Editing: Config.pod

=head1 NAME

=for comment  Generated by configpm.  Any changes made here will be lost!

Config - access Perl configuration information

=head1 SYNOPSIS

use Config;
    if ($Config{usethreads}) {
	print "has thread support\n"
    }

use Config qw(myconfig config_sh config_vars config_re);

print myconfig();

print config_sh();

print config_re();

config_vars(qw(osname archname));

=head1 DESCRIPTION

The Config module contains all the information that was available to
the C<Configure> program at Perl build time (over 900 values).

Shell variables from the F<config.sh> file (written by Configure) are
stored in the readonly-variable C<%Config>, indexed by their names.

Values stored in config.sh as 'undef' are returned as undefined
values. The perl C<exists> function can be used to check if a
named variable exists.

For a description of the variables, please have a look at the
Glossary file, as written in the Porting folder, or use the url:
https://github.com/Perl/perl5/blob/blead/Porting/Glossary

=over 4

=item myconfig()

Returns a textual summary of the major perl configuration values.
See also C<-V> in L<perlrun/Command Switches>.

=item config_sh()

Returns the entire perl configuration information in the form of the
original config.sh shell variable assignment script.

=item config_re($regex)

Like config_sh() but returns, as a list, only the config entries who's
names match the $regex.

=item config_vars(@names)

Prints to STDOUT the values of the named configuration variable. Each is
printed on a separate line in the form:

name='value';

Names which are unknown are output as C<name='UNKNOWN';>.
See also C<-V:name> in L<perlrun/Command Switches>.

=item bincompat_options()

Returns a list of C pre-processor options used when compiling this F<perl>
binary, which affect its binary compatibility with extensions.
C<bincompat_options()> and C<non_bincompat_options()> are shown together in
the output of C<perl -V> as I<Compile-time options>.

=item non_bincompat_options()

Returns a list of C pre-processor options used when compiling this F<perl>
binary, which do not affect binary compatibility with extensions.

=item compile_date()

Returns the compile date (as a string), equivalent to what is shown by
C<perl -V>

=item local_patches()

Returns a list of the names of locally applied patches, equivalent to what
is shown by C<perl -V>.

=item header_files()

Returns a list of the header files that should be used as dependencies for
XS code, for this version of Perl on this platform.

=back

=head1 EXAMPLE

Here's a more sophisticated example of using %Config:

use Config;
    use strict;

my %sig_num;
    my @sig_name;
    unless($Config{sig_name} && $Config{sig_num}) {
	die "No sigs?";
    } else {
	my @names = split ' ', $Config{sig_name};
	@sig_num{@names} = split ' ', $Config{sig_num};
	foreach (@names) {
	    $sig_name[$sig_num{$_}] ||= $_;
	}   
    }

print "signal #17 = $sig_name[17]\n";
    if ($sig_num{ALRM}) { 
	print "SIGALRM is $sig_num{ALRM}\n";
    }

=head1 WARNING

Because this information is not stored within the perl executable
itself it is possible (but unlikely) that the information does not
relate to the actual perl binary which is being used to access it.

The Config module is installed into the architecture and version
specific library directory ($Config{installarchlib}) and it checks the
perl version number when loaded.

The values stored in config.sh may be either single-quoted or
double-quoted. Double-quoted strings are handy for those cases where you
need to include escape sequences in the strings. To avoid runtime variable
interpolation, any C<$> and C<@> characters are replaced by C<\$> and
C<\@>, respectively. This isn't foolproof, of course, so don't embed C<\$>
or C<\@> in double-quoted strings unless you're willing to deal with the
consequences. (The slashes will end up escaped and the C<$> or C<@> will
trigger variable interpolation)

=head1 GLOSSARY

Most C<Config> variables are determined by the C<Configure> script
on platforms supported by it (which is most UNIX platforms). Some
platforms have custom-made C<Config> variables, and may thus not have
some of the variables described below, or may have extraneous variables
specific to that particular port. See the port specific documentation
in such cases.

=cut

=head2 _

=over 4

=item C<_a>

From F<Unix.U>:

This variable defines the extension used for ordinary library files.
For unix, it is F<.a>. The F<.> is included. Other possible
values include F<.lib>.

=item C<_exe>

From F<Unix.U>:

This variable defines the extension used for executable files.
C<DJGPP>, Cygwin and F<OS/2> use F<.exe>. Stratus C<VOS> uses F<.pm>.
On operating systems which do not require a specific extension
for executable files, this variable is empty.

=item C<_o>

From F<Unix.U>:

This variable defines the extension used for object files.
For unix, it is F<.o>. The F<.> is included. Other possible
values include F<.obj>.

=back

=head2 a

=over 4

=item C<afs>

From F<afs.U>:

This variable is set to C<true> if C<AFS> (Andrew File System) is used
on the system, C<false> otherwise. It is possible to override this
with a hint value or command line option, but you'd better know
what you are doing.

=item C<afsroot>

From F<afs.U>:

This variable is by default set to F</afs>. In the unlikely case
this is not the correct root, it is possible to override this with
a hint value or command line option. This will be used in subsequent
tests for AFSness in the configure and test process.

=item C<alignbytes>

From F<alignbytes.U>:

This variable holds the number of bytes required to align a
double-- or a long double when applicable. Usual values are
2, 4 and 8.  The default is eight, for safety.

=item C<aphostname>

From F<d_gethname.U>:

This variable contains the command which can be used to compute the
host name. The command is fully qualified by its absolute path, to make
it safe when used by a process with super-user privileges.

=item C<api_revision>

From F<patchlevel.U>:

The three variables, api_revision, api_version, and
api_subversion, specify the version of the oldest perl binary
compatible with the present perl. In a full version string
such as F<5.6.1>, api_revision is the C<5>.
Prior to 5.5.640, the format was a floating point number,
like 5.00563.

F<perl.c>:incpush() and F<lib/lib.pm> will automatically search in
F<$sitelib/.>. for older directories back to the limit specified
by these api_ variables. This is only useful if you have a
perl library directory tree structured like the default one.
See C<INSTALL> for how this works. The versioned site_perl
directory was introduced in 5.005, so that is the lowest
possible value. The version list appropriate for the current
system is determined in F<inc_version_list.U>.

C<XXX> To do: Since compatibility can depend on compile time
options (such as bincompat, longlong, etc.) it should
(perhaps) be set by Configure, but currently it isn't.
Currently, we read a hard-wired value from F<patchlevel.h>.
Perhaps what we ought to do is take the hard-wired value from
F<patchlevel.h> but then modify it if the current Configure
options warrant. F<patchlevel.h> then would use an #ifdef guard.

=item C<api_subversion>

From F<patchlevel.U>:

=item C<api_version>

From F<patchlevel.U>:

The three variables, api_revision, api_version, and
api_subversion, specify the version of the oldest perl binary
compatible with the present perl. In a full version string
such as F<5.6.1>, api_version is the C<6>. See api_revision for
full details. As a special case, 5.5.0 is rendered in the
old-style as 5.005. (In the 5.005_0x maintenance series,
this was the only versioned directory in $sitelib.)

=item C<api_versionstring>

From F<patchlevel.U>:

This variable combines api_revision, api_version, and
api_subversion in a format such as 5.6.1 (or 5_6_1) suitable
for use as a directory name.  This is filesystem dependent.

=item C<ar>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the ar program. After Configure runs,
the value is reset to a plain C<ar> and is not useful.

=item C<archlib>

From F<archlib.U>:

This variable holds the name of the directory in which the user wants
to put architecture-dependent public library files for $package.
It is most often a local directory such as F</usr/local/lib>.
Programs using this variable must be prepared to deal
with filename expansion.

=item C<archlibexp>

From F<archlib.U>:

This variable is the same as the archlib variable, but is
filename expanded at configuration time, for convenient use.

=item C<archname>

From F<archname.U>:

This variable is a short name to characterize the current
architecture.  It is used mainly to construct the default archlib.

=item C<archname64>

From F<use64bits.U>:

This variable is used for the 64-bitness part of $archname.

=item C<archobjs>

From F<Unix.U>:

This variable defines any additional objects that must be linked
in with the program on this architecture. On unix, it is usually
empty. It is typically used to include emulations of unix calls
or other facilities. For perl on F<OS/2>, for example, this would
include F<os2/os2.obj>.

=item C<asctime_r_proto>

From F<d_asctime_r.U>:

This variable encodes the prototype of asctime_r.
It is zero if d_asctime_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_asctime_r
is defined.

=item C<awk>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the awk program. After Configure runs,
the value is reset to a plain C<awk> and is not useful.

=back

=head2 b

=over 4

=item C<baserev>

From F<baserev.U>:

The base revision level of this package, from the F<.package> file.

=item C<bash>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<bin>

From F<bin.U>:

This variable holds the name of the directory in which the user wants
to put publicly executable images for the package in question. It
is most often a local directory such as F</usr/local/bin>. Programs using
this variable must be prepared to deal with F<~name> substitution.

=item C<bin_ELF>

From F<dlsrc.U>:

This variable saves the result from configure if generated binaries
are in C<ELF> format. Only set to defined when the test has actually
been performed, and the result was positive.

=item C<binexp>

From F<bin.U>:

This is the same as the bin variable, but is filename expanded at
configuration time, for use in your makefiles.

=item C<bison>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the bison program. After Configure runs,
the value is reset to a plain C<bison> and is not useful.

=item C<byacc>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the byacc program. After Configure runs,
the value is reset to a plain C<byacc> and is not useful.

=item C<byteorder>

From F<byteorder.U>:

This variable holds the byte order in a C<UV>. In the following,
larger digits indicate more significance. The variable byteorder
is either 4321 on a big-endian machine, or 1234 on a little-endian,
or 87654321 on a Cray ... or 3412 with weird order !

=back

=head2 c

=over 4

=item C<c>

From F<n.U>:

This variable contains the \c string if that is what causes the echo
command to suppress newline.  Otherwise it is null.  Correct usage is
$echo $n "prompt for a question: $c".

=item C<castflags>

From F<d_castneg.U>:

This variable contains a flag that precise difficulties the
compiler has casting odd floating values to unsigned long:
0 = ok
1 = couldn't cast < 0
2 = couldn't cast >= 0x80000000
4 = couldn't cast in argument expression list

=item C<cat>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the cat program. After Configure runs,
the value is reset to a plain C<cat> and is not useful.

=item C<cc>

From F<cc.U>:

This variable holds the name of a command to execute a C compiler which
can resolve multiple global references that happen to have the same
name. Usual values are C<cc> and C<gcc>.
Fervent C<ANSI> compilers may be called C<c89>. C<AIX> has xlc.

=item C<cccdlflags>

From F<dlsrc.U>:

This variable contains any special flags that might need to be
passed with C<cc -c> to compile modules to be used to create a shared
library that will be used for dynamic loading. For hpux, this
should be +z. It is up to the makefile to use it.

=item C<ccdlflags>

From F<dlsrc.U>:

This variable contains any special flags that might need to be
passed to cc to link with a shared library for dynamic loading.
It is up to the makefile to use it.  For sunos 4.1, it should
be empty.

=item C<ccflags>

From F<ccflags.U>:

This variable contains any additional C compiler flags desired by
the user.  It is up to the Makefile to use this.

=item C<ccflags_uselargefiles>

From F<uselfs.U>:

This variable contains the compiler flags needed by large file builds
and added to ccflags by hints files.

=item C<ccname>

From F<Checkcc.U>:

This can set either by hints files or by Configure. If using
gcc, this is gcc, and if not, usually equal to cc, unimpressive, no?
Some platforms, however, make good use of this by storing the
flavor of the C compiler being used here. For example if using
the Sun WorkShop suite, ccname will be C<workshop>.

=item C<ccsymbols>

From F<Cppsym.U>:

The variable contains the symbols defined by the C compiler alone.
The symbols defined by cpp or by cc when it calls cpp are not in
this list, see cppsymbols and cppccsymbols.
The list is a space-separated list of symbol=value tokens.

=item C<ccversion>

From F<Checkcc.U>:

This can set either by hints files or by Configure.  If using
a (non-gcc) vendor cc, this variable may contain a version for
the compiler.

=item C<cf_by>

From F<cf_who.U>:

Login name of the person who ran the Configure script and answered the
questions. This is used to tag both F<config.sh> and F<config_h.SH>.

=item C<cf_email>

From F<cf_email.U>:

Electronic mail address of the person who ran Configure. This can be
used by units that require the user's e-mail, like F<MailList.U>.

=item C<cf_time>

From F<cf_who.U>:

Holds the output of the C<date> command when the configuration file was
produced. This is used to tag both F<config.sh> and F<config_h.SH>.

=item C<charbits>

From F<charsize.U>:

This variable contains the value of the C<CHARBITS> symbol, which
indicates to the C program how many bits there are in a character.

=item C<charsize>

From F<charsize.U>:

This variable contains the value of the C<CHARSIZE> symbol, which
indicates to the C program how many bytes there are in a character.

=item C<chgrp>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<chmod>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the chmod program. After Configure runs,
the value is reset to a plain C<chmod> and is not useful.

=item C<chown>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<clocktype>

From F<d_times.U>:

This variable holds the type returned by times(). It can be long,
or clock_t on C<BSD> sites (in which case <sys/types.h> should be
included).

=item C<comm>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the comm program. After Configure runs,
the value is reset to a plain C<comm> and is not useful.

=item C<compress>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<config_arg0>

From F<Options.U>:

This variable contains the string used to invoke the Configure
command, as reported by the shell in the $0 variable.

=item C<config_argc>

From F<Options.U>:

This variable contains the number of command-line arguments
passed to Configure, as reported by the shell in the $# variable.
The individual arguments are stored as variables config_arg1,
config_arg2, etc.

=item C<config_args>

From F<Options.U>:

This variable contains a single string giving the command-line
arguments passed to Configure.	Spaces within arguments,
quotes, and escaped characters are not correctly preserved.
To reconstruct the command line, you must assemble the individual
command line pieces, given in config_arg[0-9]*.

=item C<contains>

From F<contains.U>:

This variable holds the command to do a grep with a proper return
status. On most sane systems it is simply C<grep>. On insane systems
it is a grep followed by a cat followed by a test. This variable
is primarily for the use of other Configure units.

=item C<cp>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the cp program. After Configure runs,
the value is reset to a plain C<cp> and is not useful.

=item C<cpio>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<cpp>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the cpp program. After Configure runs,
the value is reset to a plain C<cpp> and is not useful.

=item C<cpp_stuff>

From F<cpp_stuff.U>:

This variable contains an identification of the concatenation mechanism
used by the C preprocessor.

=item C<cppccsymbols>

From F<Cppsym.U>:

The variable contains the symbols defined by the C compiler
when it calls cpp.  The symbols defined by the cc alone or cpp
alone are not in this list, see ccsymbols and cppsymbols.
The list is a space-separated list of symbol=value tokens.

=item C<cppflags>

From F<ccflags.U>:

This variable holds the flags that will be passed to the C pre-
processor. It is up to the Makefile to use it.

=item C<cpplast>

From F<cppstdin.U>:

This variable has the same functionality as cppminus, only it applies
to cpprun and not cppstdin.

=item C<cppminus>

From F<cppstdin.U>:

This variable contains the second part of the string which will invoke
the C preprocessor on the standard input and produce to standard
output. This variable will have the value C<-> if cppstdin needs
a minus to specify standard input, otherwise the value is "".

=item C<cpprun>

From F<cppstdin.U>:

This variable contains the command which will invoke a C preprocessor
on standard input and put the output to stdout. It is guaranteed not
to be a wrapper and may be a null string if no preprocessor can be
made directly available. This preprocessor might be different from the
one used by the C compiler. Don't forget to append cpplast after the
preprocessor options.

=item C<cppstdin>

From F<cppstdin.U>:

This variable contains the command which will invoke the C
preprocessor on standard input and put the output to stdout.
It is primarily used by other Configure units that ask about
preprocessor symbols.

=item C<cppsymbols>

From F<Cppsym.U>:

The variable contains the symbols defined by the C preprocessor
alone.  The symbols defined by cc or by cc when it calls cpp are
not in this list, see ccsymbols and cppccsymbols.
The list is a space-separated list of symbol=value tokens.

=item C<crypt_r_proto>

From F<d_crypt_r.U>:

This variable encodes the prototype of crypt_r.
It is zero if d_crypt_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_crypt_r
is defined.

=item C<cryptlib>

From F<d_crypt.U>:

This variable holds -lcrypt or the path to a F<libcrypt.a> archive if
the crypt() function is not defined in the standard C library. It is
up to the Makefile to use this.

=item C<csh>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the csh program. After Configure runs,
the value is reset to a plain C<csh> and is not useful.

=item C<ctermid_r_proto>

From F<d_ctermid_r.U>:

This variable encodes the prototype of ctermid_r.
It is zero if d_ctermid_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_ctermid_r
is defined.

=item C<ctime_r_proto>

From F<d_ctime_r.U>:

This variable encodes the prototype of ctime_r.
It is zero if d_ctime_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_ctime_r
is defined.

=back

=head2 d

=over 4

=item C<d__fwalk>

From F<d__fwalk.U>:

This variable conditionally defines C<HAS__FWALK> if _fwalk() is
available to apply a function to all the file handles.

=item C<d_accept4>

From F<d_accept4.U>:

This variable conditionally defines HAS_ACCEPT4 if accept4() is
available to accept socket connections.

=item C<d_access>

From F<d_access.U>:

This variable conditionally defines C<HAS_ACCESS> if the access() system
call is available to check for access permissions using real IDs.

=item C<d_accessx>

From F<d_accessx.U>:

This variable conditionally defines the C<HAS_ACCESSX> symbol, which
indicates to the C program that the accessx() routine is available.

=item C<d_acosh>

From F<d_acosh.U>:

This variable conditionally defines the C<HAS_ACOSH> symbol, which
indicates to the C program that the acosh() routine is available.

=item C<d_aintl>

From F<d_aintl.U>:

This variable conditionally defines the C<HAS_AINTL> symbol, which
indicates to the C program that the aintl() routine is available.
If copysignl is also present we can emulate modfl.

=item C<d_alarm>

From F<d_alarm.U>:

This variable conditionally defines the C<HAS_ALARM> symbol, which
indicates to the C program that the alarm() routine is available.

=item C<d_archlib>

From F<archlib.U>:

This variable conditionally defines C<ARCHLIB> to hold the pathname
of architecture-dependent library files for $package. If
$archlib is the same as $privlib, then this is set to undef.

=item C<d_asctime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_ASCTIME64 symbol, which
indicates to the C program that the asctime64 () routine is available.

=item C<d_asctime_r>

From F<d_asctime_r.U>:

This variable conditionally defines the C<HAS_ASCTIME_R> symbol,
which indicates to the C program that the asctime_r()
routine is available.

=item C<d_asinh>

From F<d_asinh.U>:

This variable conditionally defines the C<HAS_ASINH> symbol, which
indicates to the C program that the asinh() routine is available.

=item C<d_atanh>

From F<d_atanh.U>:

This variable conditionally defines the C<HAS_ATANH> symbol, which
indicates to the C program that the atanh() routine is available.

=item C<d_atolf>

From F<atolf.U>:

This variable conditionally defines the C<HAS_ATOLF> symbol, which
indicates to the C program that the atolf() routine is available.

=item C<d_atoll>

From F<atoll.U>:

This variable conditionally defines the C<HAS_ATOLL> symbol, which
indicates to the C program that the atoll() routine is available.

=item C<d_attribute_deprecated>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_DEPRECATED>, which
indicates that C<GCC> can handle the attribute for marking deprecated
APIs

=item C<d_attribute_format>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_FORMAT>, which
indicates the C compiler can check for printf-like formats.

=item C<d_attribute_malloc>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_MALLOC>, which
indicates the C compiler can understand functions as having
malloc-like semantics.

=item C<d_attribute_nonnull>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_NONNULL>, which
indicates that the C compiler can know that certain arguments
must not be C<NULL>, and will check accordingly at compile time.

=item C<d_attribute_noreturn>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_NORETURN>, which
indicates that the C compiler can know that certain functions
are guaranteed never to return.

=item C<d_attribute_pure>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_PURE>, which
indicates that the C compiler can know that certain functions
are C<pure> functions, meaning that they have no side effects, and
only rely on function input F<and/or> global data for their results.

=item C<d_attribute_unused>

From F<d_attribut.U>:

This variable conditionally defines C<HASATTRIBUTE_UNUSED>, which
indicates that the C compiler can know that certain variables
and arguments may not always be used, and to not throw warnings
if they don't get used.

=item C<d_attribute_warn_unused_result>

From F<d_attribut.U>:

This variable conditionally defines
C<HASATTRIBUTE_WARN_UNUSED_RESULT>, which indicates that the C
compiler can know that certain functions have a return values
that must not be ignored, such as malloc() or open().

=item C<d_backtrace>

From F<d_backtrace.U>:

This variable conditionally defines the C<HAS_BACKTRACE> symbol, which
indicates to the C program that the backtrace() routine is available
to get a stack trace.

=item C<d_bsd>

From F<Guess.U>:

This symbol conditionally defines the symbol C<BSD> when running on a
C<BSD> system.

=item C<d_bsdgetpgrp>

From F<d_getpgrp.U>:

This variable conditionally defines C<USE_BSD_GETPGRP> if
getpgrp needs one arguments whereas C<USG> one needs none.

=item C<d_bsdsetpgrp>

From F<d_setpgrp.U>:

This variable conditionally defines C<USE_BSD_SETPGRP> if
setpgrp needs two arguments whereas C<USG> one needs none.
See also d_setpgid for a C<POSIX> interface.

=item C<d_builtin_add_overflow>

From F<d_builtin_overflow.U>:

This variable conditionally defines C<HAS_BUILTIN_ADD_OVERFLOW>, which
indicates that the compiler supports __builtin_add_overflow(x,y,&z)
for safely adding x and y into z while checking for overflow.

=item C<d_builtin_choose_expr>

From F<d_builtin.U>:

This conditionally defines C<HAS_BUILTIN_CHOOSE_EXPR>, which
indicates that the compiler supports __builtin_choose_expr(x,y,z).
This built-in function is analogous to the C<x?y:z> operator in C,
except that the expression returned has its type unaltered by
promotion rules. Also, the built-in function does not evaluate
the expression that was not chosen.

=item C<d_builtin_expect>

From F<d_builtin.U>:

This conditionally defines C<HAS_BUILTIN_EXPECT>, which indicates
that the compiler supports __builtin_expect(exp,c). You may use
__builtin_expect to provide the compiler with branch prediction
information.

=item C<d_builtin_mul_overflow>

From F<d_builtin_overflow.U>:

This variable conditionally defines C<HAS_BUILTIN_MUL_OVERFLOW>, which
indicates that the compiler supports __builtin_mul_overflow(x,y,&z)
for safely multiplying x and y into z while checking for overflow.

=item C<d_builtin_sub_overflow>

From F<d_builtin_overflow.U>:

This variable conditionally defines C<HAS_BUILTIN_SUB_OVERFLOW>, which
indicates that the compiler supports __builtin_sub_overflow(x,y,&z)
for safely subtracting y from x into z while checking for overflow.

=item C<d_c99_variadic_macros>

From F<d_c99_variadic.U>:

This variable conditionally defines the HAS_C99_VARIADIC_MACROS
symbol, which indicates to the C program that C99 variadic macros
are available.

=item C<d_casti32>

From F<d_casti32.U>:

This variable conditionally defines CASTI32, which indicates
whether the C compiler can cast large floats to 32-bit ints.

=item C<d_castneg>

From F<d_castneg.U>:

This variable conditionally defines C<CASTNEG>, which indicates
whether the C compiler can cast negative float to unsigned.

=item C<d_cbrt>

From F<d_cbrt.U>:

This variable conditionally defines the C<HAS_CBRT> symbol, which
indicates to the C program that the cbrt() (cube root) function
is available.

=item C<d_chown>

From F<d_chown.U>:

This variable conditionally defines the C<HAS_CHOWN> symbol, which
indicates to the C program that the chown() routine is available.

=item C<d_chroot>

From F<d_chroot.U>:

This variable conditionally defines the C<HAS_CHROOT> symbol, which
indicates to the C program that the chroot() routine is available.

=item C<d_chsize>

From F<d_chsize.U>:

This variable conditionally defines the C<CHSIZE> symbol, which
indicates to the C program that the chsize() routine is available
to truncate files. You might need a -lx to get this routine.

=item C<d_class>

From F<d_class.U>:

This variable conditionally defines the C<HAS_CLASS> symbol, which
indicates to the C program that the class() routine is available.

=item C<d_clearenv>

From F<d_clearenv.U>:

This variable conditionally defines the C<HAS_CLEARENV> symbol, which
indicates to the C program that the clearenv () routine is available.

=item C<d_closedir>

From F<d_closedir.U>:

This variable conditionally defines C<HAS_CLOSEDIR> if closedir() is
available.

=item C<d_cmsghdr_s>

From F<d_cmsghdr_s.U>:

This variable conditionally defines the C<HAS_STRUCT_CMSGHDR> symbol,
which indicates that the struct cmsghdr is supported.

=item C<d_copysign>

From F<d_copysign.U>:

This variable conditionally defines the C<HAS_COPYSIGN> symbol, which
indicates to the C program that the copysign() routine is available.

=item C<d_copysignl>

From F<d_copysignl.U>:

This variable conditionally defines the C<HAS_COPYSIGNL> symbol, which
indicates to the C program that the copysignl() routine is available.
If aintl is also present we can emulate modfl.

=item C<d_cplusplus>

From F<d_cplusplus.U>:

This variable conditionally defines the C<USE_CPLUSPLUS> symbol, which
indicates that a C++ compiler was used to compiled Perl and will be
used to compile extensions.

=item C<d_crypt>

From F<d_crypt.U>:

This variable conditionally defines the C<CRYPT> symbol, which
indicates to the C program that the crypt() routine is available
to encrypt passwords and the like.

=item C<d_crypt_r>

From F<d_crypt_r.U>:

This variable conditionally defines the C<HAS_CRYPT_R> symbol,
which indicates to the C program that the crypt_r()
routine is available.

=item C<d_csh>

From F<d_csh.U>:

This variable conditionally defines the C<CSH> symbol, which
indicates to the C program that the C-shell exists.

=item C<d_ctermid>

From F<d_ctermid.U>:

This variable conditionally defines C<CTERMID> if ctermid() is
available to generate filename for terminal.

=item C<d_ctermid_r>

From F<d_ctermid_r.U>:

This variable conditionally defines the C<HAS_CTERMID_R> symbol,
which indicates to the C program that the ctermid_r()
routine is available.

=item C<d_ctime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_CTIME64 symbol, which
indicates to the C program that the ctime64 () routine is available.

