@@var{variable}@@} with the value that @code{configure} has
+determined for that variable. Any occurrences of
+@samp{@@@var{variable}@@} for variables that @code{configure} does not
+know about are passed through unchanged.
+
+There is no point in checking for the correct value to give a variable
+that is never used. Every variable that the @code{configure} script
+might set a value for should appear in a @samp{@@@var{variable}@@} reference
+in at least one @file{Makefile.in}. If @code{AC_CONFIG_HEADER} is
+called, @code{configure} replaces @samp{@@DEFS@@} with
+@samp{-DHAVE_CONFIG_H}, since the contents of @code{DEFS} would be
+redundant.
+
+@xref{Makefiles, , Makefile Conventions, standards.info, The GNU Coding
+Standards}, for more information on what to put in Makefiles.
+@xref{Sample Makefile.in}, for an example of a real @file{Makefile.in}.
+
+@menu
+* Predefined Variables:: Heavily used @code{make} variables.
+* Installation Prefixes:: A special variable substitution.
+* VPATH Substitutions:: Compiling in a different directory.
+* Automatic Remaking:: Makefile rules for configuring.
+@end menu
+
+@node Predefined Variables, Installation Prefixes, , Makefiles
+@section Predefined Variables
+
+Some @code{make} variables are predefined by the Autoconf macros.
+@code{AC_SUBST} is called for them automatically (@pxref{Setting
+Variables}), so in your @file{Makefile.in} files you can get their
+values by enclosing their names in @samp{@@} characters
+(@pxref{Makefiles}). The variables that are defined by the general
+purpose Autoconf macros are:
+
+@defvar srcdir
+The directory that contains the source code for that @file{Makefile}.
+@end defvar
+
+@defvar DEFS
+@samp{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADER}
+is called, @code{configure} replaces @samp{@@DEFS@@} with
+@samp{-DHAVE_CONFIG_H}, since the contents of @code{DEFS} would be
+redundant.
+@end defvar
+
+@defvar LIBS
+@samp{-l} and @samp{-L} options to pass to the linker.
+@end defvar
+
+@defvar LIBOBJS
+Names of object files (ending in @file{.o}). Set by
+@code{AC_REPLACE_FUNCS} (@pxref{General Tests}).
+@end defvar
+
+@node Installation Prefixes, VPATH Substitutions, Predefined Variables, Makefiles
+@section Installation Prefixes
+
+If @code{configure} has figured out a value for the installation prefix,
+either by the user supplying one on the command line (@pxref{Running
+configure Scripts}) or with @code{AC_PREFIX}, then it substitutes that
+value in @file{Makefile}s that it creates. Wherever a @file{Makefile.in}
+contains a line like
+
+@example
+prefix = /usr/local
+@end example
+
+@noindent
+@code{configure} substitutes the value it figured out. The word
+@samp{prefix} must not be preceded by any other characters on the line.
+If @code{configure} has not figured out a value for the prefix, the
+value in the @file{Makefile.in} is left alone.
+
+There can be separate installation prefixes for architecture-specific
+files and architecture-independent files @pxref{Running configure
+Scripts}). @code{configure} substitutes the word @code{exec_prefix} in
+the same way that it does @code{prefix}.
+
+Autoconf @code{configure} scripts replace these two variables without
+requiring them to be enclosed in @samp{@@} characters, and only if they
+have been set, because the Cygnus @code{configure} does so. In
+retrospect, being compatible in this way was a bad decision, because it
+created an inconsistency in Autoconf without giving significant
+benefits.
+
+@node VPATH Substitutions, Automatic Remaking, Installation Prefixes, Makefiles
+@section @code{VPATH} Substitutions
+
+You might want to compile a software package in a different directory
+from the one that contains the source code. Doing this allows you to
+compile the package for several architectures simultaneously from the
+same copy of the source code and keep multiple sets of object files on
+disk.
+
+To support doing this, @code{make} uses the @code{VPATH} variable to
+find the files that are in the source directory. GNU @code{make} and
+most other recent @code{make} programs can do this. Older @code{make}
+programs do not support @code{VPATH}; when using them, the source code
+must be in the same directory as the object files.
+
+To support @code{VPATH}, each @file{Makefile.in} should contain two
+lines that look like:
+
+@example
+srcdir = @@srcdir@@
+VPATH = @@srcdir@@
+@end example
+
+Do not set @code{VPATH} to the value of another variable, for example
+@samp{VPATH = $(srcdir)}, because some versions of @code{make} do not do
+variable substitutions on the value of @code{VPATH}.
+
+@code{configure} substitutes in the correct value for @code{srcdir} when
+it produces @file{Makefile.in}.