=item C<d_ctime_r>

From F<d_ctime_r.U>:

This variable conditionally defines the C<HAS_CTIME_R> symbol,
which indicates to the C program that the ctime_r()
routine is available.

=item C<d_cuserid>

From F<d_cuserid.U>:

This variable conditionally defines the C<HAS_CUSERID> symbol, which
indicates to the C program that the cuserid() routine is available
to get character login names.

=item C<d_dbminitproto>

From F<d_dbminitproto.U>:

This variable conditionally defines the C<HAS_DBMINIT_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the dbminit() function. Otherwise, it is
up to the program to supply one.

=item C<d_difftime>

From F<d_difftime.U>:

This variable conditionally defines the C<HAS_DIFFTIME> symbol, which
indicates to the C program that the difftime() routine is available.

=item C<d_difftime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_DIFFTIME64 symbol, which
indicates to the C program that the difftime64 () routine is available.

=item C<d_dir_dd_fd>

From F<d_dir_dd_fd.U>:

This variable conditionally defines the C<HAS_DIR_DD_FD> symbol, which
indicates that the C<DIR> directory stream type contains a member
variable called dd_fd.

=item C<d_dirfd>

From F<d_dirfd.U>:

This variable conditionally defines the C<HAS_DIRFD> constant,
which indicates to the C program that dirfd() is available
to return the file descriptor of a directory stream.

=item C<d_dirnamlen>

From F<i_dirent.U>:

This variable conditionally defines C<DIRNAMLEN>, which indicates
to the C program that the length of directory entry names is
provided by a d_namelen field.

=item C<d_dladdr>

From F<d_dladdr.U>:

This variable conditionally defines the C<HAS_DLADDR> symbol, which
indicates to the C program that the dladdr() routine is available
to get a stack trace.

=item C<d_dlerror>

From F<d_dlerror.U>:

This variable conditionally defines the C<HAS_DLERROR> symbol, which
indicates to the C program that the dlerror() routine is available.

=item C<d_dlopen>

From F<d_dlopen.U>:

This variable conditionally defines the C<HAS_DLOPEN> symbol, which
indicates to the C program that the dlopen() routine is available.

=item C<d_dlsymun>

From F<d_dlsymun.U>:

This variable conditionally defines C<DLSYM_NEEDS_UNDERSCORE>, which
indicates that we need to prepend an underscore to the symbol
name before calling dlsym().

=item C<d_dosuid>

From F<d_dosuid.U>:

This variable conditionally defines the symbol C<DOSUID>, which
tells the C program that it should insert setuid emulation code
on hosts which have setuid #! scripts disabled.

=item C<d_double_has_inf>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_HAS_INF>
which indicates that the double type has an infinity.

=item C<d_double_has_nan>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_HAS_NAN>
which indicates that the double type has a not-a-number.

=item C<d_double_has_negative_zero>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_HAS_NEGATIVE_ZERO>
which indicates that the double type has a negative zero.

=item C<d_double_has_subnormals>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_HAS_SUBNORMALS>
which indicates that the double type has subnormals (denormals).

=item C<d_double_style_cray>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_STYLE_CRAY>
which indicates that the double is the 64-bit C<CRAY> mainframe format.

=item C<d_double_style_ibm>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_STYLE_IBM>,
which indicates that the double is the 64-bit C<IBM> mainframe format.

=item C<d_double_style_ieee>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_STYLE_IEEE>,
which indicates that the double is the 64-bit C<IEEE> 754.

=item C<d_double_style_vax>

From F<longdblfio.U>:

This variable conditionally defines the symbol C<DOUBLE_STYLE_VAX>,
which indicates that the double is the 64-bit C<VAX> format D or G.

=item C<d_drand48_r>

From F<d_drand48_r.U>:

This variable conditionally defines the HAS_DRAND48_R symbol,
which indicates to the C program that the drand48_r()
routine is available.

=item C<d_drand48proto>

From F<d_drand48proto.U>:

This variable conditionally defines the HAS_DRAND48_PROTO symbol,
which indicates to the C program that the system provides
a prototype for the drand48() function.  Otherwise, it is
up to the program to supply one.

=item C<d_dup2>

From F<d_dup2.U>:

This variable conditionally defines HAS_DUP2 if dup2() is
available to duplicate file descriptors.

=item C<d_dup3>

From F<d_dup3.U>:

This variable conditionally defines HAS_DUP3 if dup3() is
available to duplicate file descriptors.

=item C<d_duplocale>

From F<d_newlocale.U>:

This variable conditionally defines the C<HAS_DUPLOCALE> symbol, which
indicates to the C program that the duplocale() routine is available
to duplicate a locale object.

=item C<d_eaccess>

From F<d_eaccess.U>:

This variable conditionally defines the C<HAS_EACCESS> symbol, which
indicates to the C program that the eaccess() routine is available.

=item C<d_endgrent>

From F<d_endgrent.U>:

This variable conditionally defines the C<HAS_ENDGRENT> symbol, which
indicates to the C program that the endgrent() routine is available
for sequential access of the group database.

=item C<d_endgrent_r>

From F<d_endgrent_r.U>:

This variable conditionally defines the C<HAS_ENDGRENT_R> symbol,
which indicates to the C program that the endgrent_r()
routine is available.

=item C<d_endhent>

From F<d_endhent.U>:

This variable conditionally defines C<HAS_ENDHOSTENT> if endhostent() is
available to close whatever was being used for host queries.

=item C<d_endhostent_r>

From F<d_endhostent_r.U>:

This variable conditionally defines the C<HAS_ENDHOSTENT_R> symbol,
which indicates to the C program that the endhostent_r()
routine is available.

=item C<d_endnent>

From F<d_endnent.U>:

This variable conditionally defines C<HAS_ENDNETENT> if endnetent() is
available to close whatever was being used for network queries.

=item C<d_endnetent_r>

From F<d_endnetent_r.U>:

This variable conditionally defines the C<HAS_ENDNETENT_R> symbol,
which indicates to the C program that the endnetent_r()
routine is available.

=item C<d_endpent>

From F<d_endpent.U>:

This variable conditionally defines C<HAS_ENDPROTOENT> if endprotoent() is
available to close whatever was being used for protocol queries.

=item C<d_endprotoent_r>

From F<d_endprotoent_r.U>:

This variable conditionally defines the C<HAS_ENDPROTOENT_R> symbol,
which indicates to the C program that the endprotoent_r()
routine is available.

=item C<d_endpwent>

From F<d_endpwent.U>:

This variable conditionally defines the C<HAS_ENDPWENT> symbol, which
indicates to the C program that the endpwent() routine is available
for sequential access of the passwd database.

=item C<d_endpwent_r>

From F<d_endpwent_r.U>:

This variable conditionally defines the C<HAS_ENDPWENT_R> symbol,
which indicates to the C program that the endpwent_r()
routine is available.

=item C<d_endsent>

From F<d_endsent.U>:

This variable conditionally defines C<HAS_ENDSERVENT> if endservent() is
available to close whatever was being used for service queries.

=item C<d_endservent_r>

From F<d_endservent_r.U>:

This variable conditionally defines the C<HAS_ENDSERVENT_R> symbol,
which indicates to the C program that the endservent_r()
routine is available.

=item C<d_eofnblk>

From F<nblock_io.U>:

This variable conditionally defines C<EOF_NONBLOCK> if C<EOF> can be seen
when reading from a non-blocking I/O source.

=item C<d_erf>

From F<d_erf.U>:

This variable conditionally defines the C<HAS_ERF> symbol, which
indicates to the C program that the erf() routine is available.

=item C<d_erfc>

From F<d_erfc.U>:

This variable conditionally defines the C<HAS_ERFC> symbol, which
indicates to the C program that the erfc() routine is available.

=item C<d_eunice>

From F<Guess.U>:

This variable conditionally defines the symbols C<EUNICE> and C<VAX>, which
alerts the C program that it must deal with idiosyncrasies of C<VMS>.

=item C<d_exp2>

From F<d_exp2.U>:

This variable conditionally defines the HAS_EXP2 symbol, which
indicates to the C program that the exp2() routine is available.

=item C<d_expm1>

From F<d_expm1.U>:

This variable conditionally defines the HAS_EXPM1 symbol, which
indicates to the C program that the expm1() routine is available.

=item C<d_faststdio>

From F<d_faststdio.U>:

This variable conditionally defines the C<HAS_FAST_STDIO> symbol,
which indicates to the C program that the "fast stdio" is available
to manipulate the stdio buffers directly.

=item C<d_fchdir>

From F<d_fchdir.U>:

This variable conditionally defines the C<HAS_FCHDIR> symbol, which
indicates to the C program that the fchdir() routine is available.

=item C<d_fchmod>

From F<d_fchmod.U>:

This variable conditionally defines the C<HAS_FCHMOD> symbol, which
indicates to the C program that the fchmod() routine is available
to change mode of opened files.

=item C<d_fchmodat>

From F<d_fsat.U>:

This variable conditionally defines the C<HAS_FCHMODAT> symbol, which
indicates the C<POSIX> fchmodat() function is available.

=item C<d_fchown>

From F<d_fchown.U>:

This variable conditionally defines the C<HAS_FCHOWN> symbol, which
indicates to the C program that the fchown() routine is available
to change ownership of opened files.

=item C<d_fcntl>

From F<d_fcntl.U>:

This variable conditionally defines the C<HAS_FCNTL> symbol, and indicates
whether the fcntl() function exists

=item C<d_fcntl_can_lock>

From F<d_fcntl_can_lock.U>:

This variable conditionally defines the C<FCNTL_CAN_LOCK> symbol
and indicates whether file locking with fcntl() works.

=item C<d_fd_macros>

From F<d_fd_set.U>:

This variable contains the eventual value of the C<HAS_FD_MACROS> symbol,
which indicates if your C compiler knows about the macros which
manipulate an fd_set.

=item C<d_fd_set>

From F<d_fd_set.U>:

This variable contains the eventual value of the C<HAS_FD_SET> symbol,
which indicates if your C compiler knows about the fd_set typedef.

=item C<d_fdclose>

From F<d_fdclose.U>:

This variable conditionally defines the C<HAS_FDCLOSE> symbol, which
indicates to the C program that the fdclose() routine is available.

=item C<d_fdim>

From F<d_fdim.U>:

This variable conditionally defines the C<HAS_FDIM> symbol, which
indicates to the C program that the fdim() routine is available.

=item C<d_fds_bits>

From F<d_fd_set.U>:

This variable contains the eventual value of the C<HAS_FDS_BITS> symbol,
which indicates if your fd_set typedef contains the fds_bits member.
If you have an fd_set typedef, but the dweebs who installed it did
a half-fast job and neglected to provide the macros to manipulate
an fd_set, C<HAS_FDS_BITS> will let us know how to fix the gaffe.

=item C<d_fegetround>

From F<d_fegetround.U>:

This variable conditionally defines C<HAS_FEGETROUND> if fegetround() is
available to get the floating point rounding mode.

=item C<d_fgetpos>

From F<d_fgetpos.U>:

This variable conditionally defines C<HAS_FGETPOS> if fgetpos() is
available to get the file position indicator.

=item C<d_finite>

From F<d_finite.U>:

This variable conditionally defines the C<HAS_FINITE> symbol, which
indicates to the C program that the finite() routine is available.

=item C<d_finitel>

From F<d_finitel.U>:

This variable conditionally defines the C<HAS_FINITEL> symbol, which
indicates to the C program that the finitel() routine is available.

=item C<d_flexfnam>

From F<d_flexfnam.U>:

This variable conditionally defines the C<FLEXFILENAMES> symbol, which
indicates that the system supports filenames longer than 14 characters.

=item C<d_flock>

From F<d_flock.U>:

This variable conditionally defines C<HAS_FLOCK> if flock() is
available to do file locking.

=item C<d_flockproto>

From F<d_flockproto.U>:

This variable conditionally defines the C<HAS_FLOCK_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the flock() function. Otherwise, it is
up to the program to supply one.

=item C<d_fma>

From F<d_fma.U>:

This variable conditionally defines the C<HAS_FMA> symbol, which
indicates to the C program that the fma() routine is available.

=item C<d_fmax>

From F<d_fmax.U>:

This variable conditionally defines the C<HAS_FMAX> symbol, which
indicates to the C program that the fmax() routine is available.

=item C<d_fmin>

From F<d_fmin.U>:

This variable conditionally defines the C<HAS_FMIN> symbol, which
indicates to the C program that the fmin() routine is available.

=item C<d_fork>

From F<d_fork.U>:

This variable conditionally defines the C<HAS_FORK> symbol, which
indicates to the C program that the fork() routine is available.

=item C<d_fp_class>

From F<d_fp_class.U>:

This variable conditionally defines the C<HAS_FP_CLASS> symbol, which
indicates to the C program that the fp_class() routine is available.

=item C<d_fp_classify>

From F<d_fpclassify.U>:

This variable conditionally defines the C<HAS_FP_CLASSIFY> symbol, which
indicates to the C program that the fp_classify() routine is available.

=item C<d_fp_classl>

From F<d_fp_classl.U>:

This variable conditionally defines the C<HAS_FP_CLASSL> symbol, which
indicates to the C program that the fp_classl() routine is available.

=item C<d_fpathconf>

From F<d_pathconf.U>:

This variable conditionally defines the C<HAS_FPATHCONF> symbol, which
indicates to the C program that the pathconf() routine is available
to determine file-system related limits and options associated
with a given open file descriptor.

=item C<d_fpclass>

From F<d_fpclass.U>:

This variable conditionally defines the C<HAS_FPCLASS> symbol, which
indicates to the C program that the fpclass() routine is available.

=item C<d_fpclassify>

From F<d_fpclassify.U>:

This variable conditionally defines the C<HAS_FPCLASSIFY> symbol, which
indicates to the C program that the fpclassify() routine is available.

=item C<d_fpclassl>

From F<d_fpclassl.U>:

This variable conditionally defines the C<HAS_FPCLASSL> symbol, which
indicates to the C program that the fpclassl() routine is available.

=item C<d_fpgetround>

From F<d_fpgetround.U>:

This variable conditionally defines C<HAS_FPGETROUND> if fpgetround()
is available to get the floating point rounding mode.

=item C<d_fpos64_t>

From F<d_fpos64_t.U>:

This symbol will be defined if the C compiler supports fpos64_t.

=item C<d_freelocale>

From F<d_newlocale.U>:

This variable conditionally defines the C<HAS_FREELOCALE> symbol, which
indicates to the C program that the freelocale() routine is available
to deallocates the resources associated with a locale object.

=item C<d_frexpl>

From F<d_frexpl.U>:

This variable conditionally defines the C<HAS_FREXPL> symbol, which
indicates to the C program that the frexpl() routine is available.

=item C<d_fs_data_s>

From F<d_fs_data_s.U>:

This variable conditionally defines the C<HAS_STRUCT_FS_DATA> symbol,
which indicates that the struct fs_data is supported.

=item C<d_fseeko>

From F<d_fseeko.U>:

This variable conditionally defines the C<HAS_FSEEKO> symbol, which
indicates to the C program that the fseeko() routine is available.

=item C<d_fsetpos>

From F<d_fsetpos.U>:

This variable conditionally defines C<HAS_FSETPOS> if fsetpos() is
available to set the file position indicator.

=item C<d_fstatfs>

From F<d_fstatfs.U>:

This variable conditionally defines the C<HAS_FSTATFS> symbol, which
indicates to the C program that the fstatfs() routine is available.

=item C<d_fstatvfs>

From F<d_statvfs.U>:

This variable conditionally defines the C<HAS_FSTATVFS> symbol, which
indicates to the C program that the fstatvfs() routine is available.

=item C<d_fsync>

From F<d_fsync.U>:

This variable conditionally defines the C<HAS_FSYNC> symbol, which
indicates to the C program that the fsync() routine is available.

=item C<d_ftello>

From F<d_ftello.U>:

This variable conditionally defines the C<HAS_FTELLO> symbol, which
indicates to the C program that the ftello() routine is available.

=item C<d_ftime>

From F<d_ftime.U>:

This variable conditionally defines the C<HAS_FTIME> symbol, which indicates
that the ftime() routine exists. The ftime() routine is basically
a sub-second accuracy clock.

=item C<d_futimes>

From F<d_futimes.U>:

This variable conditionally defines the C<HAS_FUTIMES> symbol, which
indicates to the C program that the futimes() routine is available.

=item C<d_gai_strerror>

From F<d_gai_strerror.U>:

This variable conditionally defines the C<HAS_GAI_STRERROR> symbol
if the gai_strerror() routine is available and can be used to
translate error codes returned by getaddrinfo() into human
readable strings.

=item C<d_Gconvert>

From F<d_gconvert.U>:

This variable holds what Gconvert is defined as to convert
floating point numbers into strings. By default, Configure
sets C<this> macro to use the first of gconvert, gcvt, or sprintf
that pass sprintf-%g-like behavior tests. If perl is using
long doubles, the macro uses the first of the following
functions that pass Configure's tests: qgcvt, sprintf (if
Configure knows how to make sprintf format long doubles--see
sPRIgldbl), gconvert, gcvt, and sprintf (casting to double).
The gconvert_preference and gconvert_ld_preference variables
can be used to alter Configure's preferences, for doubles and
long doubles, respectively. If present, they contain a
space-separated list of one or more of the above function
names in the order they should be tried.

d_Gconvert may be set to override Configure with a platform-
specific function. If this function expects a double, a
different value may need to be set by the F<uselongdouble.cbu>
call-back unit so that long doubles can be formatted without
loss of precision.

=item C<d_gdbm_ndbm_h_uses_prototypes>

From F<i_ndbm.U>:

This variable conditionally defines the C<NDBM_H_USES_PROTOTYPES> symbol,
which indicates that the gdbm-F<ndbm.h> include file uses real C<ANSI> C
prototypes instead of K&R style function declarations. K&R style
declarations are unsupported in C++, so the include file requires
special handling when using a C++ compiler and this variable is
undefined. Consult the different d_*ndbm_h_uses_prototypes variables
to get the same information for alternative F<ndbm.h> include files.

=item C<d_gdbmndbm_h_uses_prototypes>

From F<i_ndbm.U>:

This variable conditionally defines the C<NDBM_H_USES_PROTOTYPES> symbol,
which indicates that the F<gdbm/ndbm.h> include file uses real C<ANSI> C
prototypes instead of K&R style function declarations. K&R style
declarations are unsupported in C++, so the include file requires
special handling when using a C++ compiler and this variable is
undefined. Consult the different d_*ndbm_h_uses_prototypes variables
to get the same information for alternative F<ndbm.h> include files.

=item C<d_getaddrinfo>

From F<d_getaddrinfo.U>:

This variable conditionally defines the C<HAS_GETADDRINFO> symbol,
which indicates to the C program that the getaddrinfo() function
is available.

=item C<d_getcwd>

From F<d_getcwd.U>:

This variable conditionally defines the C<HAS_GETCWD> symbol, which
indicates to the C program that the getcwd() routine is available
to get the current working directory.

=item C<d_getespwnam>

From F<d_getespwnam.U>:

This variable conditionally defines C<HAS_GETESPWNAM> if getespwnam() is
available to retrieve enhanced (shadow) password entries by name.

=item C<d_getfsstat>

From F<d_getfsstat.U>:

This variable conditionally defines the C<HAS_GETFSSTAT> symbol, which
indicates to the C program that the getfsstat() routine is available.

=item C<d_getgrent>

From F<d_getgrent.U>:

This variable conditionally defines the C<HAS_GETGRENT> symbol, which
indicates to the C program that the getgrent() routine is available
for sequential access of the group database.

=item C<d_getgrent_r>

From F<d_getgrent_r.U>:

This variable conditionally defines the C<HAS_GETGRENT_R> symbol,
which indicates to the C program that the getgrent_r()
routine is available.

=item C<d_getgrgid_r>

From F<d_getgrgid_r.U>:

This variable conditionally defines the C<HAS_GETGRGID_R> symbol,
which indicates to the C program that the getgrgid_r()
routine is available.

=item C<d_getgrnam_r>

From F<d_getgrnam_r.U>:

This variable conditionally defines the C<HAS_GETGRNAM_R> symbol,
which indicates to the C program that the getgrnam_r()
routine is available.

=item C<d_getgrps>

From F<d_getgrps.U>:

This variable conditionally defines the C<HAS_GETGROUPS> symbol, which
indicates to the C program that the getgroups() routine is available
to get the list of process groups.

=item C<d_gethbyaddr>

From F<d_gethbyad.U>:

This variable conditionally defines the C<HAS_GETHOSTBYADDR> symbol, which
indicates to the C program that the gethostbyaddr() routine is available
to look up hosts by their C<IP> addresses.

=item C<d_gethbyname>

From F<d_gethbynm.U>:

This variable conditionally defines the C<HAS_GETHOSTBYNAME> symbol, which
indicates to the C program that the gethostbyname() routine is available
to look up host names in some data base or other.

=item C<d_gethent>

From F<d_gethent.U>:

This variable conditionally defines C<HAS_GETHOSTENT> if gethostent() is
available to look up host names in some data base or another.

=item C<d_gethname>

From F<d_gethname.U>:

This variable conditionally defines the C<HAS_GETHOSTNAME> symbol, which
indicates to the C program that the gethostname() routine may be
used to derive the host name.

=item C<d_gethostbyaddr_r>

From F<d_gethostbyaddr_r.U>:

This variable conditionally defines the C<HAS_GETHOSTBYADDR_R> symbol,
which indicates to the C program that the gethostbyaddr_r()
routine is available.

=item C<d_gethostbyname_r>

From F<d_gethostbyname_r.U>:

This variable conditionally defines the C<HAS_GETHOSTBYNAME_R> symbol,
which indicates to the C program that the gethostbyname_r()
routine is available.

=item C<d_gethostent_r>

From F<d_gethostent_r.U>:

This variable conditionally defines the C<HAS_GETHOSTENT_R> symbol,
which indicates to the C program that the gethostent_r()
routine is available.

=item C<d_gethostprotos>

From F<d_gethostprotos.U>:

This variable conditionally defines the C<HAS_GETHOST_PROTOS> symbol,
which indicates to the C program that <netdb.h> supplies
prototypes for the various gethost*() functions.
See also F<netdbtype.U> for probing for various netdb types.

=item C<d_getitimer>

From F<d_getitimer.U>:

This variable conditionally defines the C<HAS_GETITIMER> symbol, which
indicates to the C program that the getitimer() routine is available.

=item C<d_getlogin>

From F<d_getlogin.U>:

This variable conditionally defines the C<HAS_GETLOGIN> symbol, which
indicates to the C program that the getlogin() routine is available
to get the login name.

=item C<d_getlogin_r>

From F<d_getlogin_r.U>:

This variable conditionally defines the C<HAS_GETLOGIN_R> symbol,
which indicates to the C program that the getlogin_r()
routine is available.

=item C<d_getmnt>

From F<d_getmnt.U>:

This variable conditionally defines the C<HAS_GETMNT> symbol, which
indicates to the C program that the getmnt() routine is available
to retrieve one or more mount info blocks by filename.

=item C<d_getmntent>

From F<d_getmntent.U>:

This variable conditionally defines the C<HAS_GETMNTENT> symbol, which
indicates to the C program that the getmntent() routine is available
to iterate through mounted files to get their mount info.

=item C<d_getnameinfo>

From F<d_getnameinfo.U>:

This variable conditionally defines the C<HAS_GETNAMEINFO> symbol,
which indicates to the C program that the getnameinfo() function
is available.

=item C<d_getnbyaddr>

From F<d_getnbyad.U>:

This variable conditionally defines the C<HAS_GETNETBYADDR> symbol, which
indicates to the C program that the getnetbyaddr() routine is available
to look up networks by their C<IP> addresses.

=item C<d_getnbyname>

From F<d_getnbynm.U>:

This variable conditionally defines the C<HAS_GETNETBYNAME> symbol, which
indicates to the C program that the getnetbyname() routine is available
to look up networks by their names.

=item C<d_getnent>

From F<d_getnent.U>:

This variable conditionally defines C<HAS_GETNETENT> if getnetent() is
available to look up network names in some data base or another.

=item C<d_getnetbyaddr_r>

From F<d_getnetbyaddr_r.U>:

This variable conditionally defines the C<HAS_GETNETBYADDR_R> symbol,
which indicates to the C program that the getnetbyaddr_r()
routine is available.

=item C<d_getnetbyname_r>

From F<d_getnetbyname_r.U>:

This variable conditionally defines the C<HAS_GETNETBYNAME_R> symbol,
which indicates to the C program that the getnetbyname_r()
routine is available.

=item C<d_getnetent_r>

From F<d_getnetent_r.U>:

This variable conditionally defines the C<HAS_GETNETENT_R> symbol,
which indicates to the C program that the getnetent_r()
routine is available.

=item C<d_getnetprotos>

From F<d_getnetprotos.U>:

This variable conditionally defines the C<HAS_GETNET_PROTOS> symbol,
which indicates to the C program that <netdb.h> supplies
prototypes for the various getnet*() functions.
See also F<netdbtype.U> for probing for various netdb types.

=item C<d_getpagsz>

From F<d_getpagsz.U>:

This variable conditionally defines C<HAS_GETPAGESIZE> if getpagesize()
is available to get the system page size.

=item C<d_getpbyname>

From F<d_getprotby.U>:

This variable conditionally defines the C<HAS_GETPROTOBYNAME>
symbol, which indicates to the C program that the
getprotobyname() routine is available to look up protocols
by their name.

=item C<d_getpbynumber>

From F<d_getprotby.U>:

This variable conditionally defines the C<HAS_GETPROTOBYNUMBER>
symbol, which indicates to the C program that the
getprotobynumber() routine is available to look up protocols
by their number.

=item C<d_getpent>

From F<d_getpent.U>:

This variable conditionally defines C<HAS_GETPROTOENT> if getprotoent() is
available to look up protocols in some data base or another.

=item C<d_getpgid>

From F<d_getpgid.U>:

This variable conditionally defines the C<HAS_GETPGID> symbol, which
indicates to the C program that the getpgid(pid) function
is available to get the process group id.

=item C<d_getpgrp>

From F<d_getpgrp.U>:

This variable conditionally defines C<HAS_GETPGRP> if getpgrp() is
available to get the current process group.

=item C<d_getpgrp2>

From F<d_getpgrp2.U>:

This variable conditionally defines the HAS_GETPGRP2 symbol, which
indicates to the C program that the getpgrp2() (as in F<DG/C<UX>>) routine
is available to get the current process group.

=item C<d_getppid>

From F<d_getppid.U>:

This variable conditionally defines the C<HAS_GETPPID> symbol, which
indicates to the C program that the getppid() routine is available
to get the parent process C<ID>.

=item C<d_getprior>

From F<d_getprior.U>:

This variable conditionally defines C<HAS_GETPRIORITY> if getpriority()
is available to get a process's priority.