+
+Do not use the @code{make} variable @code{$<}, which expands to the
+pathname of the file in the source directory (found with @code{VPATH}),
+except in implicit rules. (An implicit rule is one such as @samp{.c.o},
+which tells how to create a @file{.o} file from a @file{.c} file.) Some
+versions of @code{make} do not set @code{$<} in explicit rules; they
+expand it to an empty value.
+
+Instead, @file{Makefile} command lines should always refer to source
+files by prefixing them with @samp{$(srcdir)/}. For example:
+
+@example
+time.info: time.texinfo
+ $(MAKEINFO) $(srcdir)/time.texinfo
+@end example
+
+@node Automatic Remaking, , VPATH Substitutions, Makefiles
+@section Automatic Remaking
+
+You can put rules like the following in the top-level @file{Makefile.in}
+for a package to automatically update the configuration information when
+you change the configuration files.
+
+@example
+# The next rule also takes care of making config.h from config.h.in.
+# If remaking config.h does not change it, its timestamp is untouched.
+Makefile: Makefile.in config.status
+ $(SHELL) config.status
+config.status: configure
+ $(SHELL) config.status --recheck
+configure: configure.in
+ cd $(srcdir); autoconf
+config.h.in: configure.in
+ cd $(srcdir); autoheader
+@end example
+
+@node Running configure Scripts, Example, Makefiles, Top
+@chapter Running @code{configure} Scripts
+
+A software package that uses a @code{configure} script generated by
+Autoconf should be distributed with a file @file{Makefile.in}, but no
+@file{Makefile}; that way, the user has to properly configure the
+package for the local system before compiling it. Normally, configuring
+consists of simply doing a @code{cd} to the package's source code
+directory and typing:
+
+@example
+configure
+@end example
+
+If the @code{PATH} environment variable does not contain the directory
+@samp{.}, the command is instead:
+
+@example
+./configure
+@end example
+
+Users running @code{csh} on old versions of System V might have to
+explicitly run @code{sh} on @code{configure}:
+
+@example
+sh configure
+@end example
+
+Running @code{configure} takes a minute or two. While it is running, it
+prints some messages that tell what it is doing. If you don't want to
+see the messages, run @code{configure} with its standard output
+redirected to @file{/dev/null}; for example, @samp{./configure >/dev/null}.
+
+To compile the package in a different directory from the one containing
+the source code, you must use a version of @code{make} that supports the
+@code{VPATH} variable, such as GNU @code{make}. @code{cd} to the
+directory where you want the object files and executables to go and run
+@code{configure}. @code{configure} automatically checks for the source
+code in the directory that @code{configure} is in and in @file{..}. If
+for some reason @code{configure} is not in the source code directory
+that you are configuring, then it will report that it can't find the
+source code. In that case, run @code{configure} with the option
+@samp{--srcdir=@var{dir}}, where @var{dir} is the directory that
+contains the source code.
+
+By default, @samp{make install} will install the package's files in
+@file{/usr/local/bin}, @file{/usr/local/man}, etc. You can specify an
+installation prefix other than @file{/usr/local} by giving
+@code{configure} the option @samp{--prefix=@var{path}}. Alternately,
+you can do so by giving a value for the @samp{prefix} variable when you
+run @code{make}, e.g.,
+@example
+make prefix=/usr/gnu
+@end example
+
+You can specify separate installation prefixes for machine-specific
+files and machine-independent files. If you give @code{configure} the
+option @samp{--exec-prefix=@var{path}} or set the @code{make} variable
+@samp{exec_prefix} to @var{path}, the package will use @var{path} as the
+prefix for installing programs and libraries. Normally, all files are
+installed using the same prefix.
+
+Another @code{configure} option is useful mainly in @file{Makefile}
+rules for updating @file{config.status} and @file{Makefile}. The
+@samp{--no-create} option figures out the configuration for your system
+and records it in @file{config.status}, without actually configuring the
+package (creating @file{Makefile}s and perhaps a configuration header
+file). Later, you can run @file{./config.status} to actually configure
+the package. You can also give @file{config.status} the
+@samp{--recheck} option, which makes it re-run @code{configure} with the
+same arguments you used before. This option is useful if you change
+@code{configure}.
+
+Some packages pay attention to @samp{--with-@var{package}} options to
+@code{configure}, where @var{package} is something like @samp{gnu-libc}
+or @samp{x} (for X windows). The README should mention any
+@samp{--with-} options that the package recognizes.
+
+@code{configure} ignores any other arguments that you give it.
+
+On systems that require unusual options for compilation or linking that
+the package's @code{configure} script does not know about, you can give
+@code{configure} initial values for variables by setting them in the
+environment. In Bourne-compatible shells, you can do that on the
+command line like this:
+
+@example
+CC='gcc -traditional' LIBS=-lposix ./configure
+@end example
+
+The @code{make} variables that you might want to override with
+environment variables when running @code{configure} are:
+
+(For these variables, any value given in the environment overrides the
+value that @code{configure} would choose:)
+
+@defvar CC
+C compiler program. The default is @code{cc}, or @code{gcc} if
+@code{gcc} is in your @code{PATH}.