=item C<d_getprotobyname_r>

From F<d_getprotobyname_r.U>:

This variable conditionally defines the C<HAS_GETPROTOBYNAME_R> symbol,
which indicates to the C program that the getprotobyname_r()
routine is available.

=item C<d_getprotobynumber_r>

From F<d_getprotobynumber_r.U>:

This variable conditionally defines the C<HAS_GETPROTOBYNUMBER_R> symbol,
which indicates to the C program that the getprotobynumber_r()
routine is available.

=item C<d_getprotoent_r>

From F<d_getprotoent_r.U>:

This variable conditionally defines the C<HAS_GETPROTOENT_R> symbol,
which indicates to the C program that the getprotoent_r()
routine is available.

=item C<d_getprotoprotos>

From F<d_getprotoprotos.U>:

This variable conditionally defines the C<HAS_GETPROTO_PROTOS> symbol,
which indicates to the C program that <netdb.h> supplies
prototypes for the various getproto*() functions.
See also F<netdbtype.U> for probing for various netdb types.

=item C<d_getprpwnam>

From F<d_getprpwnam.U>:

This variable conditionally defines C<HAS_GETPRPWNAM> if getprpwnam() is
available to retrieve protected (shadow) password entries by name.

=item C<d_getpwent>

From F<d_getpwent.U>:

This variable conditionally defines the C<HAS_GETPWENT> symbol, which
indicates to the C program that the getpwent() routine is available
for sequential access of the passwd database.

=item C<d_getpwent_r>

From F<d_getpwent_r.U>:

This variable conditionally defines the C<HAS_GETPWENT_R> symbol,
which indicates to the C program that the getpwent_r()
routine is available.

=item C<d_getpwnam_r>

From F<d_getpwnam_r.U>:

This variable conditionally defines the C<HAS_GETPWNAM_R> symbol,
which indicates to the C program that the getpwnam_r()
routine is available.

=item C<d_getpwuid_r>

From F<d_getpwuid_r.U>:

This variable conditionally defines the C<HAS_GETPWUID_R> symbol,
which indicates to the C program that the getpwuid_r()
routine is available.

=item C<d_getsbyname>

From F<d_getsrvby.U>:

This variable conditionally defines the C<HAS_GETSERVBYNAME>
symbol, which indicates to the C program that the
getservbyname() routine is available to look up services
by their name.

=item C<d_getsbyport>

From F<d_getsrvby.U>:

This variable conditionally defines the C<HAS_GETSERVBYPORT>
symbol, which indicates to the C program that the
getservbyport() routine is available to look up services
by their port.

=item C<d_getsent>

From F<d_getsent.U>:

This variable conditionally defines C<HAS_GETSERVENT> if getservent() is
available to look up network services in some data base or another.

=item C<d_getservbyname_r>

From F<d_getservbyname_r.U>:

This variable conditionally defines the C<HAS_GETSERVBYNAME_R> symbol,
which indicates to the C program that the getservbyname_r()
routine is available.

=item C<d_getservbyport_r>

From F<d_getservbyport_r.U>:

This variable conditionally defines the C<HAS_GETSERVBYPORT_R> symbol,
which indicates to the C program that the getservbyport_r()
routine is available.

=item C<d_getservent_r>

From F<d_getservent_r.U>:

This variable conditionally defines the C<HAS_GETSERVENT_R> symbol,
which indicates to the C program that the getservent_r()
routine is available.

=item C<d_getservprotos>

From F<d_getservprotos.U>:

This variable conditionally defines the C<HAS_GETSERV_PROTOS> symbol,
which indicates to the C program that <netdb.h> supplies
prototypes for the various getserv*() functions.
See also F<netdbtype.U> for probing for various netdb types.

=item C<d_getspnam>

From F<d_getspnam.U>:

This variable conditionally defines C<HAS_GETSPNAM> if getspnam() is
available to retrieve SysV shadow password entries by name.

=item C<d_getspnam_r>

From F<d_getspnam_r.U>:

This variable conditionally defines the C<HAS_GETSPNAM_R> symbol,
which indicates to the C program that the getspnam_r()
routine is available.

=item C<d_gettimeod>

From F<d_ftime.U>:

This variable conditionally defines the C<HAS_GETTIMEOFDAY> symbol, which
indicates that the gettimeofday() system call exists (to obtain a
sub-second accuracy clock). You should probably include <sys/resource.h>.

=item C<d_gmtime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_GMTIME64 symbol, which
indicates to the C program that the gmtime64 () routine is available.

=item C<d_gmtime_r>

From F<d_gmtime_r.U>:

This variable conditionally defines the C<HAS_GMTIME_R> symbol,
which indicates to the C program that the gmtime_r()
routine is available.

=item C<d_gnulibc>

From F<d_gnulibc.U>:

Defined if we're dealing with the C<GNU> C Library.

=item C<d_grpasswd>

From F<i_grp.U>:

This variable conditionally defines C<GRPASSWD>, which indicates
that struct group in <grp.h> contains gr_passwd.

=item C<d_has_C_UTF8>

From F<d_setlocale.U>:

This variable is set to either C<true> or C<false> depending on
whether the compilation system supports the F<C.UTF>-8 locale.

=item C<d_hasmntopt>

From F<d_hasmntopt.U>:

This variable conditionally defines the C<HAS_HASMNTOPT> symbol, which
indicates to the C program that the hasmntopt() routine is available
to query the mount options of file systems.

=item C<d_htonl>

From F<d_htonl.U>:

This variable conditionally defines C<HAS_HTONL> if htonl() and its
friends are available to do network order byte swapping.

=item C<d_hypot>

From F<d_hypot.U>:

This variable conditionally defines C<HAS_HYPOT> if hypot is available
for numerically stable hypotenuse function.

=item C<d_ilogb>

From F<d_ilogb.U>:

This variable conditionally defines the C<HAS_ILOGB> symbol, which
indicates to the C program that the ilogb() routine is available
for extracting the exponent of double x as a signed integer.

=item C<d_ilogbl>

From F<d_ilogbl.U>:

This variable conditionally defines the C<HAS_ILOGBL> symbol, which
indicates to the C program that the ilogbl() routine is available
for extracting the exponent of long double x as a signed integer.
If scalbnl is also present we can emulate frexpl.

=item C<d_inc_version_list>

From F<inc_version_list.U>:

This variable conditionally defines C<PERL_INC_VERSION_LIST>.
It is set to undef when C<PERL_INC_VERSION_LIST> is empty.

=item C<d_inetaton>

From F<d_inetaton.U>:

This variable conditionally defines the C<HAS_INET_ATON> symbol, which
indicates to the C program that the inet_aton() function is available
to parse C<IP> address C<dotted-quad> strings.

=item C<d_inetntop>

From F<d_inetntop.U>:

This variable conditionally defines the C<HAS_INETNTOP> symbol,
which indicates to the C program that the inet_ntop() function
is available.

=item C<d_inetpton>

From F<d_inetpton.U>:

This variable conditionally defines the C<HAS_INETPTON> symbol,
which indicates to the C program that the inet_pton() function
is available.

=item C<d_int64_t>

From F<d_int64_t.U>:

This symbol will be defined if the C compiler supports int64_t.

=item C<d_ip_mreq>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_IP_MREQ> symbol, which
indicates the availability of a struct ip_mreq.

=item C<d_ip_mreq_source>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_IP_MREQ_SOURCE> symbol,
which indicates the availability of a struct ip_mreq_source.

=item C<d_ipv6_mreq>

From F<d_socket.U>:

This variable conditionally defines the HAS_IPV6_MREQ symbol, which
indicates the availability of a struct ipv6_mreq.

=item C<d_ipv6_mreq_source>

From F<d_socket.U>:

This variable conditionally defines the HAS_IPV6_MREQ_SOURCE symbol,
which indicates the availability of a struct ipv6_mreq_source.

=item C<d_isascii>

From F<d_isascii.U>:

This variable conditionally defines the C<HAS_ISASCII> constant,
which indicates to the C program that isascii() is available.

=item C<d_isblank>

From F<d_isblank.U>:

This variable conditionally defines the C<HAS_ISBLANK> constant,
which indicates to the C program that isblank() is available.

=item C<d_isfinite>

From F<d_isfinite.U>:

This variable conditionally defines the C<HAS_ISFINITE> symbol, which
indicates to the C program that the isfinite() routine is available.

=item C<d_isfinitel>

From F<d_isfinitel.U>:

This variable conditionally defines the C<HAS_ISFINITEL> symbol, which
indicates to the C program that the isfinitel() routine is available.

=item C<d_isinf>

From F<d_isinf.U>:

This variable conditionally defines the C<HAS_ISINF> symbol, which
indicates to the C program that the isinf() routine is available.

=item C<d_isinfl>

From F<d_isinfl.U>:

This variable conditionally defines the C<HAS_ISINFL> symbol, which
indicates to the C program that the isinfl() routine is available.

=item C<d_isless>

From F<d_isless.U>:

This variable conditionally defines the C<HAS_ISLESS> symbol, which
indicates to the C program that the isless() routine is available.

=item C<d_isnan>

From F<d_isnan.U>:

This variable conditionally defines the C<HAS_ISNAN> symbol, which
indicates to the C program that the isnan() routine is available.

=item C<d_isnanl>

From F<d_isnanl.U>:

This variable conditionally defines the C<HAS_ISNANL> symbol, which
indicates to the C program that the isnanl() routine is available.

=item C<d_isnormal>

From F<d_isnormal.U>:

This variable conditionally defines the C<HAS_ISNORMAL> symbol, which
indicates to the C program that the isnormal() routine is available.

=item C<d_j0>

From F<d_j0.U>:

This variable conditionally defines the HAS_J0 symbol, which
indicates to the C program that the j0() routine is available.

=item C<d_j0l>

From F<d_j0.U>:

This variable conditionally defines the HAS_J0L symbol, which
indicates to the C program that the j0l() routine is available.

=item C<d_killpg>

From F<d_killpg.U>:

This variable conditionally defines the C<HAS_KILLPG> symbol, which
indicates to the C program that the killpg() routine is available
to kill process groups.

=item C<d_lc_monetary_2008>

From F<d_lc_monetary_2008.U>:

This variable conditionally defines HAS_LC_MONETARY_2008 if libc
has the international currency locale rules from C<POSIX>
1003.1-2008.

=item C<d_lchown>

From F<d_lchown.U>:

This variable conditionally defines the C<HAS_LCHOWN> symbol, which
indicates to the C program that the lchown() routine is available
to operate on a symbolic link (instead of following the link).

=item C<d_ldbl_dig>

From F<d_ldbl_dig.U>:

This variable conditionally defines d_ldbl_dig if this system's
header files provide C<LDBL_DIG>, which is the number of significant
digits in a long double precision number.

=item C<d_ldexpl>

From F<d_longdbl.U>:

This variable conditionally defines the C<HAS_LDEXPL> symbol, which
indicates to the C program that the ldexpl() routine is available.

=item C<d_lgamma>

From F<d_lgamma.U>:

This variable conditionally defines the C<HAS_LGAMMA> symbol, which
indicates to the C program that the lgamma() routine is available
for the log gamma function. See also d_tgamma and d_lgamma_r.

=item C<d_lgamma_r>

From F<d_lgamma_r.U>:

This variable conditionally defines the C<HAS_LGAMMA_R> symbol, which
indicates to the C program that the lgamma_r() routine is available
for the log gamma function, without using the global signgam variable.

=item C<d_libm_lib_version>

From F<d_libm_lib_version.U>:

This variable conditionally defines the C<LIBM_LIB_VERSION> symbol,
which indicates to the C program that F<math.h> defines C<_LIB_VERSION>
being available in libm

=item C<d_libname_unique>

From F<so.U>:

This variable is defined if the target system insists on unique
basenames for shared library files. This is currently true on Android,
false everywhere else we know of.
Defaults to C<undef>.

=item C<d_link>

From F<d_link.U>:

This variable conditionally defines C<HAS_LINK> if link() is
available to create hard links.

=item C<d_linkat>

From F<d_fsat.U>:

This variable conditionally defines the C<HAS_LINKAT> symbol, which
indicates the C<POSIX> linkat() function is available.

=item C<d_llrint>

From F<d_llrint.U>:

This variable conditionally defines the C<HAS_LLRINT> symbol, which
indicates to the C program that the llrint() routine is available
to return the long long value closest to a double (according
to the current rounding mode).

=item C<d_llrintl>

From F<d_llrintl.U>:

This variable conditionally defines the C<HAS_LLRINTL> symbol, which
indicates to the C program that the llrintl() routine is available
to return the long long value closest to a long double (according
to the current rounding mode).

=item C<d_llround>

From F<d_llround.U>:

This variable conditionally defines the C<HAS_LLROUND> symbol, which
indicates to the C program that the llround() routine is available
to return the long long value nearest to x.

=item C<d_llroundl>

From F<d_llroundl.U>:

This variable conditionally defines the C<HAS_LLROUNDL> symbol, which
indicates to the C program that the llroundl() routine is available
to return the long long value nearest to x away from zero.

=item C<d_localeconv_l>

From F<d_localeconv_l.U>:

This variable conditionally defines the C<HAS_LOCALECONV_L> symbol, which
indicates to the C program that the localeconv_l() routine is available.

=item C<d_localtime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_LOCALTIME64 symbol, which
indicates to the C program that the localtime64 () routine is available.

=item C<d_localtime_r>

From F<d_localtime_r.U>:

This variable conditionally defines the C<HAS_LOCALTIME_R> symbol,
which indicates to the C program that the localtime_r()
routine is available.

=item C<d_localtime_r_needs_tzset>

From F<d_localtime_r.U>:

This variable conditionally defines the C<LOCALTIME_R_NEEDS_TZSET>
symbol, which makes us call tzset before localtime_r()

=item C<d_locconv>

From F<d_locconv.U>:

This variable conditionally defines C<HAS_LOCALECONV> if localeconv() is
available for numeric and monetary formatting conventions.

=item C<d_lockf>

From F<d_lockf.U>:

This variable conditionally defines C<HAS_LOCKF> if lockf() is
available to do file locking.

=item C<d_log1p>

From F<d_log1p.U>:

This variable conditionally defines the HAS_LOG1P symbol, which
indicates to the C program that the logp1() routine is available
to compute log(1 + x) for values of x close to zero.

=item C<d_log2>

From F<d_log2.U>:

This variable conditionally defines the HAS_LOG2 symbol, which
indicates to the C program that the log2() routine is available
to compute log base two.

=item C<d_logb>

From F<d_logb.U>:

This variable conditionally defines the C<HAS_LOGB> symbol, which
indicates to the C program that the logb() routine is available
to extract the exponent of x.

=item C<d_long_double_style_ieee>

From F<d_longdbl.U>:

This variable conditionally defines C<LONG_DOUBLE_STYLE_IEEE>
if the long double is any of the C<IEEE> 754 style long doubles:
C<LONG_DOUBLE_STYLE_IEEE_STD>, C<LONG_DOUBLE_STYLE_IEEE_EXTENDED>,
C<LONG_DOUBLE_STYLE_IEEE_DOUBLEDOUBLE>.

=item C<d_long_double_style_ieee_doubledouble>

From F<d_longdbl.U>:

This variable conditionally defines C<LONG_DOUBLE_STYLE_IEEE_DOUBLEDOUBLE>
if the long double is the 128-bit C<IEEE> 754 double-double.

=item C<d_long_double_style_ieee_extended>

From F<d_longdbl.U>:

This variable conditionally defines C<LONG_DOUBLE_STYLE_IEEE_EXTENDED>
if the long double is the 80-bit C<IEEE> 754 extended precision.
Note that despite the C<extended> this is less than the C<std>,
since thisis an extension of the double precision.

=item C<d_long_double_style_ieee_std>

From F<d_longdbl.U>:

This variable conditionally defines C<LONG_DOUBLE_STYLE_IEEE_STD>
if the long double is the 128-bit C<IEEE> 754.

=item C<d_long_double_style_vax>

From F<d_longdbl.U>:

This variable conditionally defines C<LONG_DOUBLE_STYLE_VAX>
if the long double is the 128-bit C<VAX> format H.

=item C<d_longdbl>

From F<d_longdbl.U>:

This variable conditionally defines C<HAS_LONG_DOUBLE> if
the long double type is supported.

=item C<d_longlong>

From F<d_longlong.U>:

This variable conditionally defines C<HAS_LONG_LONG> if
the long long type is supported.

=item C<d_lrint>

From F<d_lrint.U>:

This variable conditionally defines the C<HAS_LRINT> symbol, which
indicates to the C program that the lrint() routine is available
to return the integral value closest to a double (according
to the current rounding mode).

=item C<d_lrintl>

From F<d_lrintl.U>:

This variable conditionally defines the C<HAS_LRINTL> symbol, which
indicates to the C program that the lrintl() routine is available
to return the integral value closest to a long double (according
to the current rounding mode).

=item C<d_lround>

From F<d_lround.U>:

This variable conditionally defines the C<HAS_LROUND> symbol, which
indicates to the C program that the lround() routine is available
to return the integral value nearest to x.

=item C<d_lroundl>

From F<d_lroundl.U>:

This variable conditionally defines the C<HAS_LROUNDL> symbol, which
indicates to the C program that the lroundl() routine is available
to return the integral value nearest to x away from zero.

=item C<d_lseekproto>

From F<d_lseekproto.U>:

This variable conditionally defines the C<HAS_LSEEK_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the lseek() function. Otherwise, it is
up to the program to supply one.

=item C<d_lstat>

From F<d_lstat.U>:

This variable conditionally defines C<HAS_LSTAT> if lstat() is
available to do file stats on symbolic links.

=item C<d_madvise>

From F<d_madvise.U>:

This variable conditionally defines C<HAS_MADVISE> if madvise() is
available to map a file into memory.

=item C<d_malloc_good_size>

From F<d_malloc_size.U>:

This symbol, if defined, indicates that the malloc_good_size
routine is available for use.

=item C<d_malloc_size>

From F<d_malloc_size.U>:

This symbol, if defined, indicates that the malloc_size
routine is available for use.

=item C<d_mblen>

From F<d_mblen.U>:

This variable conditionally defines the C<HAS_MBLEN> symbol, which
indicates to the C program that the mblen() routine is available
to find the number of bytes in a multibye character.

=item C<d_mbrlen>

From F<d_mbrlen.U>:

This variable conditionally defines the C<HAS_MBRLEN> symbol if the
mbrlen() routine is available to be used to get the length of
multi-byte character strings.

=item C<d_mbrtowc>

From F<d_mbrtowc.U>:

This variable conditionally defines the C<HAS_MBRTOWC> symbol if the
mbrtowc() routine is available to be used to convert a multi-byte
character into a wide character.

=item C<d_mbstowcs>

From F<d_mbstowcs.U>:

This variable conditionally defines the C<HAS_MBSTOWCS> symbol, which
indicates to the C program that the mbstowcs() routine is available
to convert a multibyte string into a wide character string.

=item C<d_mbtowc>

From F<d_mbtowc.U>:

This variable conditionally defines the C<HAS_MBTOWC> symbol, which
indicates to the C program that the mbtowc() routine is available
to convert multibyte to a wide character.

=item C<d_memmem>

From F<d_memmem.U>:

This variable conditionally defines the C<HAS_MEMMEM> symbol, which
indicates to the C program that the memmem() routine is available
to return a pointer to the start of the first occurance of a
substring in a memory area (or C<NULL> if not found).

=item C<d_memrchr>

From F<d_memrchr.U>:

This variable conditionally defines the C<HAS_MEMRCHR> symbol, which
indicates to the C program that the memrchr() routine is available
to return a pointer to the last occurrence of a byte in a memory
area (or C<NULL> if not found).

=item C<d_mkdir>

From F<d_mkdir.U>:

This variable conditionally defines the C<HAS_MKDIR> symbol, which
indicates to the C program that the mkdir() routine is available
to create F<directories.>.

=item C<d_mkdtemp>

From F<d_mkdtemp.U>:

This variable conditionally defines the C<HAS_MKDTEMP> symbol, which
indicates to the C program that the mkdtemp() routine is available
to exclusively create a uniquely named temporary directory.

=item C<d_mkfifo>

From F<d_mkfifo.U>:

This variable conditionally defines the C<HAS_MKFIFO> symbol, which
indicates to the C program that the mkfifo() routine is available.

=item C<d_mkostemp>

From F<d_mkostemp.U>:

This variable conditionally defines C<HAS_MKOSTEMP> if mkostemp() is
available to exclusively create and open a uniquely named (with a
suffix) temporary file.

=item C<d_mkstemp>

From F<d_mkstemp.U>:

This variable conditionally defines the C<HAS_MKSTEMP> symbol, which
indicates to the C program that the mkstemp() routine is available
to exclusively create and open a uniquely named temporary file.

=item C<d_mkstemps>

From F<d_mkstemps.U>:

This variable conditionally defines the C<HAS_MKSTEMPS> symbol, which
indicates to the C program that the mkstemps() routine is available
to exclusively create and open a uniquely named (with a suffix)
temporary file.

=item C<d_mktime>

From F<d_mktime.U>:

This variable conditionally defines the C<HAS_MKTIME> symbol, which
indicates to the C program that the mktime() routine is available.

=item C<d_mktime64>

From F<d_timefuncs64.U>:

This variable conditionally defines the HAS_MKTIME64 symbol, which
indicates to the C program that the mktime64 () routine is available.

=item C<d_mmap>

From F<d_mmap.U>:

This variable conditionally defines C<HAS_MMAP> if mmap() is
available to map a file into memory.

=item C<d_modfl>

From F<d_modfl.U>:

This variable conditionally defines the C<HAS_MODFL> symbol, which
indicates to the C program that the modfl() routine is available.

=item C<d_modflproto>

From F<d_modfl.U>:

This symbol, if defined, indicates that the system provides
a prototype for the modfl() function.  Otherwise, it is up
to the program to supply one.  C99 says it should be
long double modfl(long double, long double *);

=item C<d_mprotect>

From F<d_mprotect.U>:

This variable conditionally defines C<HAS_MPROTECT> if mprotect() is
available to modify the access protection of a memory mapped file.

=item C<d_msg>

From F<d_msg.U>:

This variable conditionally defines the C<HAS_MSG> symbol, which
indicates that the entire msg*(2) library is present.

=item C<d_msg_ctrunc>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_MSG_CTRUNC> symbol,
which indicates that the C<MSG_CTRUNC> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_msg_dontroute>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_MSG_DONTROUTE> symbol,
which indicates that the C<MSG_DONTROUTE> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_msg_oob>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_MSG_OOB> symbol,
which indicates that the C<MSG_OOB> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_msg_peek>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_MSG_PEEK> symbol,
which indicates that the C<MSG_PEEK> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_msg_proxy>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_MSG_PROXY> symbol,
which indicates that the C<MSG_PROXY> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_msgctl>

From F<d_msgctl.U>:

This variable conditionally defines the C<HAS_MSGCTL> symbol, which
indicates to the C program that the msgctl() routine is available.

=item C<d_msgget>

From F<d_msgget.U>:

This variable conditionally defines the C<HAS_MSGGET> symbol, which
indicates to the C program that the msgget() routine is available.

=item C<d_msghdr_s>

From F<d_msghdr_s.U>:

This variable conditionally defines the C<HAS_STRUCT_MSGHDR> symbol,
which indicates that the struct msghdr is supported.

=item C<d_msgrcv>

From F<d_msgrcv.U>:

This variable conditionally defines the C<HAS_MSGRCV> symbol, which
indicates to the C program that the msgrcv() routine is available.

=item C<d_msgsnd>

From F<d_msgsnd.U>:

This variable conditionally defines the C<HAS_MSGSND> symbol, which
indicates to the C program that the msgsnd() routine is available.

=item C<d_msync>

From F<d_msync.U>:

This variable conditionally defines C<HAS_MSYNC> if msync() is
available to synchronize a mapped file.

=item C<d_munmap>

From F<d_munmap.U>:

This variable conditionally defines C<HAS_MUNMAP> if munmap() is
available to unmap a region mapped by mmap().

=item C<d_mymalloc>

From F<mallocsrc.U>:

This variable conditionally defines C<MYMALLOC> in case other parts
of the source want to take special action if C<MYMALLOC> is used.
This may include different sorts of profiling or error detection.

=item C<d_nan>

From F<d_nan.U>:

This variable conditionally defines C<HAS_NAN> if nan() is
available to generate NaN.

=item C<d_nanosleep>

From F<d_nanosleep.U>:

This variable conditionally defines C<HAS_NANOSLEEP>
if nanosleep() is available to sleep with 1E-9 sec accuracy.

=item C<d_ndbm>

From F<i_ndbm.U>:

This variable conditionally defines the C<HAS_NDBM> symbol, which
indicates that both the F<ndbm.h> include file and an appropriate ndbm
library exist. Consult the different i_*ndbm variables
to find out the actual include location. Sometimes, a system has the
header file but not the library. This variable will only be set if
the system has both.

=item C<d_ndbm_h_uses_prototypes>

From F<i_ndbm.U>:

This variable conditionally defines the C<NDBM_H_USES_PROTOTYPES> symbol,
which indicates that the F<ndbm.h> include file uses real C<ANSI> C
prototypes instead of K&R style function declarations. K&R style
declarations are unsupported in C++, so the include file requires
special handling when using a C++ compiler and this variable is
undefined. Consult the different d_*ndbm_h_uses_prototypes variables
to get the same information for alternative F<ndbm.h> include files.

=item C<d_nearbyint>

From F<d_nearbyint.U>:

This variable conditionally defines C<HAS_NEARBYINT> if nearbyint()
is available to return the integral value closest to (according to
the current rounding mode) to x.

=item C<d_newlocale>

From F<d_newlocale.U>:

This variable conditionally defines the C<HAS_NEWLOCALE> symbol, which
indicates to the C program that the newlocale() routine is available
to return a new locale object or modify an existing locale object.

=item C<d_nextafter>

From F<d_nextafter.U>:

This variable conditionally defines C<HAS_NEXTAFTER> if nextafter()
is available to return the next machine representable double from
x in direction y.

=item C<d_nexttoward>

From F<d_nexttoward.U>:

This variable conditionally defines C<HAS_NEXTTOWARD> if nexttoward()
is available to return the next machine representable long double from
x in direction y.

=item C<d_nice>

From F<d_nice.U>:

This variable conditionally defines the C<HAS_NICE> symbol, which
indicates to the C program that the nice() routine is available.

=item C<d_nl_langinfo>

From F<d_nl_langinfo.U>:

This variable conditionally defines the C<HAS_NL_LANGINFO> symbol, which
indicates to the C program that the nl_langinfo() routine is available.

=item C<d_nv_preserves_uv>

From F<perlxv.U>:

This variable indicates whether a variable of type nvtype
can preserve all the bits a variable of type uvtype.

=item C<d_nv_zero_is_allbits_zero>

From F<perlxv.U>:

This variable indicates whether a variable of type nvtype
stores 0.0 in memory as all bits zero.

=item C<d_off64_t>

From F<d_off64_t.U>:

This symbol will be defined if the C compiler supports off64_t.

=item C<d_old_pthread_create_joinable>

From F<d_pthrattrj.U>:

This variable conditionally defines pthread_create_joinable.
undef if F<pthread.h> defines C<PTHREAD_CREATE_JOINABLE>.

=item C<d_oldpthreads>

From F<usethreads.U>:

This variable conditionally defines the C<OLD_PTHREADS_API> symbol,
and indicates that Perl should be built to use the old
draft C<POSIX> threads C<API>. This is only potentially meaningful if
usethreads is set.

=item C<d_oldsock>

From F<d_socket.U>:

This variable conditionally defines the C<OLDSOCKET> symbol, which
indicates that the C<BSD> socket interface is based on 4.1c and not 4.2.

=item C<d_open3>

From F<d_open3.U>:

This variable conditionally defines the HAS_OPEN3 manifest constant,
which indicates to the C program that the 3 argument version of
the open(2) function is available.

=item C<d_openat>

From F<d_fsat.U>:

This variable conditionally defines the C<HAS_OPENAT> symbol, which
indicates the C<POSIX> openat() function is available.

=item C<d_pathconf>

From F<d_pathconf.U>:

This variable conditionally defines the C<HAS_PATHCONF> symbol, which
indicates to the C program that the pathconf() routine is available
to determine file-system related limits and options associated
with a given filename.

=item C<d_pause>

From F<d_pause.U>:

This variable conditionally defines the C<HAS_PAUSE> symbol, which
indicates to the C program that the pause() routine is available
to suspend a process until a signal is received.

=item C<d_perl_otherlibdirs>

From F<otherlibdirs.U>:

This variable conditionally defines C<PERL_OTHERLIBDIRS>, which
contains a colon-separated set of paths for the perl binary to
include in @C<INC>. See also otherlibdirs.

=item C<d_phostname>

From F<d_gethname.U>:

This variable conditionally defines the C<HAS_PHOSTNAME> symbol, which
contains the shell command which, when fed to popen(), may be
used to derive the host name.

=item C<d_pipe>

From F<d_pipe.U>:

This variable conditionally defines the C<HAS_PIPE> symbol, which
indicates to the C program that the pipe() routine is available
to create an inter-process channel.

=item C<d_pipe2>

From F<d_pipe2.U>:

This variable conditionally defines the HAS_PIPE2 symbol, which
indicates to the C program that the pipe2() routine is available
to create an inter-process channel.

=item C<d_poll>

From F<d_poll.U>:

This variable conditionally defines the C<HAS_POLL> symbol, which
indicates to the C program that the poll() routine is available
to poll active file descriptors.

=item C<d_portable>

From F<d_portable.U>:

This variable conditionally defines the C<PORTABLE> symbol, which
indicates to the C program that it should not assume that it is
running on the machine it was compiled on.

=item C<d_prctl>

From F<d_prctl.U>:

This variable conditionally defines the C<HAS_PRCTL> symbol, which
indicates to the C program that the prctl() routine is available.
Note that there are at least two prctl variants: Linux and Irix.
While they are somewhat similar, they are incompatible.

=item C<d_prctl_set_name>

From F<d_prctl.U>:

This variable conditionally defines the C<HAS_PRCTL_SET_NAME> symbol,
which indicates to the C program that the prctl() routine supports
the C<PR_SET_NAME> option.

=item C<d_PRId64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRId64 symbol, which
indicates that stdio has a symbol to print 64-bit decimal numbers.

=item C<d_PRIeldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.

=item C<d_PRIEUldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.
The C in the name is to separate this from d_PRIeldbl so that even
case-blind systems can see the difference.

=item C<d_PRIfldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.

=item C<d_PRIFUldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.
The C in the name is to separate this from d_PRIfldbl so that even
case-blind systems can see the difference.

=item C<d_PRIgldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.

=item C<d_PRIGUldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to print long doubles.
The C in the name is to separate this from d_PRIgldbl so that even
case-blind systems can see the difference.

=item C<d_PRIi64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRIi64 symbol, which
indicates that stdio has a symbol to print 64-bit decimal numbers.

=item C<d_printf_format_null>

From F<d_attribut.U>:

This variable conditionally defines C<PRINTF_FORMAT_NULL_OK>, which
indicates the C compiler allows printf-like formats to be null.

=item C<d_PRIo64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRIo64 symbol, which
indicates that stdio has a symbol to print 64-bit octal numbers.

=item C<d_PRIu64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRIu64 symbol, which
indicates that stdio has a symbol to print 64-bit unsigned decimal
numbers.

=item C<d_PRIx64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRIx64 symbol, which
indicates that stdio has a symbol to print 64-bit hexadecimal numbers.

=item C<d_PRIXU64>

From F<quadfio.U>:

This variable conditionally defines the PERL_PRIXU64 symbol, which
indicates that stdio has a symbol to print 64-bit hExADECimAl numbers.
The C in the name is to separate this from d_PRIx64 so that even
case-blind systems can see the difference.

=item C<d_procselfexe>

From F<d_procselfexe.U>:

Defined if $procselfexe is symlink to the absolute
pathname of the executing program.

=item C<d_pseudofork>

From F<d_vfork.U>:

This variable conditionally defines the C<HAS_PSEUDOFORK> symbol,
which indicates that an emulation of the fork routine is available.

=item C<d_pthread_atfork>

From F<d_pthread_atfork.U>:

This variable conditionally defines the C<HAS_PTHREAD_ATFORK> symbol,
which indicates to the C program that the pthread_atfork()
routine is available.

=item C<d_pthread_attr_setscope>

From F<d_pthread_attr_ss.U>:

This variable conditionally defines C<HAS_PTHREAD_ATTR_SETSCOPE> if
pthread_attr_setscope() is available to set the contention scope
attribute of a thread attribute object.

=item C<d_pthread_yield>

From F<d_pthread_y.U>:

This variable conditionally defines the C<HAS_PTHREAD_YIELD>
symbol if the pthread_yield routine is available to yield
the execution of the current thread.

=item C<d_ptrdiff_t>

From F<d_ptrdiff_t.U>:

This symbol will be defined if the C compiler supports ptrdiff_t.

=item C<d_pwage>

From F<i_pwd.U>:

This variable conditionally defines C<PWAGE>, which indicates
that struct passwd contains pw_age.

=item C<d_pwchange>

From F<i_pwd.U>:

This variable conditionally defines C<PWCHANGE>, which indicates
that struct passwd contains pw_change.

=item C<d_pwclass>

From F<i_pwd.U>:

This variable conditionally defines C<PWCLASS>, which indicates
that struct passwd contains pw_class.

=item C<d_pwcomment>

From F<i_pwd.U>:

This variable conditionally defines C<PWCOMMENT>, which indicates
that struct passwd contains pw_comment.

=item C<d_pwexpire>

From F<i_pwd.U>:

This variable conditionally defines C<PWEXPIRE>, which indicates
that struct passwd contains pw_expire.

=item C<d_pwgecos>

From F<i_pwd.U>:

This variable conditionally defines C<PWGECOS>, which indicates
that struct passwd contains pw_gecos.

=item C<d_pwpasswd>

From F<i_pwd.U>:

This variable conditionally defines C<PWPASSWD>, which indicates
that struct passwd contains pw_passwd.

=item C<d_pwquota>

From F<i_pwd.U>:

This variable conditionally defines C<PWQUOTA>, which indicates
that struct passwd contains pw_quota.

=item C<d_qgcvt>

From F<d_qgcvt.U>:

This variable conditionally defines the C<HAS_QGCVT> symbol, which
indicates to the C program that the qgcvt() routine is available.

=item C<d_quad>

From F<quadtype.U>:

This variable, if defined, tells that there's a 64-bit integer type,
quadtype.

=item C<d_querylocale>

From F<d_newlocale.U>:

This variable conditionally defines the C<HAS_QUERYLOCALE> symbol, which
indicates to the C program that the querylocale() routine is available
to return the name of the locale for a category mask.

=item C<d_random_r>

From F<d_random_r.U>:

This variable conditionally defines the C<HAS_RANDOM_R> symbol,
which indicates to the C program that the random_r()
routine is available.

=item C<d_re_comp>

From F<d_regcmp.U>:

This variable conditionally defines the C<HAS_RECOMP> symbol, which
indicates to the C program that the re_comp() routine is available
for regular pattern matching (usually on C<BSD>). If so, it is likely that
re_exec() exists.

=item C<d_readdir>

From F<d_readdir.U>:

This variable conditionally defines C<HAS_READDIR> if readdir() is
available to read directory entries.

=item C<d_readdir64_r>

From F<d_readdir64_r.U>:

This variable conditionally defines the HAS_READDIR64_R symbol,
which indicates to the C program that the readdir64_r()
routine is available.

=item C<d_readdir_r>

From F<d_readdir_r.U>:

This variable conditionally defines the C<HAS_READDIR_R> symbol,
which indicates to the C program that the readdir_r()
routine is available.

=item C<d_readlink>

From F<d_readlink.U>:

This variable conditionally defines the C<HAS_READLINK> symbol, which
indicates to the C program that the readlink() routine is available
to read the value of a symbolic link.

=item C<d_readv>

From F<d_readv.U>:

This variable conditionally defines the C<HAS_READV> symbol, which
indicates to the C program that the readv() routine is available.

=item C<d_recvmsg>

From F<d_recvmsg.U>:

This variable conditionally defines the C<HAS_RECVMSG> symbol, which
indicates to the C program that the recvmsg() routine is available.

=item C<d_regcmp>

From F<d_regcmp.U>:

This variable conditionally defines the C<HAS_REGCMP> symbol, which
indicates to the C program that the regcmp() routine is available
for regular pattern matching (usually on System V).

=item C<d_regcomp>

From F<d_regcmp.U>:

This variable conditionally defines the C<HAS_REGCOMP> symbol, which
indicates to the C program that the regcomp() routine is available
for regular pattern matching (usually on F<POSIX.2> conforming systems).

=item C<d_remainder>

From F<d_remainder.U>:

This variable conditionally defines the C<HAS_REMAINDER> symbol, which
indicates to the C program that the remainder() routine is available.

=item C<d_remquo>

From F<d_remquo.U>:

This variable conditionally defines the C<HAS_REMQUO> symbol, which
indicates to the C program that the remquo() routine is available.

=item C<d_rename>

From F<d_rename.U>:

This variable conditionally defines the C<HAS_RENAME> symbol, which
indicates to the C program that the rename() routine is available
to rename files.

=item C<d_renameat>

From F<d_fsat.U>:

This variable conditionally defines the C<HAS_RENAMEAT> symbol, which
indicates the C<POSIX> renameat() function is available.

=item C<d_rewinddir>

From F<d_readdir.U>:

This variable conditionally defines C<HAS_REWINDDIR> if rewinddir() is
available.

=item C<d_rint>

From F<d_rint.U>:

This variable conditionally defines the C<HAS_RINT> symbol, which
indicates to the C program that the rint() routine is available.

=item C<d_rmdir>

From F<d_rmdir.U>:

This variable conditionally defines C<HAS_RMDIR> if rmdir() is
available to remove directories.

=item C<d_round>

From F<d_round.U>:

This variable conditionally defines the C<HAS_ROUND> symbol, which
indicates to the C program that the round() routine is available.

=item C<d_sbrkproto>

From F<d_sbrkproto.U>:

This variable conditionally defines the C<HAS_SBRK_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the sbrk() function. Otherwise, it is
up to the program to supply one.

=item C<d_scalbn>

From F<d_scalbn.U>:

This variable conditionally defines the C<HAS_SCALBN> symbol, which
indicates to the C program that the scalbn() routine is available.

=item C<d_scalbnl>

From F<d_scalbnl.U>:

This variable conditionally defines the C<HAS_SCALBNL> symbol, which
indicates to the C program that the scalbnl() routine is available.
If ilogbl is also present we can emulate frexpl.

=item C<d_sched_yield>

From F<d_pthread_y.U>:

This variable conditionally defines the C<HAS_SCHED_YIELD>
symbol if the sched_yield routine is available to yield
the execution of the current thread.

=item C<d_scm_rights>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_SCM_RIGHTS> symbol,
which indicates that the C<SCM_RIGHTS> is available. #ifdef is
not enough because it may be an enum, glibc has been known to do this.

=item C<d_SCNfldbl>

From F<longdblfio.U>:

This variable conditionally defines the PERL_PRIfldbl symbol, which
indicates that stdio has a symbol to scan long doubles.

=item C<d_seekdir>

From F<d_readdir.U>:

This variable conditionally defines C<HAS_SEEKDIR> if seekdir() is
available.

=item C<d_select>

From F<d_select.U>:

This variable conditionally defines C<HAS_SELECT> if select() is
available to select active file descriptors. A <sys/time.h>
inclusion may be necessary for the timeout field.

=item C<d_sem>

From F<d_sem.U>:

This variable conditionally defines the C<HAS_SEM> symbol, which
indicates that the entire sem*(2) library is present.

=item C<d_semctl>

From F<d_semctl.U>:

This variable conditionally defines the C<HAS_SEMCTL> symbol, which
indicates to the C program that the semctl() routine is available.

=item C<d_semctl_semid_ds>

From F<d_union_semun.U>:

This variable conditionally defines C<USE_SEMCTL_SEMID_DS>, which
indicates that struct semid_ds * is to be used for semctl C<IPC_STAT>.

=item C<d_semctl_semun>

From F<d_union_semun.U>:

This variable conditionally defines C<USE_SEMCTL_SEMUN>, which
indicates that union semun is to be used for semctl C<IPC_STAT>.

=item C<d_semget>

From F<d_semget.U>:

This variable conditionally defines the C<HAS_SEMGET> symbol, which
indicates to the C program that the semget() routine is available.

=item C<d_semop>

From F<d_semop.U>:

This variable conditionally defines the C<HAS_SEMOP> symbol, which
indicates to the C program that the semop() routine is available.

=item C<d_sendmsg>

From F<d_sendmsg.U>:

This variable conditionally defines the C<HAS_SENDMSG> symbol, which
indicates to the C program that the sendmsg() routine is available.

=item C<d_setegid>

From F<d_setegid.U>:

This variable conditionally defines the C<HAS_SETEGID> symbol, which
indicates to the C program that the setegid() routine is available
to change the effective gid of the current program.

=item C<d_seteuid>

From F<d_seteuid.U>:

This variable conditionally defines the C<HAS_SETEUID> symbol, which
indicates to the C program that the seteuid() routine is available
to change the effective uid of the current program.

=item C<d_setgrent>

From F<d_setgrent.U>:

This variable conditionally defines the C<HAS_SETGRENT> symbol, which
indicates to the C program that the setgrent() routine is available
for initializing sequential access to the group database.

=item C<d_setgrent_r>

From F<d_setgrent_r.U>:

This variable conditionally defines the C<HAS_SETGRENT_R> symbol,
which indicates to the C program that the setgrent_r()
routine is available.

=item C<d_setgrps>

From F<d_setgrps.U>:

This variable conditionally defines the C<HAS_SETGROUPS> symbol, which
indicates to the C program that the setgroups() routine is available
to set the list of process groups.

=item C<d_sethent>

From F<d_sethent.U>:

This variable conditionally defines C<HAS_SETHOSTENT> if sethostent() is
available.

=item C<d_sethostent_r>

From F<d_sethostent_r.U>:

This variable conditionally defines the C<HAS_SETHOSTENT_R> symbol,
which indicates to the C program that the sethostent_r()
routine is available.

=item C<d_setitimer>

From F<d_setitimer.U>:

This variable conditionally defines the C<HAS_SETITIMER> symbol, which
indicates to the C program that the setitimer() routine is available.

=item C<d_setlinebuf>

From F<d_setlnbuf.U>:

This variable conditionally defines the C<HAS_SETLINEBUF> symbol, which
indicates to the C program that the setlinebuf() routine is available
to change stderr or stdout from block-buffered or unbuffered to a
line-buffered mode.

=item C<d_setlocale>

From F<d_setlocale.U>:

This variable conditionally defines C<HAS_SETLOCALE> if setlocale() is
available to handle locale-specific ctype implementations.

=item C<d_setlocale_accepts_any_locale_name>

From F<d_setlocale.U>:

This variable conditionally defines C<SETLOCALE_ACCEPTS_ANY_LOCALE_NAME>
if setlocale() accepts any locale name.

=item C<d_setlocale_r>

From F<d_setlocale_r.U>:

This variable conditionally defines the C<HAS_SETLOCALE_R> symbol,
which indicates to the C program that the setlocale_r()
routine is available.

=item C<d_setnent>

From F<d_setnent.U>:

This variable conditionally defines C<HAS_SETNETENT> if setnetent() is
available.

=item C<d_setnetent_r>

From F<d_setnetent_r.U>:

This variable conditionally defines the C<HAS_SETNETENT_R> symbol,
which indicates to the C program that the setnetent_r()
routine is available.

=item C<d_setpent>

From F<d_setpent.U>:

This variable conditionally defines C<HAS_SETPROTOENT> if setprotoent() is
available.

=item C<d_setpgid>

From F<d_setpgid.U>:

This variable conditionally defines the C<HAS_SETPGID> symbol if the
setpgid(pid, gpid) function is available to set process group C<ID>.

=item C<d_setpgrp>

From F<d_setpgrp.U>:

This variable conditionally defines C<HAS_SETPGRP> if setpgrp() is
available to set the current process group.

=item C<d_setpgrp2>

From F<d_setpgrp2.U>:

This variable conditionally defines the HAS_SETPGRP2 symbol, which
indicates to the C program that the setpgrp2() (as in F<DG/C<UX>>) routine
is available to set the current process group.

=item C<d_setprior>

From F<d_setprior.U>:

This variable conditionally defines C<HAS_SETPRIORITY> if setpriority()
is available to set a process's priority.

=item C<d_setproctitle>

From F<d_setproctitle.U>:

This variable conditionally defines the C<HAS_SETPROCTITLE> symbol,
which indicates to the C program that the setproctitle() routine
is available.

=item C<d_setprotoent_r>

From F<d_setprotoent_r.U>:

This variable conditionally defines the C<HAS_SETPROTOENT_R> symbol,
which indicates to the C program that the setprotoent_r()
routine is available.

=item C<d_setpwent>

From F<d_setpwent.U>:

This variable conditionally defines the C<HAS_SETPWENT> symbol, which
indicates to the C program that the setpwent() routine is available
for initializing sequential access to the passwd database.

=item C<d_setpwent_r>

From F<d_setpwent_r.U>:

This variable conditionally defines the C<HAS_SETPWENT_R> symbol,
which indicates to the C program that the setpwent_r()
routine is available.

=item C<d_setregid>

From F<d_setregid.U>:

This variable conditionally defines C<HAS_SETREGID> if setregid() is
available to change the real and effective gid of the current
process.

=item C<d_setresgid>

From F<d_setregid.U>:

This variable conditionally defines C<HAS_SETRESGID> if setresgid() is
available to change the real, effective and saved gid of the current
process.

=item C<d_setresuid>

From F<d_setreuid.U>:

This variable conditionally defines C<HAS_SETREUID> if setresuid() is
available to change the real, effective and saved uid of the current
process.

=item C<d_setreuid>

From F<d_setreuid.U>:

This variable conditionally defines C<HAS_SETREUID> if setreuid() is
available to change the real and effective uid of the current
process.

=item C<d_setrgid>

From F<d_setrgid.U>:

This variable conditionally defines the C<HAS_SETRGID> symbol, which
indicates to the C program that the setrgid() routine is available
to change the real gid of the current program.

=item C<d_setruid>

From F<d_setruid.U>:

This variable conditionally defines the C<HAS_SETRUID> symbol, which
indicates to the C program that the setruid() routine is available
to change the real uid of the current program.

=item C<d_setsent>

From F<d_setsent.U>:

This variable conditionally defines C<HAS_SETSERVENT> if setservent() is
available.

=item C<d_setservent_r>

From F<d_setservent_r.U>:

This variable conditionally defines the C<HAS_SETSERVENT_R> symbol,
which indicates to the C program that the setservent_r()
routine is available.

=item C<d_setsid>

From F<d_setsid.U>:

This variable conditionally defines C<HAS_SETSID> if setsid() is
available to set the process group C<ID>.

=item C<d_setvbuf>

From F<d_setvbuf.U>:

This variable conditionally defines the C<HAS_SETVBUF> symbol, which
indicates to the C program that the setvbuf() routine is available
to change buffering on an open stdio stream.

=item C<d_shm>

From F<d_shm.U>:

This variable conditionally defines the C<HAS_SHM> symbol, which
indicates that the entire shm*(2) library is present.

=item C<d_shmat>

From F<d_shmat.U>:

This variable conditionally defines the C<HAS_SHMAT> symbol, which
indicates to the C program that the shmat() routine is available.

=item C<d_shmatprototype>

From F<d_shmat.U>:

This variable conditionally defines the C<HAS_SHMAT_PROTOTYPE>
symbol, which indicates that F<sys/shm.h> has a prototype for
shmat.

=item C<d_shmctl>

From F<d_shmctl.U>:

This variable conditionally defines the C<HAS_SHMCTL> symbol, which
indicates to the C program that the shmctl() routine is available.

=item C<d_shmdt>

From F<d_shmdt.U>:

This variable conditionally defines the C<HAS_SHMDT> symbol, which
indicates to the C program that the shmdt() routine is available.

=item C<d_shmget>

From F<d_shmget.U>:

This variable conditionally defines the C<HAS_SHMGET> symbol, which
indicates to the C program that the shmget() routine is available.

=item C<d_sigaction>

From F<d_sigaction.U>:

This variable conditionally defines the C<HAS_SIGACTION> symbol, which
indicates that the Vr4 sigaction() routine is available.

=item C<d_siginfo_si_addr>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_ADDR> symbol,
which indicates that the siginfo_t struct has the si_addr member.

=item C<d_siginfo_si_band>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_BAND> symbol,
which indicates that the siginfo_t struct has the si_band member.

=item C<d_siginfo_si_errno>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_ERRNO> symbol,
which indicates that the siginfo_t struct has the si_errno member.

=item C<d_siginfo_si_fd>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_FD> symbol,
which indicates that the siginfo_t struct has the si_fd member.

=item C<d_siginfo_si_pid>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_PID> symbol,
which indicates that the siginfo_t struct has the si_pid member.

=item C<d_siginfo_si_status>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_STATUS> symbol,
which indicates that the siginfo_t struct has the si_status member.

=item C<d_siginfo_si_uid>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_UID> symbol,
which indicates that the siginfo_t struct has the si_uid member.

=item C<d_siginfo_si_value>

From F<d_siginfo_si.U>:

This variable conditionally defines the C<HAS_SIGINFO_SI_VALUE> symbol,
which indicates that the siginfo_t struct has the si_value member.

=item C<d_signbit>

From F<d_signbit.U>:

This variable conditionally defines the C<HAS_SIGNBIT> symbol, which
indicates to the C program that the signbit() routine is available
and safe to use with perl's intern C<NV> type.

=item C<d_sigprocmask>

From F<d_sigprocmask.U>:

This variable conditionally defines C<HAS_SIGPROCMASK>
if sigprocmask() is available to examine or change the signal mask
of the calling process.

=item C<d_sigsetjmp>

From F<d_sigsetjmp.U>:

This variable conditionally defines the C<HAS_SIGSETJMP> symbol,
which indicates that the sigsetjmp() routine is available to
call setjmp() and optionally save the process's signal mask.

=item C<d_sin6_scope_id>

From F<d_socket.U>:

This variable conditionally defines the HAS_SIN6_SCOPE_ID symbol, which
indicates that a struct sockaddr_in6 structure has the sin6_scope_id
member.

=item C<d_sitearch>

From F<sitearch.U>:

This variable conditionally defines C<SITEARCH> to hold the pathname
of architecture-dependent library files for $package. If
$sitearch is the same as $archlib, then this is set to undef.

=item C<d_snprintf>

From F<d_snprintf.U>:

This variable conditionally defines the C<HAS_SNPRINTF> symbol, which
indicates to the C program that the snprintf () library function
is available.

=item C<d_sockaddr_in6>

From F<d_socket.U>:

This variable conditionally defines the HAS_SOCKADDR_IN6 symbol, which
indicates the availability of a struct sockaddr_in6.

=item C<d_sockaddr_sa_len>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_SOCKADDR_SA_LEN> symbol,
which indicates that a struct sockaddr structure has the sa_len
member.

=item C<d_sockatmark>

From F<d_sockatmark.U>:

This variable conditionally defines the C<HAS_SOCKATMARK> symbol, which
indicates to the C program that the sockatmark() routine is available.

=item C<d_sockatmarkproto>

From F<d_sockatmarkproto.U>:

This variable conditionally defines the C<HAS_SOCKATMARK_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the sockatmark() function. Otherwise, it is
up to the program to supply one.

=item C<d_socket>

From F<d_socket.U>:

This variable conditionally defines C<HAS_SOCKET>, which indicates
that the C<BSD> socket interface is supported.

=item C<d_socklen_t>

From F<d_socklen_t.U>:

This symbol will be defined if the C compiler supports socklen_t.

=item C<d_sockpair>

From F<d_socket.U>:

This variable conditionally defines the C<HAS_SOCKETPAIR> symbol, which
indicates that the C<BSD> socketpair() is supported.

=item C<d_socks5_init>

From F<d_socks5_init.U>:

This variable conditionally defines the HAS_SOCKS5_INIT symbol, which
indicates to the C program that the socks5_init() routine is available.

=item C<d_sqrtl>

From F<d_sqrtl.U>:

This variable conditionally defines the C<HAS_SQRTL> symbol, which
indicates to the C program that the sqrtl() routine is available.

=item C<d_srand48_r>

From F<d_srand48_r.U>:

This variable conditionally defines the HAS_SRAND48_R symbol,
which indicates to the C program that the srand48_r()
routine is available.

=item C<d_srandom_r>

From F<d_srandom_r.U>:

This variable conditionally defines the C<HAS_SRANDOM_R> symbol,
which indicates to the C program that the srandom_r()
routine is available.

=item C<d_sresgproto>

From F<d_sresgproto.U>:

This variable conditionally defines the C<HAS_SETRESGID_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the setresgid() function. Otherwise, it is
up to the program to supply one.

=item C<d_sresuproto>

From F<d_sresuproto.U>:

This variable conditionally defines the C<HAS_SETRESUID_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the setresuid() function. Otherwise, it is
up to the program to supply one.