+@end defvar
+
+@defvar INSTALL
+Program to use to install files. The default is @code{install} if you
+have it, @code{cp} otherwise.
+@end defvar
+
+(For these variables, any value given in the environment is added to
+the value that @code{configure} chooses:)
+
+@defvar DEFS
+Configuration options, in the form @samp{-Dfoo -Dbar@dots{}}. Do not
+use this variable in packages that use @code{AC_CONFIG_HEADER}.
+@end defvar
+
+@defvar LIBS
+Libraries to link with, in the form @samp{-lfoo -lbar@dots{}}.
+@end defvar
+
+Of course, in the long term, most problems requiring manual intervention
+should be fixed by updating either the Autoconf macros or the
+@file{configure.in} file for that package. @xref{Making configure
+Scripts}, for a discussion of that subject.
+
+@node Example, Preprocessor Symbol Index, Running configure Scripts, Top
+@chapter An Example
+
+Here are sample @file{configure.in} and @file{Makefile.in} files, to
+give a real illustration of using Autoconf. They are from the GNU
+@code{cpio} package, which also includes the @code{mt} and @code{rmt}
+programs. This package does not use a configuration header file; it
+passes @samp{-D} options to the C compiler on the command line.
+
+@menu
+* Sample configure.in:: An example of a @file{configure} template.
+* Sample Makefile.in:: An example of a @file{Makefile} template.
+@end menu
+
+@node Sample configure.in, Sample Makefile.in, , Example
+@section Sample @file{configure.in}
+
+@noindent
+Here is @file{configure.in} from GNU @code{cpio}. The @code{dnl} macro
+after @code{AC_SUBST} is suppresses an extra (though harmless) newline
+in the generated @code{configure} script (because the @code{AC_SUBST}
+macro does not produce any output where it is called).
+
+@example
+dnl Process this file with autoconf to produce a configure script.
+AC_INIT(cpio.h)
+PROGS="cpio"
+AC_SUBST(PROGS)dnl
+AC_PROG_CC
+AC_PROG_CPP
+AC_GCC_TRADITIONAL
+AC_PROG_INSTALL
+AC_AIX
+AC_MINIX
+AC_ISC_POSIX
+AC_RETSIGTYPE
+AC_MAJOR_HEADER
+AC_REMOTE_TAPE
+test -n "$have_mtio" && PROGS="$PROGS mt"
+AC_RSH
+AC_CONST
+AC_UID_T
+AC_STDC_HEADERS
+AC_UNISTD_H
+AC_HAVE_HEADERS(string.h fcntl.h utime.h sys/io/trioctl.h)
+AC_REPLACE_FUNCS(fnmatch bcopy mkdir strdup)
+AC_HAVE_FUNCS(strerror lchown)
+AC_VPRINTF
+AC_ALLOCA
+AC_XENIX_DIR
+AC_HAVE_LIBRARY(socket, [LIBS="$LIBS -lsocket"])
+AC_HAVE_LIBRARY(nsl, [LIBS="$LIBS -lnsl"])
+AC_OUTPUT(Makefile)
+@end example
+
+@node Sample Makefile.in, , Sample configure.in, Example
+@section Sample @file{Makefile.in}
+
+@noindent
+Here is @file{Makefile.in} from GNU @code{cpio}, with some irrelevant
+lines omitted, for brevity.
+
+@example
+srcdir = @@srcdir@@
+VPATH = @@srcdir@@
+
+CC = @@CC@@
+
+INSTALL = @@INSTALL@@
+INSTALL_PROGRAM = @@INSTALL_PROGRAM@@
+INSTALL_DATA = @@INSTALL_DATA@@
+
+DEFS = @@DEFS@@
+LIBS = @@LIBS@@
+RTAPELIB = @@RTAPELIB@@
+
+CFLAGS = -g
+LDFLAGS = -g
+
+prefix = /usr/local
+exec_prefix = $(prefix)
+binprefix =
+manprefix =
+
+bindir = $(exec_prefix)/bin
+libdir = $(exec_prefix)/lib
+mandir = $(prefix)/man/man1
+manext = 1
+
+SHELL = /bin/sh
+
+SRCS = copyin.c copyout.c copypass.c defer.c dstring.c global.c \
+main.c tar.c util.c error.c getopt.c getopt1.c filemode.c version.c \
+rtapelib.c dirname.c idcache.c makepath.c xmalloc.c stripslash.c \
+userspec.c xstrdup.c bcopy.c fnmatch.c mkdir.c strdup.c
+OBJS = copyin.o copyout.o copypass.o defer.o dstring.o global.o \
+main.o tar.o util.o error.o getopt.o getopt1.o filemode.o version.o \
+$(RTAPELIB) dirname.o idcache.o makepath.o xmalloc.o stripslash.o \
+userspec.o xstrdup.o @@LIBOBJS@@ @@ALLOCA@@
+# mt source files not shared with cpio.