=item C<d_stat>

From F<d_stat.U>:

This variable conditionally defines C<HAS_STAT> if stat() is
available to get file status.

=item C<d_statblks>

From F<d_statblks.U>:

This variable conditionally defines C<USE_STAT_BLOCKS>
if this system has a stat structure declaring
st_blksize and st_blocks.

=item C<d_statfs_f_flags>

From F<d_statfs_f_flags.U>:

This variable conditionally defines the C<HAS_STRUCT_STATFS_F_FLAGS>
symbol, which indicates to struct statfs from has f_flags member.
This kind of struct statfs is coming from F<sys/mount.h> (C<BSD>),
not from F<sys/statfs.h> (C<SYSV>).

=item C<d_statfs_s>

From F<d_statfs_s.U>:

This variable conditionally defines the C<HAS_STRUCT_STATFS> symbol,
which indicates that the struct statfs is supported.

=item C<d_static_inline>

From F<d_static_inline.U>:

This variable conditionally defines the C<HAS_STATIC_INLINE> symbol,
which indicates that the C compiler supports C99-style static
inline. That is, the function can't be called from another
translation unit.

=item C<d_statvfs>

From F<d_statvfs.U>:

This variable conditionally defines the C<HAS_STATVFS> symbol, which
indicates to the C program that the statvfs() routine is available.

=item C<d_stdio_cnt_lval>

From F<d_stdstdio.U>:

This variable conditionally defines C<STDIO_CNT_LVALUE> if the
C<FILE_cnt> macro can be used as an lvalue.

=item C<d_stdio_ptr_lval>

From F<d_stdstdio.U>:

This variable conditionally defines C<STDIO_PTR_LVALUE> if the
C<FILE_ptr> macro can be used as an lvalue.

=item C<d_stdio_ptr_lval_nochange_cnt>

From F<d_stdstdio.U>:

This symbol is defined if using the C<FILE_ptr> macro as an lvalue
to increase the pointer by n leaves File_cnt(fp) unchanged.

=item C<d_stdio_ptr_lval_sets_cnt>

From F<d_stdstdio.U>:

This symbol is defined if using the C<FILE_ptr> macro as an lvalue
to increase the pointer by n has the side effect of decreasing the
value of File_cnt(fp) by n.

=item C<d_stdio_stream_array>

From F<stdio_streams.U>:

This variable tells whether there is an array holding
the stdio streams.

=item C<d_stdiobase>

From F<d_stdstdio.U>:

This variable conditionally defines C<USE_STDIO_BASE> if this system
has a C<FILE> structure declaring a usable _base field (or equivalent)
in F<stdio.h>.

=item C<d_stdstdio>

From F<d_stdstdio.U>:

This variable conditionally defines C<USE_STDIO_PTR> if this system
has a C<FILE> structure declaring usable _ptr and _cnt fields (or
equivalent) in F<stdio.h>.

=item C<d_strcoll>

From F<d_strcoll.U>:

This variable conditionally defines C<HAS_STRCOLL> if strcoll() is
available to compare strings using collating information.

=item C<d_strerror_l>

From F<d_strerror_l.U>:

This variable conditionally defines the C<HAS_STRERROR_L> symbol, which
indicates to the C program that the strerror_l() routine is available
to return the error message for a given errno value in a particular
locale (identified by a locale_t object).

=item C<d_strerror_r>

From F<d_strerror_r.U>:

This variable conditionally defines the C<HAS_STRERROR_R> symbol,
which indicates to the C program that the strerror_r()
routine is available.

=item C<d_strftime>

From F<d_strftime.U>:

This variable conditionally defines the C<HAS_STRFTIME> symbol, which
indicates to the C program that the strftime() routine is available.

=item C<d_strlcat>

From F<d_strlcat.U>:

This variable conditionally defines the C<HAS_STRLCAT> symbol, which
indicates to the C program that the strlcat () routine is available.

=item C<d_strlcpy>

From F<d_strlcpy.U>:

This variable conditionally defines the C<HAS_STRLCPY> symbol, which
indicates to the C program that the strlcpy () routine is available.

=item C<d_strnlen>

From F<d_strnlen.U>:

This variable conditionally defines the C<HAS_STRNLEN> symbol, which
indicates to the C program that the strnlen () routine is available.

=item C<d_strtod>

From F<d_strtod.U>:

This variable conditionally defines the C<HAS_STRTOD> symbol, which
indicates to the C program that the strtod() routine is available
to provide better numeric string conversion than atof().

=item C<d_strtod_l>

From F<d_strtod_l.U>:

This variable conditionally defines the C<HAS_STRTOD_L> symbol, which
indicates to the C program that the strtod_l() routine is available.

=item C<d_strtol>

From F<d_strtol.U>:

This variable conditionally defines the C<HAS_STRTOL> symbol, which
indicates to the C program that the strtol() routine is available
to provide better numeric string conversion than atoi() and friends.

=item C<d_strtold>

From F<d_strtold.U>:

This variable conditionally defines the C<HAS_STRTOLD> symbol, which
indicates to the C program that the strtold() routine is available.

=item C<d_strtold_l>

From F<d_strtold_l.U>:

This variable conditionally defines the C<HAS_STRTOLD_L> symbol, which
indicates to the C program that the strtold_l() routine is available.

=item C<d_strtoll>

From F<d_strtoll.U>:

This variable conditionally defines the C<HAS_STRTOLL> symbol, which
indicates to the C program that the strtoll() routine is available.

=item C<d_strtoq>

From F<d_strtoq.U>:

This variable conditionally defines the C<HAS_STRTOQ> symbol, which
indicates to the C program that the strtoq() routine is available.

=item C<d_strtoul>

From F<d_strtoul.U>:

This variable conditionally defines the C<HAS_STRTOUL> symbol, which
indicates to the C program that the strtoul() routine is available
to provide conversion of strings to unsigned long.

=item C<d_strtoull>

From F<d_strtoull.U>:

This variable conditionally defines the C<HAS_STRTOULL> symbol, which
indicates to the C program that the strtoull() routine is available.

=item C<d_strtouq>

From F<d_strtouq.U>:

This variable conditionally defines the C<HAS_STRTOUQ> symbol, which
indicates to the C program that the strtouq() routine is available.

=item C<d_strxfrm>

From F<d_strxfrm.U>:

This variable conditionally defines C<HAS_STRXFRM> if strxfrm() is
available to transform strings.

=item C<d_suidsafe>

From F<d_dosuid.U>:

This variable conditionally defines C<SETUID_SCRIPTS_ARE_SECURE_NOW>
if setuid scripts can be secure. This test looks in F</dev/fd/>.

=item C<d_symlink>

From F<d_symlink.U>:

This variable conditionally defines the C<HAS_SYMLINK> symbol, which
indicates to the C program that the symlink() routine is available
to create symbolic links.

=item C<d_syscall>

From F<d_syscall.U>:

This variable conditionally defines C<HAS_SYSCALL> if syscall() is
available call arbitrary system calls.

=item C<d_syscallproto>

From F<d_syscallproto.U>:

This variable conditionally defines the C<HAS_SYSCALL_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the syscall() function. Otherwise, it is
up to the program to supply one.

=item C<d_sysconf>

From F<d_sysconf.U>:

This variable conditionally defines the C<HAS_SYSCONF> symbol, which
indicates to the C program that the sysconf() routine is available
to determine system related limits and options.

=item C<d_sysernlst>

From F<d_strerror.U>:

This variable conditionally defines C<HAS_SYS_ERRNOLIST> if sys_errnolist[]
is available to translate error numbers to the symbolic name.

=item C<d_syserrlst>

From F<d_strerror.U>:

This variable conditionally defines C<HAS_SYS_ERRLIST> if sys_errlist[] is
available to translate error numbers to strings.

=item C<d_system>

From F<d_system.U>:

This variable conditionally defines C<HAS_SYSTEM> if system() is
available to issue a shell command.

=item C<d_tcgetpgrp>

From F<d_tcgtpgrp.U>:

This variable conditionally defines the C<HAS_TCGETPGRP> symbol, which
indicates to the C program that the tcgetpgrp() routine is available.
to get foreground process group C<ID>.

=item C<d_tcsetpgrp>

From F<d_tcstpgrp.U>:

This variable conditionally defines the C<HAS_TCSETPGRP> symbol, which
indicates to the C program that the tcsetpgrp() routine is available
to set foreground process group C<ID>.

=item C<d_telldir>

From F<d_readdir.U>:

This variable conditionally defines C<HAS_TELLDIR> if telldir() is
available.

=item C<d_telldirproto>

From F<d_telldirproto.U>:

This variable conditionally defines the C<HAS_TELLDIR_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the telldir() function. Otherwise, it is
up to the program to supply one.

=item C<d_tgamma>

From F<d_tgamma.U>:

This variable conditionally defines the C<HAS_TGAMMA> symbol, which
indicates to the C program that the tgamma() routine is available
for the gamma function. See also d_lgamma.

=item C<d_thread_safe_nl_langinfo_l>

From F<d_nl_langinfo_l.U>:

This variable contains the eventual value of the
C<HAS_THREAD_SAFE_NL_LANGINFO_L> symbol, which indicates if the
nl_langinfo_l() function exists and is thread-safe.

=item C<d_time>

From F<d_time.U>:

This variable conditionally defines the C<HAS_TIME> symbol, which indicates
that the time() routine exists. The time() routine is normally
provided on C<UNIX> systems.

=item C<d_timegm>

From F<d_timegm.U>:

This variable conditionally defines the C<HAS_TIMEGM> symbol, which
indicates to the C program that the timegm () routine is available.

=item C<d_times>

From F<d_times.U>:

This variable conditionally defines the C<HAS_TIMES> symbol, which indicates
that the times() routine exists. The times() routine is normally
provided on C<UNIX> systems. You may have to include <sys/times.h>.

=item C<d_tm_tm_gmtoff>

From F<i_time.U>:

This variable conditionally defines C<HAS_TM_TM_GMTOFF>, which indicates
to the C program that the struct tm has the tm_gmtoff field.

=item C<d_tm_tm_zone>

From F<i_time.U>:

This variable conditionally defines C<HAS_TM_TM_ZONE>, which indicates
to the C program that the struct tm has the tm_zone field.

=item C<d_tmpnam_r>

From F<d_tmpnam_r.U>:

This variable conditionally defines the C<HAS_TMPNAM_R> symbol,
which indicates to the C program that the tmpnam_r()
routine is available.

=item C<d_towlower>

From F<d_towlower.U>:

This variable conditionally defines the C<HAS_TOWLOWER> symbol, which
indicates to the C program that the towlower() routine is available.

=item C<d_towupper>

From F<d_towupper.U>:

This variable conditionally defines the C<HAS_TOWUPPER> symbol, which
indicates to the C program that the towupper() routine is available.

=item C<d_trunc>

From F<d_trunc.U>:

This variable conditionally defines the C<HAS_TRUNC> symbol, which
indicates to the C program that the trunc() routine is available
to round doubles towards zero.

=item C<d_truncate>

From F<d_truncate.U>:

This variable conditionally defines C<HAS_TRUNCATE> if truncate() is
available to truncate files.

=item C<d_truncl>

From F<d_truncl.U>:

This variable conditionally defines the C<HAS_TRUNCL> symbol, which
indicates to the C program that the truncl() routine is available
to round long doubles towards zero. If copysignl is also present,
we can emulate modfl.

=item C<d_ttyname_r>

From F<d_ttyname_r.U>:

This variable conditionally defines the C<HAS_TTYNAME_R> symbol,
which indicates to the C program that the ttyname_r()
routine is available.

=item C<d_tzname>

From F<d_tzname.U>:

This variable conditionally defines C<HAS_TZNAME> if tzname[] is
available to access timezone names.

=item C<d_u32align>

From F<d_u32align.U>:

This variable tells whether you must access character data
through U32-aligned pointers.

=item C<d_ualarm>

From F<d_ualarm.U>:

This variable conditionally defines the C<HAS_UALARM> symbol, which
indicates to the C program that the ualarm() routine is available.

=item C<d_umask>

From F<d_umask.U>:

This variable conditionally defines the C<HAS_UMASK> symbol, which
indicates to the C program that the umask() routine is available.
to set and get the value of the file creation mask.

=item C<d_uname>

From F<d_gethname.U>:

This variable conditionally defines the C<HAS_UNAME> symbol, which
indicates to the C program that the uname() routine may be
used to derive the host name.

=item C<d_union_semun>

From F<d_union_semun.U>:

This variable conditionally defines C<HAS_UNION_SEMUN> if the
union semun is defined by including <sys/sem.h>.

=item C<d_unlinkat>

From F<d_fsat.U>:

This variable conditionally defines the C<HAS_UNLINKAT> symbol, which
indicates the C<POSIX> unlinkat() function isavailable.

=item C<d_unordered>

From F<d_unordered.U>:

This variable conditionally defines the C<HAS_UNORDERED> symbol, which
indicates to the C program that the unordered() routine is available.

=item C<d_unsetenv>

From F<d_unsetenv.U>:

This variable conditionally defines the C<HAS_UNSETENV> symbol, which
indicates to the C program that the unsetenv () routine is available.

=item C<d_uselocale>

From F<d_newlocale.U>:

This variable conditionally defines the C<HAS_USELOCALE> symbol, which
indicates to the C program that the uselocale() routine is available
to set the current locale for the calling thread.

=item C<d_usleep>

From F<d_usleep.U>:

This variable conditionally defines C<HAS_USLEEP> if usleep() is
available to do high granularity sleeps.

=item C<d_usleepproto>

From F<d_usleepproto.U>:

This variable conditionally defines the C<HAS_USLEEP_PROTO> symbol,
which indicates to the C program that the system provides
a prototype for the usleep() function. Otherwise, it is
up to the program to supply one.

=item C<d_ustat>

From F<d_ustat.U>:

This variable conditionally defines C<HAS_USTAT> if ustat() is
available to query file system statistics by dev_t.

=item C<d_vendorarch>

From F<vendorarch.U>:

This variable conditionally defined C<PERL_VENDORARCH>.

=item C<d_vendorbin>

From F<vendorbin.U>:

This variable conditionally defines C<PERL_VENDORBIN>.

=item C<d_vendorlib>

From F<vendorlib.U>:

This variable conditionally defines C<PERL_VENDORLIB>.

=item C<d_vendorscript>

From F<vendorscript.U>:

This variable conditionally defines C<PERL_VENDORSCRIPT>.

=item C<d_vfork>

From F<d_vfork.U>:

This variable conditionally defines the C<HAS_VFORK> symbol, which
indicates the vfork() routine is available.

=item C<d_void_closedir>

From F<d_closedir.U>:

This variable conditionally defines C<VOID_CLOSEDIR> if closedir()
does not return a value.

=item C<d_voidsig>

From F<d_voidsig.U>:

This variable conditionally defines C<VOIDSIG> if this system
declares "void (*signal(...))()" in F<signal.h>. The old way was to
declare it as "int (*signal(...))()".

=item C<d_voidtty>

From F<i_sysioctl.U>:

This variable conditionally defines C<USE_IOCNOTTY> to indicate that the
ioctl() call with C<TIOCNOTTY> should be used to void tty association.
Otherwise (on C<USG> probably), it is enough to close the standard file
descriptors and do a setpgrp().

=item C<d_vsnprintf>

From F<d_snprintf.U>:

This variable conditionally defines the C<HAS_VSNPRINTF> symbol, which
indicates to the C program that the vsnprintf () library function
is available.

=item C<d_wait4>

From F<d_wait4.U>:

This variable conditionally defines the HAS_WAIT4 symbol, which
indicates the wait4() routine is available.

=item C<d_waitpid>

From F<d_waitpid.U>:

This variable conditionally defines C<HAS_WAITPID> if waitpid() is
available to wait for child process.

=item C<d_wcscmp>

From F<d_wcscmp.U>:

This variable conditionally defines the C<HAS_WCSCMP> symbol if the
wcscmp() routine is available and can be used to compare wide
character strings.

=item C<d_wcstombs>

From F<d_wcstombs.U>:

This variable conditionally defines the C<HAS_WCSTOMBS> symbol, which
indicates to the C program that the wcstombs() routine is available
to convert wide character strings to multibyte strings.

=item C<d_wcsxfrm>

From F<d_wcsxfrm.U>:

This variable conditionally defines the C<HAS_WCSXFRM> symbol if the
wcsxfrm() routine is available and can be used to compare wide
character strings.

=item C<d_wctomb>

From F<d_wctomb.U>:

This variable conditionally defines the C<HAS_WCTOMB> symbol, which
indicates to the C program that the wctomb() routine is available
to convert a wide character to a multibyte.

=item C<d_writev>

From F<d_writev.U>:

This variable conditionally defines the C<HAS_WRITEV> symbol, which
indicates to the C program that the writev() routine is available.

=item C<d_xenix>

From F<Guess.U>:

This variable conditionally defines the symbol C<XENIX>, which alerts
the C program that it runs under Xenix.

=item C<date>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the date program. After Configure runs,
the value is reset to a plain C<date> and is not useful.

=item C<db_hashtype>

From F<i_db.U>:

This variable contains the type of the hash structure element
in the <db.h> header file. In older versions of C<DB>, it was
int, while in newer ones it is u_int32_t.

=item C<db_prefixtype>

From F<i_db.U>:

This variable contains the type of the prefix structure element
in the <db.h> header file. In older versions of C<DB>, it was
int, while in newer ones it is size_t.

=item C<db_version_major>

From F<i_db.U>:

This variable contains the major version number of
Berkeley C<DB> found in the <db.h> header file.

=item C<db_version_minor>

From F<i_db.U>:

This variable contains the minor version number of
Berkeley C<DB> found in the <db.h> header file.
For C<DB> version 1 this is always 0.

=item C<db_version_patch>

From F<i_db.U>:

This variable contains the patch version number of
Berkeley C<DB> found in the <db.h> header file.
For C<DB> version 1 this is always 0.

=item C<default_inc_excludes_dot>

From F<defaultincdot.U>:

When defined, remove the legacy F<.> from @C<INC>

=item C<direntrytype>

From F<i_dirent.U>:

This symbol is set to C<struct direct> or C<struct dirent> depending on
whether dirent is available or not. You should use this pseudo type to
portably declare your directory entries.

=item C<dlext>

From F<dlext.U>:

This variable contains the extension that is to be used for the
dynamically loaded modules that perl generates.

=item C<dlsrc>

From F<dlsrc.U>:

This variable contains the name of the dynamic loading file that
will be used with the package.

=item C<doubleinfbytes>

From F<infnan.U>:

This variable contains comma-separated list of hexadecimal bytes
for the double precision infinity.

=item C<doublekind>

From F<longdblfio.U>:

This variable, if defined, encodes the type of a double:
1 = C<IEEE> 754 32-bit little endian,
2 = C<IEEE> 754 32-bit big endian,
3 = C<IEEE> 754 64-bit little endian,
4 = C<IEEE> 754 64-bit big endian,
5 = C<IEEE> 754 128-bit little endian,
6 = C<IEEE> 754 128-bit big endian,
7 = C<IEEE> 754 64-bit mixed endian le-be,
8 = C<IEEE> 754 64-bit mixed endian be-le,
9 = C<VAX> 32bit little endian F float format
10 = C<VAX> 64bit little endian D float format
11 = C<VAX> 64bit little endian G float format
12 = C<IBM> 32bit format
13 = C<IBM> 64bit format
14 = Cray 64bit format
-1 = unknown format.

=item C<doublemantbits>

From F<mantbits.U>:

This symbol, if defined, tells how many mantissa bits
there are in double precision floating point format.
Note that this is usually C<DBL_MANT_DIG> minus one, since
with the standard C<IEEE> 754 formats C<DBL_MANT_DIG> includes
the implicit bit which doesn't really exist.

=item C<doublenanbytes>

From F<infnan.U>:

This variable contains comma-separated list of hexadecimal bytes
for the double precision not-a-number.

=item C<doublesize>

From F<doublesize.U>:

This variable contains the value of the C<DOUBLESIZE> symbol, which
indicates to the C program how many bytes there are in a double.

=item C<drand01>

From F<randfunc.U>:

Indicates the macro to be used to generate normalized
random numbers. Uses randfunc, often divided by
(double) (((unsigned long) 1 << randbits)) in order to
normalize the result.
In C programs, the macro C<Drand01> is mapped to drand01.

=item C<drand48_r_proto>

From F<d_drand48_r.U>:

This variable encodes the prototype of drand48_r.
It is zero if d_drand48_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_drand48_r
is defined.

=item C<dtrace>

From F<usedtrace.U>:

This variable holds the location of the dtrace executable.

=item C<dtraceobject>

From F<dtraceobject.U>:

Whether we need to build an object file with the dtrace tool.

=item C<dtracexnolibs>

From F<dtraceobject.U>:

Whether dtrace accepts -xnolibs.  If available we call dtrace -h
and dtrace -G with -xnolibs to allow dtrace to run in a jail on
FreeBSD.

=item C<dynamic_ext>

From F<Extensions.U>:

This variable holds a list of C<XS> extension files we want to
link dynamically into the package. It is used by Makefile.

=back

=head2 e

=over 4

=item C<eagain>

From F<nblock_io.U>:

This variable bears the symbolic errno code set by read() when no
data is present on the file and non-blocking I/O was enabled (otherwise,
read() blocks naturally).

=item C<ebcdic>

From F<ebcdic.U>:

This variable conditionally defines C<EBCDIC> if this
system uses C<EBCDIC> encoding.

=item C<echo>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the echo program. After Configure runs,
the value is reset to a plain C<echo> and is not useful.

=item C<egrep>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the egrep program. After Configure runs,
the value is reset to a plain C<egrep> and is not useful.

=item C<emacs>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<endgrent_r_proto>

From F<d_endgrent_r.U>:

This variable encodes the prototype of endgrent_r.
It is zero if d_endgrent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endgrent_r
is defined.

=item C<endhostent_r_proto>

From F<d_endhostent_r.U>:

This variable encodes the prototype of endhostent_r.
It is zero if d_endhostent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endhostent_r
is defined.

=item C<endnetent_r_proto>

From F<d_endnetent_r.U>:

This variable encodes the prototype of endnetent_r.
It is zero if d_endnetent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endnetent_r
is defined.

=item C<endprotoent_r_proto>

From F<d_endprotoent_r.U>:

This variable encodes the prototype of endprotoent_r.
It is zero if d_endprotoent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endprotoent_r
is defined.

=item C<endpwent_r_proto>

From F<d_endpwent_r.U>:

This variable encodes the prototype of endpwent_r.
It is zero if d_endpwent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endpwent_r
is defined.

=item C<endservent_r_proto>

From F<d_endservent_r.U>:

This variable encodes the prototype of endservent_r.
It is zero if d_endservent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_endservent_r
is defined.

=item C<eunicefix>

From F<Init.U>:

When running under Eunice this variable contains a command which will
convert a shell script to the proper form of text file for it to be
executable by the shell.  On other systems it is a no-op.

=item C<exe_ext>

From F<Unix.U>:

This is an old synonym for _exe.

=item C<expr>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the expr program. After Configure runs,
the value is reset to a plain C<expr> and is not useful.

=item C<extensions>

From F<Extensions.U>:

This variable holds a list of all extension files (both C<XS> and
non-xs) installed with the package. It is propagated to F<Config.pm>
and is typically used to test whether a particular extension
is available.

=item C<extern_C>

From F<Csym.U>:

C<ANSI> C requires C<extern> where C++ requires 'extern C<C>'. This
variable can be used in Configure to do the right thing.

=item C<extras>

From F<Extras.U>:

This variable holds a list of extra modules to install.

=back

=head2 f

=over 4

=item C<fflushall>

From F<fflushall.U>:

This symbol, if defined, tells that to flush
all pending stdio output one must loop through all
the stdio file handles stored in an array and fflush them.
Note that if fflushNULL is defined, fflushall will not
even be probed for and will be left undefined.

=item C<fflushNULL>

From F<fflushall.U>:

This symbol, if defined, tells that fflush(C<NULL>) correctly
flushes all pending stdio output without side effects. In
particular, on some platforms calling fflush(C<NULL>) *still*
corrupts C<STDIN> if it is a pipe.

=item C<find>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<firstmakefile>

From F<Unix.U>:

This variable defines the first file searched by make.  On unix,
it is makefile (then Makefile).  On case-insensitive systems,
it might be something else.  This is only used to deal with
convoluted make depend tricks.

=item C<flex>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<fpossize>

From F<fpossize.U>:

This variable contains the size of a fpostype in bytes.

=item C<fpostype>

From F<fpostype.U>:

This variable defines Fpos_t to be something like fpos_t, long,
uint, or whatever type is used to declare file positions in libc.

=item C<freetype>

From F<mallocsrc.U>:

This variable contains the return type of free().  It is usually
void, but occasionally int.

=item C<from>

From F<Cross.U>:

This variable contains the command used by Configure
to copy files from the target host. Useful and available
only during Perl build.
The string C<:> if not cross-compiling.

=item C<full_ar>

From F<Loc_ar.U>:

This variable contains the full pathname to C<ar>, whether or
not the user has specified C<portability>. This is only used
in the F<Makefile.SH>.

=item C<full_csh>

From F<d_csh.U>:

This variable contains the full pathname to C<csh>, whether or
not the user has specified C<portability>. This is only used
in the compiled C program, and we assume that all systems which
can share this executable will have the same full pathname to
F<csh.>

=item C<full_sed>

From F<Loc_sed.U>:

This variable contains the full pathname to C<sed>, whether or
not the user has specified C<portability>. This is only used
in the compiled C program, and we assume that all systems which
can share this executable will have the same full pathname to
F<sed.>

=back

=head2 g

=over 4

=item C<gccansipedantic>

From F<gccvers.U>:

If C<GNU> cc (gcc) is used, this variable will enable (if set) the
-ansi and -pedantic ccflags for building core files (through
cflags script). (See F<Porting/pumpkin.pod> for full description).

=item C<gccosandvers>

From F<gccvers.U>:

If C<GNU> cc (gcc) is used, this variable holds the operating system
and version used to compile gcc. It is set to '' if not gcc,
or if nothing useful can be parsed as the os version.

=item C<gccversion>

From F<gccvers.U>:

If C<GNU> cc (gcc) is used, this variable holds C<1> or C<2> to
indicate whether the compiler is version 1 or 2. This is used in
setting some of the default cflags. It is set to '' if not gcc.

=item C<getgrent_r_proto>

From F<d_getgrent_r.U>:

This variable encodes the prototype of getgrent_r.
It is zero if d_getgrent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getgrent_r
is defined.

=item C<getgrgid_r_proto>

From F<d_getgrgid_r.U>:

This variable encodes the prototype of getgrgid_r.
It is zero if d_getgrgid_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getgrgid_r
is defined.

=item C<getgrnam_r_proto>

From F<d_getgrnam_r.U>:

This variable encodes the prototype of getgrnam_r.
It is zero if d_getgrnam_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getgrnam_r
is defined.

=item C<gethostbyaddr_r_proto>

From F<d_gethostbyaddr_r.U>:

This variable encodes the prototype of gethostbyaddr_r.
It is zero if d_gethostbyaddr_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_gethostbyaddr_r
is defined.

=item C<gethostbyname_r_proto>

From F<d_gethostbyname_r.U>:

This variable encodes the prototype of gethostbyname_r.
It is zero if d_gethostbyname_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_gethostbyname_r
is defined.

=item C<gethostent_r_proto>

From F<d_gethostent_r.U>:

This variable encodes the prototype of gethostent_r.
It is zero if d_gethostent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_gethostent_r
is defined.

=item C<getlogin_r_proto>

From F<d_getlogin_r.U>:

This variable encodes the prototype of getlogin_r.
It is zero if d_getlogin_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getlogin_r
is defined.

=item C<getnetbyaddr_r_proto>

From F<d_getnetbyaddr_r.U>:

This variable encodes the prototype of getnetbyaddr_r.
It is zero if d_getnetbyaddr_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getnetbyaddr_r
is defined.

=item C<getnetbyname_r_proto>

From F<d_getnetbyname_r.U>:

This variable encodes the prototype of getnetbyname_r.
It is zero if d_getnetbyname_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getnetbyname_r
is defined.

=item C<getnetent_r_proto>

From F<d_getnetent_r.U>:

This variable encodes the prototype of getnetent_r.
It is zero if d_getnetent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getnetent_r
is defined.

=item C<getprotobyname_r_proto>

From F<d_getprotobyname_r.U>:

This variable encodes the prototype of getprotobyname_r.
It is zero if d_getprotobyname_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getprotobyname_r
is defined.

=item C<getprotobynumber_r_proto>

From F<d_getprotobynumber_r.U>:

This variable encodes the prototype of getprotobynumber_r.
It is zero if d_getprotobynumber_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getprotobynumber_r
is defined.

=item C<getprotoent_r_proto>

From F<d_getprotoent_r.U>:

This variable encodes the prototype of getprotoent_r.
It is zero if d_getprotoent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getprotoent_r
is defined.

=item C<getpwent_r_proto>

From F<d_getpwent_r.U>:

This variable encodes the prototype of getpwent_r.
It is zero if d_getpwent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getpwent_r
is defined.

=item C<getpwnam_r_proto>

From F<d_getpwnam_r.U>:

This variable encodes the prototype of getpwnam_r.
It is zero if d_getpwnam_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getpwnam_r
is defined.

=item C<getpwuid_r_proto>

From F<d_getpwuid_r.U>:

This variable encodes the prototype of getpwuid_r.
It is zero if d_getpwuid_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getpwuid_r
is defined.

=item C<getservbyname_r_proto>

From F<d_getservbyname_r.U>:

This variable encodes the prototype of getservbyname_r.
It is zero if d_getservbyname_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getservbyname_r
is defined.

=item C<getservbyport_r_proto>

From F<d_getservbyport_r.U>:

This variable encodes the prototype of getservbyport_r.
It is zero if d_getservbyport_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getservbyport_r
is defined.

=item C<getservent_r_proto>

From F<d_getservent_r.U>:

This variable encodes the prototype of getservent_r.
It is zero if d_getservent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getservent_r
is defined.

=item C<getspnam_r_proto>

From F<d_getspnam_r.U>:

This variable encodes the prototype of getspnam_r.
It is zero if d_getspnam_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_getspnam_r
is defined.

=item C<gidformat>

From F<gidf.U>:

This variable contains the format string used for printing a Gid_t.

=item C<gidsign>

From F<gidsign.U>:

This variable contains the signedness of a gidtype.
1 for unsigned, -1 for signed.

=item C<gidsize>

From F<gidsize.U>:

This variable contains the size of a gidtype in bytes.

=item C<gidtype>

From F<gidtype.U>:

This variable defines Gid_t to be something like gid_t, int,
ushort, or whatever type is used to declare the return type
of getgid().  Typically, it is the type of group ids in the kernel.

=item C<glibpth>

From F<libpth.U>:

This variable holds the general path (space-separated) used to
find libraries.  It may contain directories that do not exist on
this platform, libpth is the cleaned-up version.

=item C<gmake>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the gmake program. After Configure runs,
the value is reset to a plain C<gmake> and is not useful.

=item C<gmtime_r_proto>

From F<d_gmtime_r.U>:

This variable encodes the prototype of gmtime_r.
It is zero if d_gmtime_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_gmtime_r
is defined.

=item C<gnulibc_version>

From F<d_gnulibc.U>:

This variable contains the version number of the C<GNU> C library.
It is usually something like F<2.2.5>. It is a plain '' if this
is not the C<GNU> C library, or if the version is unknown.

=item C<grep>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the grep program. After Configure runs,
the value is reset to a plain C<grep> and is not useful.

=item C<groupcat>

From F<nis.U>:

This variable contains a command that produces the text of the
F</etc/group> file. This is normally "cat F</etc/group>", but can be
"ypcat group" when C<NIS> is used.
On some systems, such as os390, there may be no equivalent
command, in which case this variable is unset.

=item C<groupstype>

From F<groupstype.U>:

This variable defines Groups_t to be something like gid_t, int,
ushort, or whatever type is used for the second argument to
getgroups() and setgroups().  Usually, this is the same as
gidtype (gid_t), but sometimes it isn't.

=item C<gzip>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the gzip program. After Configure runs,
the value is reset to a plain C<gzip> and is not useful.

=back

=head2 h

=over 4

=item C<h_fcntl>

From F<h_fcntl.U>:

This is variable gets set in various places to tell i_fcntl that
<fcntl.h> should be included.

=item C<h_sysfile>

From F<h_sysfile.U>:

This is variable gets set in various places to tell i_sys_file that
<sys/file.h> should be included.

=item C<hint>

From F<Oldconfig.U>:

Gives the type of hints used for previous answers. May be one of
C<default>, C<recommended> or C<previous>.

=item C<hostcat>

From F<nis.U>:

This variable contains a command that produces the text of the
F</etc/hosts> file. This is normally "cat F</etc/hosts>", but can be
"ypcat hosts" when C<NIS> is used.
On some systems, such as os390, there may be no equivalent
command, in which case this variable is unset.

=item C<hostgenerate>

From F<Cross.U>:

This variable contains the path to a generate_uudmap binary that
can be run on the host C<OS> when cross-compiling. Useful and
available only during Perl build.
Empty string '' if not cross-compiling.

=item C<hostosname>

From F<Cross.U>:

This variable contains the original value of C<$^O> for hostperl
when cross-compiling. This is useful to pick the proper tools
when running build code in the host.
Empty string '' if not cross-compiling.

=item C<hostperl>

From F<Cross.U>:

This variable contains the path to a miniperl binary that can be
run on the host C<OS> when cross-compiling. Useful and available only
during Perl build.
Empty string '' if not cross-compiling.

=item C<html1dir>

From F<html1dir.U>:

This variable contains the name of the directory in which html
source pages are to be put.  This directory is for pages
that describe whole programs, not libraries or modules.  It
is intended to correspond roughly to section 1 of the Unix
manuals.

=item C<html1direxp>

From F<html1dir.U>:

This variable is the same as the html1dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<html3dir>

From F<html3dir.U>:

This variable contains the name of the directory in which html
source pages are to be put.  This directory is for pages
that describe libraries or modules.  It is intended to
correspond roughly to section 3 of the Unix manuals.

=item C<html3direxp>

From F<html3dir.U>:

This variable is the same as the html3dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=back

=head2 i

=over 4

=item C<i16size>

From F<perlxv.U>:

This variable is the size of an I16 in bytes.

=item C<i16type>

From F<perlxv.U>:

This variable contains the C type used for Perl's I16.

=item C<i32size>

From F<perlxv.U>:

This variable is the size of an I32 in bytes.

=item C<i32type>

From F<perlxv.U>:

This variable contains the C type used for Perl's I32.

=item C<i64size>

From F<perlxv.U>:

This variable is the size of an I64 in bytes.

=item C<i64type>

From F<perlxv.U>:

This variable contains the C type used for Perl's I64.

=item C<i8size>

From F<perlxv.U>:

This variable is the size of an I8 in bytes.

=item C<i8type>

From F<perlxv.U>:

This variable contains the C type used for Perl's I8.

=item C<i_arpainet>

From F<i_arpainet.U>:

This variable conditionally defines the C<I_ARPA_INET> symbol,
and indicates whether a C program should include <arpa/inet.h>.

=item C<i_bfd>

From F<i_bfd.U>:

This variable conditionally defines the C<I_BFD> symbol, and
indicates whether a C program can include <bfd.h>.

=item C<i_bsdioctl>

From F<i_sysioctl.U>:

This variable conditionally defines the C<I_SYS_BSDIOCTL> symbol, which
indicates to the C program that <sys/bsdioctl.h> exists and should
be included.

=item C<i_crypt>

From F<i_crypt.U>:

This variable conditionally defines the C<I_CRYPT> symbol, and indicates
whether a C program should include <crypt.h>.

=item C<i_db>

From F<i_db.U>:

This variable conditionally defines the C<I_DB> symbol, and indicates
whether a C program may include Berkeley's C<DB> include file <db.h>.

=item C<i_dbm>

From F<i_dbm.U>:

This variable conditionally defines the C<I_DBM> symbol, which
indicates to the C program that <dbm.h> exists and should
be included.

=item C<i_dirent>

From F<i_dirent.U>:

This variable conditionally defines C<I_DIRENT>, which indicates
to the C program that it should include <dirent.h>.

=item C<i_dlfcn>

From F<i_dlfcn.U>:

This variable conditionally defines the C<I_DLFCN> symbol, which
indicates to the C program that <dlfcn.h> exists and should
be included.

=item C<i_execinfo>

From F<i_execinfo.U>:

This variable conditionally defines the C<I_EXECINFO> symbol, and indicates
whether a C program may include <execinfo.h>, for backtrace() support.

=item C<i_fcntl>

From F<i_fcntl.U>:

This variable controls the value of C<I_FCNTL> (which tells
the C program to include <fcntl.h>).

=item C<i_fenv>

From F<i_fenv.U>:

This variable conditionally defines the C<I_FENV> symbol, which
indicates to the C program that <fenv.h> exists and should
be included.

=item C<i_fp>

From F<i_fp.U>:

This variable conditionally defines the C<I_FP> symbol, and indicates
whether a C program should include <fp.h>.

=item C<i_fp_class>

From F<i_fp_class.U>:

This variable conditionally defines the C<I_FP_CLASS> symbol, and indicates
whether a C program should include <fp_class.h>.

=item C<i_gdbm>

From F<i_gdbm.U>:

This variable conditionally defines the C<I_GDBM> symbol, which
indicates to the C program that <gdbm.h> exists and should
be included.

=item C<i_gdbm_ndbm>

From F<i_ndbm.U>:

This variable conditionally defines the C<I_GDBM_NDBM> symbol, which
indicates to the C program that <gdbm-F<ndbm.h>> exists and should
be included. This is the location of the F<ndbm.h> compatibility file
in Debian 4.0.

=item C<i_gdbmndbm>

From F<i_ndbm.U>:

This variable conditionally defines the C<I_GDBMNDBM> symbol, which
indicates to the C program that <gdbm/ndbm.h> exists and should
be included. This was the location of the F<ndbm.h> compatibility file
in RedHat 7.1.

=item C<i_grp>

From F<i_grp.U>:

This variable conditionally defines the C<I_GRP> symbol, and indicates
whether a C program should include <grp.h>.

=item C<i_ieeefp>

From F<i_ieeefp.U>:

This variable conditionally defines the C<I_IEEEFP> symbol, and indicates
whether a C program should include <ieeefp.h>.

=item C<i_inttypes>

From F<i_inttypes.U>:

This variable conditionally defines the C<I_INTTYPES> symbol,
and indicates whether a C program should include <inttypes.h>.

=item C<i_langinfo>

From F<i_langinfo.U>:

This variable conditionally defines the C<I_LANGINFO> symbol,
and indicates whether a C program should include <langinfo.h>.

=item C<i_libutil>

From F<i_libutil.U>:

This variable conditionally defines the C<I_LIBUTIL> symbol, and indicates
whether a C program should include <libutil.h>.

=item C<i_locale>

From F<i_locale.U>:

This variable conditionally defines the C<I_LOCALE> symbol,
and indicates whether a C program should include <locale.h>.

=item C<i_machcthr>

From F<i_machcthr.U>:

This variable conditionally defines the C<I_MACH_CTHREADS> symbol,
and indicates whether a C program should include <mach/cthreads.h>.

=item C<i_malloc>

From F<i_malloc.U>:

This variable conditionally defines the C<I_MALLOC> symbol, and indicates
whether a C program should include <malloc.h>.

=item C<i_mallocmalloc>

From F<i_mallocmalloc.U>:

This variable conditionally defines the C<I_MALLOCMALLOC> symbol,
and indicates whether a C program should include <malloc/malloc.h>.

=item C<i_mntent>

From F<i_mntent.U>:

This variable conditionally defines the C<I_MNTENT> symbol, and indicates
whether a C program should include <mntent.h>.

=item C<i_ndbm>

From F<i_ndbm.U>:

This variable conditionally defines the C<I_NDBM> symbol, which
indicates to the C program that <ndbm.h> exists and should
be included.

=item C<i_netdb>

From F<i_netdb.U>:

This variable conditionally defines the C<I_NETDB> symbol, and indicates
whether a C program should include <netdb.h>.

=item C<i_neterrno>

From F<i_neterrno.U>:

This variable conditionally defines the C<I_NET_ERRNO> symbol, which
indicates to the C program that <net/errno.h> exists and should
be included.

=item C<i_netinettcp>

From F<i_netinettcp.U>:

This variable conditionally defines the C<I_NETINET_TCP> symbol,
and indicates whether a C program should include <netinet/tcp.h>.

=item C<i_niin>

From F<i_niin.U>:

This variable conditionally defines C<I_NETINET_IN>, which indicates
to the C program that it should include <netinet/in.h>. Otherwise,
you may try <sys/in.h>.

=item C<i_poll>

From F<i_poll.U>:

This variable conditionally defines the C<I_POLL> symbol, and indicates
whether a C program should include <poll.h>.

=item C<i_prot>

From F<i_prot.U>:

This variable conditionally defines the C<I_PROT> symbol, and indicates
whether a C program should include <prot.h>.

=item C<i_pthread>

From F<i_pthread.U>:

This variable conditionally defines the C<I_PTHREAD> symbol,
and indicates whether a C program should include <pthread.h>.

=item C<i_pwd>

From F<i_pwd.U>:

This variable conditionally defines C<I_PWD>, which indicates
to the C program that it should include <pwd.h>.

=item C<i_quadmath>

From F<i_quadmath.U>:

This variable conditionally defines C<I_QUADMATH>, which indicates
to the C program that it should include <quadmath.h>.

=item C<i_rpcsvcdbm>

From F<i_dbm.U>:

This variable conditionally defines the C<I_RPCSVC_DBM> symbol, which
indicates to the C program that <rpcsvc/dbm.h> exists and should
be included. Some System V systems might need this instead of <dbm.h>.

=item C<i_sgtty>

From F<i_termio.U>:

This variable conditionally defines the C<I_SGTTY> symbol, which
indicates to the C program that it should include <sgtty.h> rather
than <termio.h>.

=item C<i_shadow>

From F<i_shadow.U>:

This variable conditionally defines the C<I_SHADOW> symbol, and indicates
whether a C program should include <shadow.h>.

=item C<i_socks>

From F<i_socks.U>:

This variable conditionally defines the C<I_SOCKS> symbol, and indicates
whether a C program should include <socks.h>.

=item C<i_stdbool>

From F<i_stdbool.U>:

This variable conditionally defines the C<I_STDBOOL> symbol, which
indicates to the C program that <stdbool.h> exists and should
be included.

=item C<i_stdint>

From F<i_stdint.U>:

This variable conditionally defines the C<I_STDINT> symbol, which
indicates to the C program that <stdint.h> exists and should
be included.

=item C<i_stdlib>

From F<i_stdlib.U>:

This variable unconditionally defines the C<I_STDLIB> symbol.

=item C<i_sunmath>

From F<i_sunmath.U>:

This variable conditionally defines the C<I_SUNMATH> symbol, and indicates
whether a C program should include <sunmath.h>.

=item C<i_sysaccess>

From F<i_sysaccess.U>:

This variable conditionally defines the C<I_SYS_ACCESS> symbol,
and indicates whether a C program should include <sys/access.h>.

=item C<i_sysdir>

From F<i_sysdir.U>:

This variable conditionally defines the C<I_SYS_DIR> symbol, and indicates
whether a C program should include <sys/dir.h>.

=item C<i_sysfile>

From F<i_sysfile.U>:

This variable conditionally defines the C<I_SYS_FILE> symbol, and indicates
whether a C program should include <sys/file.h> to get C<R_OK> and friends.

=item C<i_sysfilio>

From F<i_sysioctl.U>:

This variable conditionally defines the C<I_SYS_FILIO> symbol, which
indicates to the C program that <sys/filio.h> exists and should
be included in preference to <sys/ioctl.h>.

=item C<i_sysin>

From F<i_niin.U>:

This variable conditionally defines C<I_SYS_IN>, which indicates
to the C program that it should include <sys/in.h> instead of
<netinet/in.h>.

=item C<i_sysioctl>

From F<i_sysioctl.U>:

This variable conditionally defines the C<I_SYS_IOCTL> symbol, which
indicates to the C program that <sys/ioctl.h> exists and should
be included.

=item C<i_syslog>

From F<i_syslog.U>:

This variable conditionally defines the C<I_SYSLOG> symbol,
and indicates whether a C program should include <syslog.h>.

=item C<i_sysmman>

From F<i_sysmman.U>:

This variable conditionally defines the C<I_SYS_MMAN> symbol,
and indicates whether a C program should include <sys/mman.h>.

=item C<i_sysmode>

From F<i_sysmode.U>:

This variable conditionally defines the C<I_SYSMODE> symbol,
and indicates whether a C program should include <sys/mode.h>.

=item C<i_sysmount>

From F<i_sysmount.U>:

This variable conditionally defines the C<I_SYSMOUNT> symbol,
and indicates whether a C program should include <sys/mount.h>.

=item C<i_sysndir>

From F<i_sysndir.U>:

This variable conditionally defines the C<I_SYS_NDIR> symbol, and indicates
whether a C program should include <sys/ndir.h>.

=item C<i_sysparam>

From F<i_sysparam.U>:

This variable conditionally defines the C<I_SYS_PARAM> symbol, and indicates
whether a C program should include <sys/param.h>.

=item C<i_syspoll>

From F<i_syspoll.U>:

This variable conditionally defines the C<I_SYS_POLL> symbol, which
indicates to the C program that it should include <sys/poll.h>.

=item C<i_sysresrc>

From F<i_sysresrc.U>:

This variable conditionally defines the C<I_SYS_RESOURCE> symbol,
and indicates whether a C program should include <sys/resource.h>.

=item C<i_syssecrt>

From F<i_syssecrt.U>:

This variable conditionally defines the C<I_SYS_SECURITY> symbol,
and indicates whether a C program should include <sys/security.h>.

=item C<i_sysselct>

From F<i_sysselct.U>:

This variable conditionally defines C<I_SYS_SELECT>, which indicates
to the C program that it should include <sys/select.h> in order to
get the definition of struct timeval.

=item C<i_syssockio>

From F<i_sysioctl.U>:

This variable conditionally defines C<I_SYS_SOCKIO> to indicate to the
C program that socket ioctl codes may be found in <sys/sockio.h>
instead of <sys/ioctl.h>.

=item C<i_sysstat>

From F<i_sysstat.U>:

This variable conditionally defines the C<I_SYS_STAT> symbol,
and indicates whether a C program should include <sys/stat.h>.

=item C<i_sysstatfs>

From F<i_sysstatfs.U>:

This variable conditionally defines the C<I_SYSSTATFS> symbol,
and indicates whether a C program should include <sys/statfs.h>.

=item C<i_sysstatvfs>

From F<i_sysstatvfs.U>:

This variable conditionally defines the C<I_SYSSTATVFS> symbol,
and indicates whether a C program should include <sys/statvfs.h>.

=item C<i_systime>

From F<i_time.U>:

This variable conditionally defines C<I_SYS_TIME>, which indicates
to the C program that it should include <sys/time.h>.

=item C<i_systimek>

From F<i_time.U>:

This variable conditionally defines C<I_SYS_TIME_KERNEL>, which
indicates to the C program that it should include <sys/time.h>
with C<KERNEL> defined.

=item C<i_systimes>

From F<i_systimes.U>:

This variable conditionally defines the C<I_SYS_TIMES> symbol, and indicates
whether a C program should include <sys/times.h>.

=item C<i_systypes>

From F<i_systypes.U>:

This variable conditionally defines the C<I_SYS_TYPES> symbol,
and indicates whether a C program should include <sys/types.h>.

=item C<i_sysuio>

From F<i_sysuio.U>:

This variable conditionally defines the C<I_SYSUIO> symbol, and indicates
whether a C program should include <sys/uio.h>.

=item C<i_sysun>

From F<i_sysun.U>:

This variable conditionally defines C<I_SYS_UN>, which indicates
to the C program that it should include <sys/un.h> to get C<UNIX>
domain socket definitions.

=item C<i_sysutsname>

From F<i_sysutsname.U>:

This variable conditionally defines the C<I_SYSUTSNAME> symbol,
and indicates whether a C program should include <sys/utsname.h>.

=item C<i_sysvfs>

From F<i_sysvfs.U>:

This variable conditionally defines the C<I_SYSVFS> symbol,
and indicates whether a C program should include <sys/vfs.h>.

=item C<i_syswait>

From F<i_syswait.U>:

This variable conditionally defines C<I_SYS_WAIT>, which indicates
to the C program that it should include <sys/wait.h>.

=item C<i_termio>

From F<i_termio.U>:

This variable conditionally defines the C<I_TERMIO> symbol, which
indicates to the C program that it should include <termio.h> rather
than <sgtty.h>.

=item C<i_termios>

From F<i_termio.U>:

This variable conditionally defines the C<I_TERMIOS> symbol, which
indicates to the C program that the C<POSIX> <termios.h> file is
to be included.

=item C<i_time>

From F<i_time.U>:

This variable unconditionally defines C<I_TIME>, which indicates
to the C program that it should include <time.h>.

=item C<i_unistd>

From F<i_unistd.U>:

This variable conditionally defines the C<I_UNISTD> symbol, and indicates
whether a C program should include <unistd.h>.

=item C<i_ustat>

From F<i_ustat.U>:

This variable conditionally defines the C<I_USTAT> symbol, and indicates
whether a C program should include <ustat.h>.

=item C<i_utime>

From F<i_utime.U>:

This variable conditionally defines the C<I_UTIME> symbol, and indicates
whether a C program should include <utime.h>.

=item C<i_vfork>

From F<i_vfork.U>:

This variable conditionally defines the C<I_VFORK> symbol, and indicates
whether a C program should include F<vfork.h>.

=item C<i_wchar>

From F<i_wchar.U>:

This variable conditionally defines the C<I_WCHAR> symbol,
that indicates whether a C program may include <wchar.h>.

=item C<i_wctype>

From F<i_wctype.U>:

This variable conditionally defines the C<I_WCTYPE> symbol,
that indicates whether a C program may include <wctype.h>.

=item C<i_xlocale>

From F<d_newlocale.U>:

This symbol, if defined, indicates to the C program that it should
include <xlocale.h> to get uselocale() and its friends

=item C<ignore_versioned_solibs>

From F<libs.U>:

This variable should be non-empty if non-versioned shared
libraries (F<libfoo.so.x.y>) are to be ignored (because they
cannot be linked against).

=item C<inc_version_list>

From F<inc_version_list.U>:

This variable specifies the list of subdirectories in over
which F<perl.c>:incpush() and F<lib/lib.pm> will automatically
search when adding directories to @C<INC>. The elements in
the list are separated by spaces. This is only useful
if you have a perl library directory tree structured like the
default one. See C<INSTALL> for how this works. The versioned
site_perl directory was introduced in 5.005, so that is the
lowest possible value.

This list includes architecture-dependent directories back to
version $api_versionstring (e.g. 5.5.640) and
architecture-independent directories all the way back to
5.005.

=item C<inc_version_list_init>

From F<inc_version_list.U>:

This variable holds the same list as inc_version_list, but
each item is enclosed in double quotes and separated by commas,
suitable for use in the C<PERL_INC_VERSION_LIST> initialization.

=item C<incpath>

From F<usrinc.U>:

This variable must precede the normal include path to get the
right one, as in F<$incpath/usr/include> or F<$incpath/usr/lib>.
Value can be "" or F</bsd43> on mips.

=item C<incpth>

From F<libpth.U>:

This variable must precede the normal include path to get the
right one, as in F<$incpath/usr/include> or F<$incpath/usr/lib>.
Value can be "" or F</bsd43> on mips.

=item C<inews>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<initialinstalllocation>

From F<bin.U>:

When userelocatableinc is true, this variable holds the location
that make install should copy the perl binary to, with all the
run-time relocatable paths calculated from this at install time.
When used, it is initialized to the original value of binexp, and
then binexp is set to F<.../>, as the other binaries are found
relative to the perl binary.

=item C<installarchlib>

From F<archlib.U>:

This variable is really the same as archlibexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installbin>

From F<bin.U>:

This variable is the same as binexp unless C<AFS> is running in which case
the user is explicitly prompted for it. This variable should always
be used in your makefiles for maximum portability.

=item C<installhtml1dir>

From F<html1dir.U>:

This variable is really the same as html1direxp, unless you are
using a different installprefix.  For extra portability, you
should only use this variable within your makefiles.

=item C<installhtml3dir>

From F<html3dir.U>:

This variable is really the same as html3direxp, unless you are
using a different installprefix.  For extra portability, you
should only use this variable within your makefiles.

=item C<installman1dir>

From F<man1dir.U>:

This variable is really the same as man1direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
man1direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installman3dir>

From F<man3dir.U>:

This variable is really the same as man3direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
man3direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installprefix>

From F<installprefix.U>:

This variable holds the name of the directory below which
"make install" will install the package.  For most users, this
is the same as prefix.  However, it is useful for
installing the software into a different (usually temporary)
location after which it can be bundled up and moved somehow
to the final location specified by prefix.

=item C<installprefixexp>

From F<installprefix.U>:

This variable holds the full absolute path of installprefix
with all F<~>-expansion done.