+MT_SRCS = mt.c argmatch.c
+MT_OBJS = mt.o argmatch.o error.o getopt.o getopt1.o \
+xmalloc.o version.o $(RTAPELIB) @@ALLOCA@@
+HDRS = cpio.h cpiohdr.h tar.h tarhdr.h defer.h dstring.h extern.h filetypes.h \
+system.h fnmatch.h getopt.h rmt.h
+DISTFILES = $(SRCS) $(HDRS) COPYING COPYING.LIB ChangeLog Makefile.in \
+README NEWS INSTALL cpio.1 mt.1 makefile.pc makefile.os2 cpio.def \
+configure configure.in mkinstalldirs $(MT_SRCS) rmt.c tcexparg.c alloca.c
+
+all: @@PROGS@@
+
+.c.o:
+ $(CC) -c $(CPPFLAGS) $(DEFS) -I$(srcdir) $(CFLAGS) $<
+
+install: installdirs all $(srcdir)/cpio.1 $(srcdir)/mt.1
+ $(INSTALL_PROGRAM) cpio $(bindir)/$(binprefix)cpio
+ test ! -f mt || $(INSTALL_PROGRAM) mt $(bindir)/$(binprefix)mt
+ -test ! -f rmt || $(INSTALL_PROGRAM) rmt $(libdir)/rmt
+ $(INSTALL_DATA) $(srcdir)/cpio.1 $(mandir)/$(manprefix)cpio.$(manext)
+ test ! -f mt || \
+ $(INSTALL_DATA) $(srcdir)/mt.1 $(mandir)/$(manprefix)mt.$(manext)
+
+installdirs:
+ $(srcdir)/mkinstalldirs $(bindir) $(libdir) $(mandir)
+
+uninstall:
+ cd $(bindir); rm -f $(binprefix)cpio $(binprefix)mt
+ -rm -f $(libdir)/rmt
+ cd $(mandir); rm -f $(manprefix)cpio.$(manext) $(manprefix)mt.$(manext)
+
+check:
+ @@echo No tests are supplied.
+
+cpio: $(OBJS)
+ $(CC) $(LDFLAGS) -o $@@ $(OBJS) $(LIBS)
+
+rmt: rmt.o
+ $(CC) $(LDFLAGS) -o $@@ rmt.o $(LIBS)
+
+mt: $(MT_OBJS)
+ $(CC) $(LDFLAGS) -o $@@ $(MT_OBJS) $(LIBS)
+
+Makefile: Makefile.in config.status
+ $(SHELL) config.status
+config.status: configure
+ $(SHELL) config.status --recheck
+configure: configure.in
+ cd $(srcdir); autoconf
+
+TAGS: $(SRCS)
+ etags $(SRCS)
+
+clean:
+ rm -f cpio rmt mt *.o core
+
+mostlyclean: clean
+
+distclean: clean
+ rm -f Makefile config.status
+
+realclean: distclean
+ rm -f TAGS
+
+dist: $(DISTFILES)
+ echo cpio-`sed -e '/version_string/!d' \
+ -e 's/[^0-9.]*\([0-9.]*\).*/\1/' -e q version.c` > .fname
+ rm -rf `cat .fname`
+ mkdir `cat .fname`
+ -ln $(DISTFILES) `cat .fname`
+ for file in $(DISTFILES); do \
+ test -r `cat .fname`/$$file || cp -p $$file `cat .fname`; \
+ done
+ tar chzf `cat .fname`.tar.gz `cat .fname`
+ rm -rf `cat .fname` .fname
+@end example
+
+@node Preprocessor Symbol Index, Macro Index, Example, Top
+@unnumbered Preprocessor Symbol Index
+
+This is an alphabetical list of the C preprocessor symbols that the
+Autoconf macros define. To work with Autoconf, C source code needs to
+use these names in @code{#if} directives.
+
+@printindex vr
+
+@node Macro Index, , Preprocessor Symbol Index, Top
+@unnumbered Macro Index
+
+This is an alphabetical list of the Autoconf macros. To make the list
+easier to use, the macros are listed without their preceding @samp{AC_}.
+
+@printindex fn
+
+@contents
+@bye
+
+@c Local variables:
+@c compile-command: "makeinfo --no-split autoconf.texi"
+@c End:
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