=item C<installprivlib>

From F<privlib.U>:

This variable is really the same as privlibexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installscript>

From F<scriptdir.U>:

This variable is usually the same as scriptdirexp, unless you are on
a system running C<AFS>, in which case they may differ slightly. You
should always use this variable within your makefiles for portability.

=item C<installsitearch>

From F<sitearch.U>:

This variable is really the same as sitearchexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installsitebin>

From F<sitebin.U>:

This variable is usually the same as sitebinexp, unless you are on
a system running C<AFS>, in which case they may differ slightly. You
should always use this variable within your makefiles for portability.

=item C<installsitehtml1dir>

From F<sitehtml1dir.U>:

This variable is really the same as sitehtml1direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
html1direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installsitehtml3dir>

From F<sitehtml3dir.U>:

This variable is really the same as sitehtml3direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
html3direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installsitelib>

From F<sitelib.U>:

This variable is really the same as sitelibexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installsiteman1dir>

From F<siteman1dir.U>:

This variable is really the same as siteman1direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
man1direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installsiteman3dir>

From F<siteman3dir.U>:

This variable is really the same as siteman3direxp, unless you are using
C<AFS> in which case it points to the read/write location whereas
man3direxp only points to the read-only access location. For extra
portability, you should only use this variable within your makefiles.

=item C<installsitescript>

From F<sitescript.U>:

This variable is usually the same as sitescriptexp, unless you are on
a system running C<AFS>, in which case they may differ slightly. You
should always use this variable within your makefiles for portability.

=item C<installstyle>

From F<installstyle.U>:

This variable describes the C<style> of the perl installation.
This is intended to be useful for tools that need to
manipulate entire perl distributions. Perl itself doesn't use
this to find its libraries -- the library directories are
stored directly in F<Config.pm>. Currently, there are only two
styles: C<lib> and F<lib/perl5>. The default library locations
(e.g. privlib, sitelib) are either F<$prefix/lib> or
F<$prefix/lib/perl5>. The former is useful if $prefix is a
directory dedicated to perl (e.g. F</opt/perl>), while the latter
is useful if $prefix is shared by many packages, e.g. if
$prefix=F</usr/local>.

Unfortunately, while this C<style> variable is used to set
defaults for all three directory hierarchies (core, vendor, and
site), there is no guarantee that the same style is actually
appropriate for all those directories. For example, $prefix
might be F</opt/perl>, but $siteprefix might be F</usr/local>.
(Perhaps, in retrospect, the C<lib> style should never have been
supported, but it did seem like a nice idea at the time.)

The situation is even less clear for tools such as MakeMaker
that can be used to install additional modules into
non-standard places. For example, if a user intends to install
a module into a private directory (perhaps by setting C<PREFIX> on
the F<Makefile.PL> command line), then there is no reason to
assume that the Configure-time $installstyle setting will be
relevant for that C<PREFIX>.

This may later be extended to include other information, so
be careful with pattern-matching on the results.

For compatibility with F<perl5.005> and earlier, the default
setting is based on whether or not $prefix contains the string
C<perl>.

=item C<installusrbinperl>

From F<instubperl.U>:

This variable tells whether Perl should be installed also as
F</usr/bin/perl> in addition to
F<$installbin/perl>

=item C<installvendorarch>

From F<vendorarch.U>:

This variable is really the same as vendorarchexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorbin>

From F<vendorbin.U>:

This variable is really the same as vendorbinexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorhtml1dir>

From F<vendorhtml1dir.U>:

This variable is really the same as vendorhtml1direxp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorhtml3dir>

From F<vendorhtml3dir.U>:

This variable is really the same as vendorhtml3direxp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorlib>

From F<vendorlib.U>:

This variable is really the same as vendorlibexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorman1dir>

From F<vendorman1dir.U>:

This variable is really the same as vendorman1direxp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorman3dir>

From F<vendorman3dir.U>:

This variable is really the same as vendorman3direxp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<installvendorscript>

From F<vendorscript.U>:

This variable is really the same as vendorscriptexp but may differ on
those systems using C<AFS>. For extra portability, only this variable
should be used in makefiles.

=item C<intsize>

From F<intsize.U>:

This variable contains the value of the C<INTSIZE> symbol, which
indicates to the C program how many bytes there are in an int.

=item C<issymlink>

From F<issymlink.U>:

This variable holds the test command to test for a symbolic link
(if they are supported). Typical values include C<test -h> and
C<test -L>.

=item C<ivdformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<IV> as a signed decimal integer.

=item C<ivsize>

From F<perlxv.U>:

This variable is the size of an C<IV> in bytes.

=item C<ivtype>

From F<perlxv.U>:

This variable contains the C type used for Perl's C<IV>.

=back

=head2 k

=over 4

=item C<known_extensions>

From F<Extensions.U>:

This variable holds a list of all extensions (both C<XS> and non-xs)
included in the package source distribution. This information is
only really of use during the Perl build, as the list makes no
distinction between extensions which were build and installed, and
those which where not. See C<extensions> for the list of extensions
actually built and available.

=item C<ksh>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=back

=head2 l

=over 4

=item C<ld>

From F<dlsrc.U>:

This variable indicates the program to be used to link
libraries for dynamic loading. On some systems, it is C<ld>.
On C<ELF> systems, it should be $cc. Mostly, we'll try to respect
the hint file setting.

=item C<ld_can_script>

From F<dlsrc.U>:

This variable shows if the loader accepts scripts in the form of
-Wl,--version-script=F<ld.script>. This is currently only supported
for C<GNU> ld on C<ELF> in dynamic loading builds.

=item C<lddlflags>

From F<dlsrc.U>:

This variable contains any special flags that might need to be
passed to $ld to create a shared library suitable for dynamic
loading. It is up to the makefile to use it. For hpux, it
should be C<-b>. For sunos 4.1, it is empty.

=item C<ldflags>

From F<ccflags.U>:

This variable contains any additional C loader flags desired by
the user.  It is up to the Makefile to use this.

=item C<ldflags_uselargefiles>

From F<uselfs.U>:

This variable contains the loader flags needed by large file builds
and added to ldflags by hints files.

=item C<ldlibpthname>

From F<libperl.U>:

This variable holds the name of the shared library
search path, often C<LD_LIBRARY_PATH>. To get an empty
string, the hints file must set this to C<none>.

=item C<less>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the less program. After Configure runs,
the value is reset to a plain C<less> and is not useful.

=item C<lib_ext>

From F<Unix.U>:

This is an old synonym for _a.

=item C<libc>

From F<libc.U>:

This variable contains the location of the C library.

=item C<libperl>

From F<libperl.U>:

The perl executable is obtained by linking F<perlmain.c> with
libperl, any static extensions (usually just DynaLoader),
and any other libraries needed on this system. libperl
is usually F<libperl.a>, but can also be F<libperl.so.xxx> if
the user wishes to build a perl executable with a shared
library.

=item C<libpth>

From F<libpth.U>:

This variable holds the general path (space-separated) used to find
libraries. It is intended to be used by other units.

=item C<libs>

From F<libs.U>:

This variable holds the additional libraries we want to use.
It is up to the Makefile to deal with it.  The list can be empty.

=item C<libsdirs>

From F<libs.U>:

This variable holds the directory names aka dirnames of the libraries
we found and accepted, duplicates are removed.

=item C<libsfiles>

From F<libs.U>:

This variable holds the filenames aka basenames of the libraries
we found and accepted.

=item C<libsfound>

From F<libs.U>:

This variable holds the full pathnames of the libraries
we found and accepted.

=item C<libspath>

From F<libs.U>:

This variable holds the directory names probed for libraries.

=item C<libswanted>

From F<Myinit.U>:

This variable holds a list of all the libraries we want to
search.  The order is chosen to pick up the c library
ahead of ucb or bsd libraries for SVR4.

=item C<libswanted_uselargefiles>

From F<uselfs.U>:

This variable contains the libraries needed by large file builds
and added to ldflags by hints files. It is a space separated list
of the library names without the C<lib> prefix or any suffix, just
like F<libswanted.>.

=item C<line>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<lint>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<lkflags>

From F<ccflags.U>:

This variable contains any additional C partial linker flags desired by
the user.  It is up to the Makefile to use this.

=item C<ln>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the ln program. After Configure runs,
the value is reset to a plain C<ln> and is not useful.

=item C<lns>

From F<lns.U>:

This variable holds the name of the command to make
symbolic links (if they are supported). It can be used
in the Makefile. It is either C<ln -s> or C<ln>

=item C<localtime_r_proto>

From F<d_localtime_r.U>:

This variable encodes the prototype of localtime_r.
It is zero if d_localtime_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_localtime_r
is defined.

=item C<locincpth>

From F<ccflags.U>:

This variable contains a list of additional directories to be
searched by the compiler. The appropriate C<-I> directives will
be added to ccflags. This is intended to simplify setting
local directories from the Configure command line.
It's not much, but it parallels the loclibpth stuff in F<libpth.U>.

=item C<loclibpth>

From F<libpth.U>:

This variable holds the paths (space-separated) used to find local
libraries.  It is prepended to libpth, and is intended to be easily
set from the command line.

=item C<longdblinfbytes>

From F<infnan.U>:

This variable contains comma-separated list of hexadecimal bytes
for the long double precision infinity.

=item C<longdblkind>

From F<d_longdbl.U>:

This variable, if defined, encodes the type of a long double:
0 = double,
1 = C<IEEE> 754 128-bit little endian,
2 = C<IEEE> 754 128-bit big endian,
3 = x86 80-bit little endian,
4 = x86 80-bit big endian,
5 = double-double 128-bit little endian,
6 = double-double 128-bit big endian,
7 = 128-bit mixed-endian double-double (64-bit LEs in C<BE>),
8 = 128-bit mixed-endian double-double (64-bit BEs in C<LE>),
9 = 128-bit C<PDP>-style mixed-endian long doubles,
-1 = unknown format.

=item C<longdblmantbits>

From F<mantbits.U>:

This symbol, if defined, tells how many mantissa bits
there are in long double precision floating point format.
Note that this can be C<LDBL_MANT_DIG> minus one,
since C<LDBL_MANT_DIG> can include the C<IEEE> 754 implicit bit.
The common x86-style 80-bit long double does not have
an implicit bit.

=item C<longdblnanbytes>

From F<infnan.U>:

This variable contains comma-separated list of hexadecimal bytes
for the long double precision not-a-number.

=item C<longdblsize>

From F<d_longdbl.U>:

This variable contains the value of the C<LONG_DOUBLESIZE> symbol, which
indicates to the C program how many bytes there are in a long double,
if this system supports long doubles. Note that this is
sizeof(long double), which may include unused bytes.

=item C<longlongsize>

From F<d_longlong.U>:

This variable contains the value of the C<LONGLONGSIZE> symbol, which
indicates to the C program how many bytes there are in a long long,
if this system supports long long.

=item C<longsize>

From F<intsize.U>:

This variable contains the value of the C<LONGSIZE> symbol, which
indicates to the C program how many bytes there are in a long.

=item C<lp>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<lpr>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<ls>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the ls program. After Configure runs,
the value is reset to a plain C<ls> and is not useful.

=item C<lseeksize>

From F<lseektype.U>:

This variable defines lseektype to be something like off_t, long,
or whatever type is used to declare lseek offset's type in the
kernel (which also appears to be lseek's return type).

=item C<lseektype>

From F<lseektype.U>:

This variable defines lseektype to be something like off_t, long,
or whatever type is used to declare lseek offset's type in the
kernel (which also appears to be lseek's return type).

=back

=head2 m

=over 4

=item C<mail>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<mailx>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<make>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the make program. After Configure runs,
the value is reset to a plain C<make> and is not useful.

=item C<make_set_make>

From F<make.U>:

Some versions of C<make> set the variable C<MAKE>. Others do not.
This variable contains the string to be included in F<Makefile.SH>
so that C<MAKE> is set if needed, and not if not needed.
Possible values are:

make_set_make=C<#>		# If your make program handles this for you,

make_set_make=C<MAKE=$make>	# if it doesn't.

This uses a comment character so that we can distinguish a
C<set> value (from a previous F<config.sh> or Configure C<-D> option)
from an uncomputed value.

=item C<mallocobj>

From F<mallocsrc.U>:

This variable contains the name of the F<malloc.o> that this package
generates, if that F<malloc.o> is preferred over the system malloc.
Otherwise the value is null. This variable is intended for generating
Makefiles. See mallocsrc.

=item C<mallocsrc>

From F<mallocsrc.U>:

This variable contains the name of the F<malloc.c> that comes with
the package, if that F<malloc.c> is preferred over the system malloc.
Otherwise the value is null. This variable is intended for generating
Makefiles.

=item C<malloctype>

From F<mallocsrc.U>:

This variable contains the kind of ptr returned by malloc and realloc.

=item C<man1dir>

From F<man1dir.U>:

This variable contains the name of the directory in which manual
source pages are to be put. It is the responsibility of the
F<Makefile.SH> to get the value of this into the proper command.
You must be prepared to do the F<~name> expansion yourself.

=item C<man1direxp>

From F<man1dir.U>:

This variable is the same as the man1dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<man1ext>

From F<man1dir.U>:

This variable contains the extension that the manual page should
have: one of C<n>, C<l>, or C<1>. The Makefile must supply the F<.>.
See man1dir.

=item C<man3dir>

From F<man3dir.U>:

=item C<man3direxp>

From F<man3dir.U>:

This variable is the same as the man3dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<man3ext>

From F<man3dir.U>:

This variable contains the extension that the manual page should
have: one of C<n>, C<l>, or C<3>. The Makefile must supply the F<.>.
See man3dir.

=item C<mips_type>

From F<usrinc.U>:

This variable holds the environment type for the mips system.
Possible values are "BSD 4.3" and "System V".

=item C<mistrustnm>

From F<Csym.U>:

This variable can be used to establish a fallthrough for the cases
where nm fails to find a symbol. If usenm is false or usenm is true
and mistrustnm is false, this variable has no effect. If usenm is true
and mistrustnm is C<compile>, a test program will be compiled to try to
find any symbol that can't be located via nm lookup. If mistrustnm is
C<run>, the test program will be run as well as being compiled.

=item C<mkdir>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the mkdir program. After Configure runs,
the value is reset to a plain C<mkdir> and is not useful.

=item C<mmaptype>

From F<d_mmap.U>:

This symbol contains the type of pointer returned by mmap()
(and simultaneously the type of the first argument).
It can be C<void *> or C<caddr_t>.

=item C<modetype>

From F<modetype.U>:

This variable defines modetype to be something like mode_t,
int, unsigned short, or whatever type is used to declare file
modes for system calls.

=item C<more>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the more program. After Configure runs,
the value is reset to a plain C<more> and is not useful.

=item C<multiarch>

From F<multiarch.U>:

This variable conditionally defines the C<MULTIARCH> symbol
which signifies the presence of multiplatform files.
This is normally set by hints files.

=item C<mv>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<myarchname>

From F<archname.U>:

This variable holds the architecture name computed by Configure in
a previous run. It is not intended to be perused by any user and
should never be set in a hint file.

=item C<mydomain>

From F<myhostname.U>:

This variable contains the eventual value of the C<MYDOMAIN> symbol,
which is the domain of the host the program is going to run on.
The domain must be appended to myhostname to form a complete host name.
The dot comes with mydomain, and need not be supplied by the program.

=item C<myhostname>

From F<myhostname.U>:

This variable contains the eventual value of the C<MYHOSTNAME> symbol,
which is the name of the host the program is going to run on.
The domain is not kept with hostname, but must be gotten from mydomain.
The dot comes with mydomain, and need not be supplied by the program.

=item C<myuname>

From F<Oldconfig.U>:

The output of C<uname -a> if available, otherwise the hostname.
The whole thing is then lower-cased and slashes and single quotes are
removed.

=back

=head2 n

=over 4

=item C<n>

From F<n.U>:

This variable contains the C<-n> flag if that is what causes the echo
command to suppress newline. Otherwise it is null. Correct usage is
$echo $n "prompt for a question: $c".

=item C<need_va_copy>

From F<need_va_copy.U>:

This symbol, if defined, indicates that the system stores
the variable argument list datatype, va_list, in a format
that cannot be copied by simple assignment, so that some
other means must be used when copying is required.
As such systems vary in their provision (or non-provision)
of copying mechanisms, F<handy.h> defines a platform-
C<independent> macro, Perl_va_copy(src, dst), to do the job.

=item C<netdb_hlen_type>

From F<netdbtype.U>:

This variable holds the type used for the 2nd argument to
gethostbyaddr().  Usually, this is int or size_t or unsigned.
This is only useful if you have gethostbyaddr(), naturally.

=item C<netdb_host_type>

From F<netdbtype.U>:

This variable holds the type used for the 1st argument to
gethostbyaddr().  Usually, this is char * or void *,  possibly
with or without a const prefix.
This is only useful if you have gethostbyaddr(), naturally.

=item C<netdb_name_type>

From F<netdbtype.U>:

This variable holds the type used for the argument to
gethostbyname().  Usually, this is char * or const char *.
This is only useful if you have gethostbyname(), naturally.

=item C<netdb_net_type>

From F<netdbtype.U>:

This variable holds the type used for the 1st argument to
getnetbyaddr().  Usually, this is int or long.
This is only useful if you have getnetbyaddr(), naturally.

=item C<nm>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the nm program. After Configure runs,
the value is reset to a plain C<nm> and is not useful.

=item C<nm_opt>

From F<usenm.U>:

This variable holds the options that may be necessary for nm.

=item C<nm_so_opt>

From F<usenm.U>:

This variable holds the options that may be necessary for nm
to work on a shared library but that can not be used on an
archive library. Currently, this is only used by Linux, where
nm --dynamic is *required* to get symbols from an C<ELF> library which
has been stripped, but nm --dynamic is *fatal* on an archive library.
Maybe Linux should just always set usenm=false.

=item C<nonxs_ext>

From F<Extensions.U>:

This variable holds a list of all non-xs extensions built and
installed by the package. By default, all non-xs extensions
distributed will be built, with the exception of platform-specific
extensions (currently only one C<VMS> specific extension).

=item C<nroff>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the nroff program. After Configure runs,
the value is reset to a plain C<nroff> and is not useful.

=item C<nv_overflows_integers_at>

From F<perlxv.U>:

This variable gives the largest integer value that NVs can hold
as a constant floating point expression.
If it could not be determined, it holds the value 0.

=item C<nv_preserves_uv_bits>

From F<perlxv.U>:

This variable indicates how many of bits type uvtype
a variable nvtype can preserve.

=item C<nveformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %e-ish floating point format.

=item C<nvEUformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %E-ish floating point format.

=item C<nvfformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %f-ish floating point format.

=item C<nvFUformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %F-ish floating point format.

=item C<nvgformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %g-ish floating point format.

=item C<nvGUformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<NV> using %G-ish floating point format.

=item C<nvmantbits>

From F<mantbits.U>:

This variable tells how many bits the mantissa of a Perl C<NV> has,
not including the possible implicit bit.

=item C<nvsize>

From F<perlxv.U>:

This variable is the size of a Perl C<NV> in bytes.
Note that some floating point formats have unused bytes.

=item C<nvtype>

From F<perlxv.U>:

This variable contains the C type used for Perl's C<NV>.

=back

=head2 o

=over 4

=item C<o_nonblock>

From F<nblock_io.U>:

This variable bears the symbol value to be used during open() or fcntl()
to turn on non-blocking I/O for a file descriptor. If you wish to switch
between blocking and non-blocking, you may try ioctl(C<FIOSNBIO>) instead,
but that is only supported by some devices.

=item C<obj_ext>

From F<Unix.U>:

This is an old synonym for _o.

=item C<old_pthread_create_joinable>

From F<d_pthrattrj.U>:

This variable defines the constant to use for creating joinable
(aka undetached) pthreads. Unused if F<pthread.h> defines
C<PTHREAD_CREATE_JOINABLE>. If used, possible values are
C<PTHREAD_CREATE_UNDETACHED> and C<__UNDETACHED>.

=item C<optimize>

From F<ccflags.U>:

This variable contains any F<optimizer/debugger> flag that should be used.
It is up to the Makefile to use it.

=item C<orderlib>

From F<orderlib.U>:

This variable is C<true> if the components of libraries must be ordered
(with `lorder $* | tsort`) before placing them in an archive. Set to
C<false> if ranlib or ar can generate random libraries.

=item C<osname>

From F<Oldconfig.U>:

This variable contains the operating system name (e.g. sunos,
solaris, hpux, etc.).  It can be useful later on for setting
defaults.  Any spaces are replaced with underscores.  It is set
to a null string if we can't figure it out.

=item C<osvers>

From F<Oldconfig.U>:

This variable contains the operating system version (e.g.
4.1.3, 5.2, etc.). It is primarily used for helping select
an appropriate hints file, but might be useful elsewhere for
setting defaults. It is set to '' if we can't figure it out.
We try to be flexible about how much of the version number
to keep, e.g. if 4.1.1, 4.1.2, and 4.1.3 are essentially the
same for this package, hints files might just be F<os_4.0> or
F<os_4.1>, etc., not keeping separate files for each little release.

=item C<otherlibdirs>

From F<otherlibdirs.U>:

This variable contains a colon-separated set of paths for the perl
binary to search for additional library files or modules.
These directories will be tacked to the end of @C<INC>.
Perl will automatically search below each path for version-
and architecture-specific directories. See inc_version_list
for more details.
A value of C< > means C<none> and is used to preserve this value
for the next run through Configure.

=back

=head2 p

=over 4

=item C<package>

From F<package.U>:

This variable contains the name of the package being constructed.
It is primarily intended for the use of later Configure units.

=item C<pager>

From F<pager.U>:

This variable contains the name of the preferred pager on the system.
Usual values are (the full pathnames of) more, less, pg, or cat.

=item C<passcat>

From F<nis.U>:

This variable contains a command that produces the text of the
F</etc/passwd> file. This is normally "cat F</etc/passwd>", but can be
"ypcat passwd" when C<NIS> is used.
On some systems, such as os390, there may be no equivalent
command, in which case this variable is unset.

=item C<patchlevel>

From F<patchlevel.U>:

The patchlevel level of this package.
The value of patchlevel comes from the F<patchlevel.h> file.
In a version number such as 5.6.1, this is the C<6>.
In F<patchlevel.h>, this is referred to as C<PERL_VERSION>.

=item C<path_sep>

From F<Unix.U>:

This is an old synonym for p_ in F<Head.U>, the character
used to separate elements in the command shell search C<PATH>.

=item C<perl>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the perl program. After Configure runs,
the value is reset to a plain C<perl> and is not useful.

=item C<perl5>

From F<perl5.U>:

This variable contains the full path (if any) to a previously
installed F<perl5.005> or later suitable for running the script
to determine inc_version_list.

=back

=head2 P

=over 4

=item C<PERL_API_REVISION>

From F<patchlevel.h>:

This number describes the earliest compatible C<PERL_REVISION> of
Perl (C<compatibility> here being defined as sufficient F<binary/C<API>>
compatibility to run C<XS> code built with the older version).
Normally this does not change across maintenance releases.
Please read the comment in F<patchlevel.h>.

=item C<PERL_API_SUBVERSION>

From F<patchlevel.h>:

This number describes the earliest compatible C<PERL_SUBVERSION> of
Perl (C<compatibility> here being defined as sufficient F<binary/C<API>>
compatibility to run C<XS> code built with the older version).
Normally this does not change across maintenance releases.
Please read the comment in F<patchlevel.h>.

=item C<PERL_API_VERSION>

From F<patchlevel.h>:

This number describes the earliest compatible C<PERL_VERSION> of
Perl (C<compatibility> here being defined as sufficient F<binary/C<API>>
compatibility to run C<XS> code built with the older version).
Normally this does not change across maintenance releases.
Please read the comment in F<patchlevel.h>.

=item C<PERL_CONFIG_SH>

From F<Oldsyms.U>:

This is set to C<true> in F<config.sh> so that a shell script
sourcing F<config.sh> can tell if it has been sourced already.

=item C<PERL_PATCHLEVEL>

From F<Oldsyms.U>:

This symbol reflects the patchlevel, if available. Will usually
come from the F<.patch> file, which is available when the perl
source tree was fetched with rsync.

=item C<perl_patchlevel>

From F<patchlevel.U>:

This is the Perl patch level, a numeric change identifier,
as defined by whichever source code maintenance system
is used to maintain the patches; currently Perforce.
It does not correlate with the Perl version numbers or
the maintenance versus development dichotomy except
by also being increasing.

=item C<PERL_REVISION>

From F<Oldsyms.U>:

In a Perl version number such as 5.6.2, this is the 5.
This value is manually set in F<patchlevel.h>

=item C<perl_static_inline>

From F<d_static_inline.U>:

This variable defines the C<PERL_STATIC_INLINE> symbol to
the best-guess incantation to use for static inline functions.
Possibilities include
static inline (c99)
static __inline__ (gcc -ansi)
static __inline (C<MSVC>)
static _inline (older C<MSVC>)
static (c89 compilers)

=item C<PERL_SUBVERSION>

From F<Oldsyms.U>:

In a Perl version number such as 5.6.2, this is the 2.
Values greater than 50 represent potentially unstable
development subversions.
This value is manually set in F<patchlevel.h>

=item C<PERL_VERSION>

From F<Oldsyms.U>:

In a Perl version number such as 5.6.2, this is the 6.
This value is manually set in F<patchlevel.h>

=item C<perladmin>

From F<perladmin.U>:

Electronic mail address of the perl5 administrator.

=item C<perllibs>

From F<End.U>:

The list of libraries needed by Perl only (any libraries needed
by extensions only will by dropped, if using dynamic loading).

=item C<perlpath>

From F<perlpath.U>:

This variable contains the eventual value of the C<PERLPATH> symbol,
which contains the name of the perl interpreter to be used in
shell scripts and in the "eval C<exec>" idiom. This variable is
not necessarily the pathname of the file containing the perl
interpreter; you must append the executable extension (_exe) if
it is not already present. Note that Perl code that runs during
the Perl build process cannot reference this variable, as Perl
may not have been installed, or even if installed, may be a
different version of Perl.

=item C<pg>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the pg program. After Configure runs,
the value is reset to a plain C<pg> and is not useful.

=item C<phostname>

From F<myhostname.U>:

This variable contains the eventual value of the C<PHOSTNAME> symbol,
which is a command that can be fed to popen() to get the host name.
The program should probably not presume that the domain is or isn't
there already.

=item C<pidtype>

From F<pidtype.U>:

This variable defines C<PIDTYPE> to be something like pid_t, int,
ushort, or whatever type is used to declare process ids in the kernel.

=item C<plibpth>

From F<libpth.U>:

Holds the private path used by Configure to find out the libraries.
Its value is prepend to libpth. This variable takes care of special
machines, like the mips.  Usually, it should be empty.

=item C<pmake>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<pr>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<prefix>

From F<prefix.U>:

This variable holds the name of the directory below which the
user will install the package. Usually, this is F</usr/local>, and
executables go in F</usr/local/bin>, library stuff in F</usr/local/lib>,
man pages in F</usr/local/man>, etc. It is only used to set defaults
for things in F<bin.U>, F<mansrc.U>, F<privlib.U>, or F<scriptdir.U>.

=item C<prefixexp>

From F<prefix.U>:

This variable holds the full absolute path of the directory below
which the user will install the package.  Derived from prefix.

=item C<privlib>

From F<privlib.U>:

This variable contains the eventual value of the C<PRIVLIB> symbol,
which is the name of the private library for this package. It may
have a F<~> on the front. It is up to the makefile to eventually create
this directory while performing installation (with F<~> substitution).

=item C<privlibexp>

From F<privlib.U>:

This variable is the F<~name> expanded version of privlib, so that you
may use it directly in Makefiles or shell scripts.

=item C<procselfexe>

From F<d_procselfexe.U>:

If d_procselfexe is defined, $procselfexe is the filename
of the symbolic link pointing to the absolute pathname of
the executing program.

=item C<ptrsize>

From F<ptrsize.U>:

This variable contains the value of the C<PTRSIZE> symbol, which
indicates to the C program how many bytes there are in a pointer.

=back

=head2 q

=over 4

=item C<quadkind>

From F<quadtype.U>:

This variable, if defined, encodes the type of a quad:
1 = int, 2 = long, 3 = long long, 4 = int64_t.

=item C<quadtype>

From F<quadtype.U>:

This variable defines Quad_t to be something like long, int,
long long, int64_t, or whatever type is used for 64-bit integers.

=back

=head2 r

=over 4

=item C<randbits>

From F<randfunc.U>:

Indicates how many bits are produced by the function used to
generate normalized random numbers.

=item C<randfunc>

From F<randfunc.U>:

Indicates the name of the random number function to use.
Values include drand48, random, and rand. In C programs,
the C<Drand01> macro is defined to generate uniformly distributed
random numbers over the range [0., 1.[ (see drand01 and nrand).

=item C<random_r_proto>

From F<d_random_r.U>:

This variable encodes the prototype of random_r.
It is zero if d_random_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_random_r
is defined.

=item C<randseedtype>

From F<randfunc.U>:

Indicates the type of the argument of the seedfunc.

=item C<ranlib>

From F<orderlib.U>:

This variable is set to the pathname of the ranlib program, if it is
needed to generate random libraries. Set to C<:> if ar can generate
random libraries or if random libraries are not supported

=item C<rd_nodata>

From F<nblock_io.U>:

This variable holds the return code from read() when no data is
present. It should be -1, but some systems return 0 when C<O_NDELAY> is
used, which is a shame because you cannot make the difference between
no data and an F<EOF.>. Sigh!

=item C<readdir64_r_proto>

From F<d_readdir64_r.U>:

This variable encodes the prototype of readdir64_r.
It is zero if d_readdir64_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_readdir64_r
is defined.

=item C<readdir_r_proto>

From F<d_readdir_r.U>:

This variable encodes the prototype of readdir_r.
It is zero if d_readdir_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_readdir_r
is defined.

=item C<revision>

From F<patchlevel.U>:

The value of revision comes from the F<patchlevel.h> file.
In a version number such as 5.6.1, this is the C<5>.
In F<patchlevel.h>, this is referred to as C<PERL_REVISION>.

=item C<rm>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the rm program. After Configure runs,
the value is reset to a plain C<rm> and is not useful.

=item C<rm_try>

From F<Unix.U>:

This is a cleanup variable for try test programs.
Internal Configure use only.

=item C<rmail>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<run>

From F<Cross.U>:

This variable contains the command used by Configure
to copy and execute a cross-compiled executable in the
target host.  Useful and available only during Perl build.
Empty string '' if not cross-compiling.

=item C<runnm>

From F<usenm.U>:

This variable contains C<true> or C<false> depending whether the
nm extraction should be performed or not, according to the value
of usenm and the flags on the Configure command line.

=back

=head2 s

=over 4

=item C<sched_yield>

From F<d_pthread_y.U>:

This variable defines the way to yield the execution
of the current thread.

=item C<scriptdir>

From F<scriptdir.U>:

This variable holds the name of the directory in which the user wants
to put publicly scripts for the package in question. It is either
the same directory as for binaries, or a special one that can be
mounted across different architectures, like F</usr/share>. Programs
must be prepared to deal with F<~name> expansion.

=item C<scriptdirexp>

From F<scriptdir.U>:

This variable is the same as scriptdir, but is filename expanded
at configuration time, for programs not wanting to bother with it.

=item C<sed>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the sed program. After Configure runs,
the value is reset to a plain C<sed> and is not useful.

=item C<seedfunc>

From F<randfunc.U>:

Indicates the random number generating seed function.
Values include srand48, srandom, and srand.

=item C<selectminbits>

From F<selectminbits.U>:

This variable holds the minimum number of bits operated by select.
That is, if you do select(n, ...), how many bits at least will be
cleared in the masks if some activity is detected. Usually this
is either n or 32*ceil(F<n/32>), especially many little-endians do
the latter. This is only useful if you have select(), naturally.

=item C<selecttype>

From F<selecttype.U>:

This variable holds the type used for the 2nd, 3rd, and 4th
arguments to select. Usually, this is C<fd_set *>, if C<HAS_FD_SET>
is defined, and C<int *> otherwise. This is only useful if you
have select(), naturally.

=item C<sendmail>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<setgrent_r_proto>

From F<d_setgrent_r.U>:

This variable encodes the prototype of setgrent_r.
It is zero if d_setgrent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setgrent_r
is defined.

=item C<sethostent_r_proto>

From F<d_sethostent_r.U>:

This variable encodes the prototype of sethostent_r.
It is zero if d_sethostent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_sethostent_r
is defined.

=item C<setlocale_r_proto>

From F<d_setlocale_r.U>:

This variable encodes the prototype of setlocale_r.
It is zero if d_setlocale_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setlocale_r
is defined.

=item C<setnetent_r_proto>

From F<d_setnetent_r.U>:

This variable encodes the prototype of setnetent_r.
It is zero if d_setnetent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setnetent_r
is defined.

=item C<setprotoent_r_proto>

From F<d_setprotoent_r.U>:

This variable encodes the prototype of setprotoent_r.
It is zero if d_setprotoent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setprotoent_r
is defined.

=item C<setpwent_r_proto>

From F<d_setpwent_r.U>:

This variable encodes the prototype of setpwent_r.
It is zero if d_setpwent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setpwent_r
is defined.

=item C<setservent_r_proto>

From F<d_setservent_r.U>:

This variable encodes the prototype of setservent_r.
It is zero if d_setservent_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_setservent_r
is defined.

=item C<sGMTIME_max>

From F<time_size.U>:

This variable defines the maximum value of the time_t offset that
the system function gmtime () accepts

=item C<sGMTIME_min>

From F<time_size.U>:

This variable defines the minimum value of the time_t offset that
the system function gmtime () accepts

=item C<sh>

From F<sh.U>:

This variable contains the full pathname of the shell used
on this system to execute Bourne shell scripts. Usually, this will be
F</bin/sh>, though it's possible that some systems will have F</bin/ksh>,
F</bin/pdksh>, F</bin/ash>, F</bin/bash>, or even something such as
D:F</bin/sh.exe>.
This unit comes before F<Options.U>, so you can't set sh with a C<-D>
option, though you can override this (and startsh)
with C<-O -Dsh=F</bin/whatever> -Dstartsh=whatever>

=item C<shar>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<sharpbang>

From F<spitshell.U>:

This variable contains the string #! if this system supports that
construct.

=item C<shmattype>

From F<d_shmat.U>:

This symbol contains the type of pointer returned by shmat().
It can be C<void *> or C<char *>.

=item C<shortsize>

From F<intsize.U>:

This variable contains the value of the C<SHORTSIZE> symbol which
indicates to the C program how many bytes there are in a short.

=item C<shrpenv>

From F<libperl.U>:

If the user builds a shared F<libperl.so>, then we need to tell the
C<perl> executable where it will be able to find the installed F<libperl.so>.
One way to do this on some systems is to set the environment variable
C<LD_RUN_PATH> to the directory that will be the final location of the
shared F<libperl.so>. The makefile can use this with something like
$shrpenv $(C<CC>) -o perl F<perlmain.o> $libperl $libs
Typical values are
shrpenv="env C<LD_RUN_PATH>=F<$archlibexp/C<CORE>>"
or
shrpenv=''
See the main perl F<Makefile.SH> for actual working usage.

Alternatively, we might be able to use a command line option such
as -R F<$archlibexp/C<CORE>> (Solaris) or -Wl,-rpath
F<$archlibexp/C<CORE>> (Linux).

=item C<shsharp>

From F<spitshell.U>:

This variable tells further Configure units whether your sh can
handle # comments.

=item C<sig_count>

From F<sig_name.U>:

This variable holds a number larger than the largest valid
signal number. This is usually the same as the C<NSIG> macro.

=item C<sig_name>

From F<sig_name.U>:

This variable holds the signal names, space separated. The leading
C<SIG> in signal name is removed. A C<ZERO> is prepended to the list.
This is currently not used, sig_name_init is used instead.

=item C<sig_name_init>

From F<sig_name.U>:

This variable holds the signal names, enclosed in double quotes and
separated by commas, suitable for use in the C<SIG_NAME> definition
below. A C<ZERO> is prepended to the list, and the list is
terminated with a plain 0. The leading C<SIG> in signal names
is removed. See sig_num.

=item C<sig_num>

From F<sig_name.U>:

This variable holds the signal numbers, space separated. A C<ZERO> is
prepended to the list (corresponding to the fake C<SIGZERO>).
Those numbers correspond to the value of the signal listed
in the same place within the sig_name list.
This is currently not used, sig_num_init is used instead.

=item C<sig_num_init>

From F<sig_name.U>:

This variable holds the signal numbers, enclosed in double quotes and
separated by commas, suitable for use in the C<SIG_NUM> definition
below. A C<ZERO> is prepended to the list, and the list is
terminated with a plain 0.

=item C<sig_size>

From F<sig_name.U>:

This variable contains the number of elements of the sig_name
and sig_num arrays.

=item C<signal_t>

From F<d_voidsig.U>:

This variable holds the type of the signal handler (void or int).

=item C<sitearch>

From F<sitearch.U>:

This variable contains the eventual value of the C<SITEARCH> symbol,
which is the name of the private library for this package. It may
have a F<~> on the front. It is up to the makefile to eventually create
this directory while performing installation (with F<~> substitution).
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
architecture-dependent modules in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitearchexp>

From F<sitearch.U>:

This variable is the F<~name> expanded version of sitearch, so that you
may use it directly in Makefiles or shell scripts.

=item C<sitebin>

From F<sitebin.U>:

This variable holds the name of the directory in which the user wants
to put add-on publicly executable files for the package in question. It
is most often a local directory such as F</usr/local/bin>. Programs using
this variable must be prepared to deal with F<~name> substitution.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
executables in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitebinexp>

From F<sitebin.U>:

This is the same as the sitebin variable, but is filename expanded at
configuration time, for use in your makefiles.

=item C<sitehtml1dir>

From F<sitehtml1dir.U>:

This variable contains the name of the directory in which site-specific
html source pages are to be put. It is the responsibility of the
F<Makefile.SH> to get the value of this into the proper command.
You must be prepared to do the F<~name> expansion yourself.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
html pages in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitehtml1direxp>

From F<sitehtml1dir.U>:

This variable is the same as the sitehtml1dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<sitehtml3dir>

From F<sitehtml3dir.U>:

This variable contains the name of the directory in which site-specific
library html source pages are to be put. It is the responsibility of the
F<Makefile.SH> to get the value of this into the proper command.
You must be prepared to do the F<~name> expansion yourself.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
library html pages in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitehtml3direxp>

From F<sitehtml3dir.U>:

This variable is the same as the sitehtml3dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<sitelib>

From F<sitelib.U>:

This variable contains the eventual value of the C<SITELIB> symbol,
which is the name of the private library for this package. It may
have a F<~> on the front. It is up to the makefile to eventually create
this directory while performing installation (with F<~> substitution).
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
architecture-independent modules in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitelib_stem>

From F<sitelib.U>:

This variable is $sitelibexp with any trailing version-specific component
removed. The elements in inc_version_list (F<inc_version_list.U>) can
be tacked onto this variable to generate a list of directories to search.

=item C<sitelibexp>

From F<sitelib.U>:

This variable is the F<~name> expanded version of sitelib, so that you
may use it directly in Makefiles or shell scripts.

=item C<siteman1dir>

From F<siteman1dir.U>:

This variable contains the name of the directory in which site-specific
manual source pages are to be put. It is the responsibility of the
F<Makefile.SH> to get the value of this into the proper command.
You must be prepared to do the F<~name> expansion yourself.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
man1 pages in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<siteman1direxp>

From F<siteman1dir.U>:

This variable is the same as the siteman1dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<siteman3dir>

From F<siteman3dir.U>:

This variable contains the name of the directory in which site-specific
library man source pages are to be put. It is the responsibility of the
F<Makefile.SH> to get the value of this into the proper command.
You must be prepared to do the F<~name> expansion yourself.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
man3 pages in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<siteman3direxp>

From F<siteman3dir.U>:

This variable is the same as the siteman3dir variable, but is filename
expanded at configuration time, for convenient use in makefiles.

=item C<siteprefix>

From F<siteprefix.U>:

This variable holds the full absolute path of the directory below
which the user will install add-on packages.
See C<INSTALL> for usage and examples.

=item C<siteprefixexp>

From F<siteprefix.U>:

This variable holds the full absolute path of the directory below
which the user will install add-on packages.  Derived from siteprefix.

=item C<sitescript>

From F<sitescript.U>:

This variable holds the name of the directory in which the user wants
to put add-on publicly executable files for the package in question. It
is most often a local directory such as F</usr/local/bin>. Programs using
this variable must be prepared to deal with F<~name> substitution.
The standard distribution will put nothing in this directory.
After perl has been installed, users may install their own local
scripts in this directory with
MakeMaker F<Makefile.PL>
or equivalent. See C<INSTALL> for details.

=item C<sitescriptexp>

From F<sitescript.U>:

This is the same as the sitescript variable, but is filename expanded at
configuration time, for use in your makefiles.

=item C<sizesize>

From F<sizesize.U>:

This variable contains the size of a sizetype in bytes.

=item C<sizetype>

From F<sizetype.U>:

This variable defines sizetype to be something like size_t,
unsigned long, or whatever type is used to declare length
parameters for string functions.

=item C<sleep>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<sLOCALTIME_max>

From F<time_size.U>:

This variable defines the maximum value of the time_t offset that
the system function localtime () accepts

=item C<sLOCALTIME_min>

From F<time_size.U>:

This variable defines the minimum value of the time_t offset that
the system function localtime () accepts

=item C<smail>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<so>

From F<so.U>:

This variable holds the extension used to identify shared libraries
(also known as shared objects) on the system. Usually set to C<so>.

=item C<sockethdr>

From F<d_socket.U>:

This variable has any cpp C<-I> flags needed for socket support.

=item C<socketlib>

From F<d_socket.U>:

This variable has the names of any libraries needed for socket support.

=item C<socksizetype>

From F<socksizetype.U>:

This variable holds the type used for the size argument
for various socket calls like accept.  Usual values include
socklen_t, size_t, and int.

=item C<sort>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the sort program. After Configure runs,
the value is reset to a plain C<sort> and is not useful.

=item C<spackage>

From F<package.U>:

This variable contains the name of the package being constructed,
with the first letter uppercased, F<i.e>. suitable for starting
sentences.

=item C<spitshell>

From F<spitshell.U>:

This variable contains the command necessary to spit out a runnable
shell on this system. It is either cat or a grep C<-v> for # comments.

=item C<sPRId64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit decimal numbers (format C<d>) for output.

=item C<sPRIeldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<e>) for output.

=item C<sPRIEUldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<E>) for output.
The C in the name is to separate this from sPRIeldbl so that even
case-blind systems can see the difference.

=item C<sPRIfldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<f>) for output.

=item C<sPRIFUldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<F>) for output.
The C in the name is to separate this from sPRIfldbl so that even
case-blind systems can see the difference.

=item C<sPRIgldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<g>) for output.

=item C<sPRIGUldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<G>) for output.
The C in the name is to separate this from sPRIgldbl so that even
case-blind systems can see the difference.

=item C<sPRIi64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit decimal numbers (format C) for output.

=item C<sPRIo64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit octal numbers (format C<o>) for output.

=item C<sPRIu64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit unsigned decimal numbers (format C) for output.

=item C<sPRIx64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit hexadecimal numbers (format C<x>) for output.

=item C<sPRIXU64>

From F<quadfio.U>:

This variable, if defined, contains the string used by stdio to
format 64-bit hExADECimAl numbers (format C<X>) for output.
The C in the name is to separate this from sPRIx64 so that even
case-blind systems can see the difference.

=item C<srand48_r_proto>

From F<d_srand48_r.U>:

This variable encodes the prototype of srand48_r.
It is zero if d_srand48_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_srand48_r
is defined.

=item C<srandom_r_proto>

From F<d_srandom_r.U>:

This variable encodes the prototype of srandom_r.
It is zero if d_srandom_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_srandom_r
is defined.

=item C<src>

From F<src.U>:

This variable holds the (possibly relative) path of the package source.
It is up to the Makefile to use this variable and set C<VPATH> accordingly
to find the sources remotely. Use $pkgsrc to have an absolute path.

=item C<sSCNfldbl>

From F<longdblfio.U>:

This variable, if defined, contains the string used by stdio to
format long doubles (format C<f>) for input.

=item C<ssizetype>

From F<ssizetype.U>:

This variable defines ssizetype to be something like ssize_t,
long or int.  It is used by functions that return a count
of bytes or an error condition.  It must be a signed type.
We will pick a type such that sizeof(SSize_t) == sizeof(Size_t).

=item C<st_ino_sign>

From F<st_ino_def.U>:

This variable contains the signedness of struct stat's st_ino.
1 for unsigned, -1 for signed.

=item C<st_ino_size>

From F<st_ino_def.U>:

This variable contains the size of struct stat's st_ino in bytes.

=item C<startperl>

From F<startperl.U>:

This variable contains the string to put on the front of a perl
script to make sure (hopefully) that it runs with perl and not some
shell. Of course, that leading line must be followed by the classical
perl idiom:
eval 'exec perl -S $0 ${1+C<$@>}'
if $running_under_some_shell;
to guarantee perl startup should the shell execute the script. Note
that this magic incantation is not understood by csh.

=item C<startsh>

From F<startsh.U>:

This variable contains the string to put on the front of a shell
script to make sure (hopefully) that it runs with sh and not some
other shell.

=item C<static_ext>

From F<Extensions.U>:

This variable holds a list of C<XS> extension files we want to
link statically into the package. It is used by Makefile.

=item C<stdchar>

From F<stdchar.U>:

This variable conditionally defines C<STDCHAR> to be the type of char
used in F<stdio.h>. It has the values "unsigned char" or C<char>.

=item C<stdio_base>

From F<d_stdstdio.U>:

This variable defines how, given a C<FILE> pointer, fp, to access the
_base field (or equivalent) of F<stdio.h>'s C<FILE> structure. This will
be used to define the macro FILE_base(fp).

=item C<stdio_bufsiz>

From F<d_stdstdio.U>:

This variable defines how, given a C<FILE> pointer, fp, to determine
the number of bytes store in the I/O buffer pointer to by the
_base field (or equivalent) of F<stdio.h>'s C<FILE> structure. This will
be used to define the macro FILE_bufsiz(fp).

=item C<stdio_cnt>

From F<d_stdstdio.U>:

This variable defines how, given a C<FILE> pointer, fp, to access the
_cnt field (or equivalent) of F<stdio.h>'s C<FILE> structure. This will
be used to define the macro FILE_cnt(fp).

=item C<stdio_filbuf>

From F<d_stdstdio.U>:

This variable defines how, given a C<FILE> pointer, fp, to tell
stdio to refill its internal buffers (?). This will
be used to define the macro FILE_filbuf(fp).

=item C<stdio_ptr>

From F<d_stdstdio.U>:

This variable defines how, given a C<FILE> pointer, fp, to access the
_ptr field (or equivalent) of F<stdio.h>'s C<FILE> structure. This will
be used to define the macro FILE_ptr(fp).

=item C<stdio_stream_array>

From F<stdio_streams.U>:

This variable tells the name of the array holding the stdio streams.
Usual values include _iob, __iob, and __sF.

=item C<strerror_r_proto>

From F<d_strerror_r.U>:

This variable encodes the prototype of strerror_r.
It is zero if d_strerror_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_strerror_r
is defined.

=item C<submit>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<subversion>

From F<patchlevel.U>:

The subversion level of this package.
The value of subversion comes from the F<patchlevel.h> file.
In a version number such as 5.6.1, this is the C<1>.
In F<patchlevel.h>, this is referred to as C<PERL_SUBVERSION>.
This is unique to perl.

=item C<sysman>

From F<sysman.U>:

This variable holds the place where the manual is located on this
system. It is not the place where the user wants to put his manual
pages. Rather it is the place where Configure may look to find manual
for unix commands (section 1 of the manual usually). See mansrc.

=item C<sysroot>

From F<Sysroot.U>:

This variable is empty unless supplied by the Configure user.
It can contain a path to an alternative root directory, under which
headers and libraries for the compilation target can be found. This
is generally used when cross-compiling using a gcc-like compiler.

=back

=head2 t

=over 4

=item C<tail>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<tar>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<targetarch>

From F<Cross.U>:

If cross-compiling, this variable contains the target architecture.
If not, this will be empty.

=item C<targetdir>

From F<Cross.U>:

This variable contains a path that will be created on the target
host using targetmkdir, and then used to copy the cross-compiled
executables to. Defaults to F</tmp> if not set.

=item C<targetenv>

From F<Cross.U>:

If cross-compiling, this variable can be used to modify the
environment on the target system.
However, how and where it's used, and even if it's used at all, is
entirely dependent on both the transport mechanism (targetrun) and
what the target system is.  Unless the relevant documentation says
otherwise, it is genereally not useful.

=item C<targethost>

From F<Cross.U>:

This variable contains the name of a separate host machine that
can be used to run compiled test programs and perl tests on.
Set to empty string if not in use.

=item C<targetmkdir>

From F<Cross.U>:

This variable contains the command used by Configure to create a
new directory on the target host.

=item C<targetport>

From F<Cross.U>:

This variable contains the number of a network port to be used to
connect to the host in targethost, if unset defaults to 22 for ssh.

=item C<targetsh>

From F<sh.U>:

If cross-compiling, this variable contains the location of sh on the
target system.
If not, this will be the same as $sh.

=item C<tbl>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<tee>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<test>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the test program. After Configure runs,
the value is reset to a plain C<test> and is not useful.

=item C<timeincl>

From F<i_time.U>:

This variable holds the full path of the included time header(s).

=item C<timetype>

From F<d_time.U>:

This variable holds the type returned by time(). It can be long,
or time_t on C<BSD> sites (in which case <sys/types.h> should be
included). Anyway, the type Time_t should be used.

=item C<tmpnam_r_proto>

From F<d_tmpnam_r.U>:

This variable encodes the prototype of tmpnam_r.
It is zero if d_tmpnam_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_tmpnam_r
is defined.

=item C<to>

From F<Cross.U>:

This variable contains the command used by Configure
to copy to from the target host. Useful and available
only during Perl build.
The string C<:> if not cross-compiling.

=item C<touch>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the touch program. After Configure runs,
the value is reset to a plain C<touch> and is not useful.

=item C<tr>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the tr program. After Configure runs,
the value is reset to a plain C<tr> and is not useful.

=item C<trnl>

From F<trnl.U>:

This variable contains the value to be passed to the tr(1)
command to transliterate a newline. Typical values are
C<\012> and C<\n>. This is needed for C<EBCDIC> systems where
newline is not necessarily C<\012>.

=item C<troff>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<ttyname_r_proto>

From F<d_ttyname_r.U>:

This variable encodes the prototype of ttyname_r.
It is zero if d_ttyname_r is undef, and one of the
C<REENTRANT_PROTO_T_ABC> macros of F<reentr.h> if d_ttyname_r
is defined.

=back

=head2 u

=over 4

=item C<u16size>

From F<perlxv.U>:

This variable is the size of an U16 in bytes.

=item C<u16type>

From F<perlxv.U>:

This variable contains the C type used for Perl's U16.

=item C<u32size>

From F<perlxv.U>:

This variable is the size of an U32 in bytes.

=item C<u32type>

From F<perlxv.U>:

This variable contains the C type used for Perl's U32.

=item C<u64size>

From F<perlxv.U>:

This variable is the size of an U64 in bytes.

=item C<u64type>

From F<perlxv.U>:

This variable contains the C type used for Perl's U64.

=item C<u8size>

From F<perlxv.U>:

This variable is the size of an U8 in bytes.

=item C<u8type>

From F<perlxv.U>:

This variable contains the C type used for Perl's U8.

=item C<uidformat>

From F<uidf.U>:

This variable contains the format string used for printing a Uid_t.

=item C<uidsign>

From F<uidsign.U>:

This variable contains the signedness of a uidtype.
1 for unsigned, -1 for signed.

=item C<uidsize>

From F<uidsize.U>:

This variable contains the size of a uidtype in bytes.

=item C<uidtype>

From F<uidtype.U>:

This variable defines Uid_t to be something like uid_t, int,
ushort, or whatever type is used to declare user ids in the kernel.

=item C<uname>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the uname program. After Configure runs,
the value is reset to a plain C<uname> and is not useful.

=item C<uniq>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the uniq program. After Configure runs,
the value is reset to a plain C<uniq> and is not useful.

=item C<uquadtype>

From F<quadtype.U>:

This variable defines Uquad_t to be something like unsigned long,
unsigned int, unsigned long long, uint64_t, or whatever type is
used for 64-bit integers.

=item C<use5005threads>

From F<usethreads.U>:

This variable conditionally defines the USE_5005THREADS symbol,
and indicates that Perl should be built to use the 5.005-based
threading implementation. Only valid up to 5.8.x.

=item C<use64bitall>

From F<use64bits.U>:

This variable conditionally defines the USE_64_BIT_ALL symbol,
and indicates that 64-bit integer types should be used
when available. The maximal possible
64-bitness is employed: LP64 or ILP64, meaning that you will
be able to use more than 2 gigabytes of memory. This mode is
even more binary incompatible than USE_64_BIT_INT. You may not
be able to run the resulting executable in a 32-bit C<CPU> at all or
you may need at least to reboot your C<OS> to 64-bit mode.

=item C<use64bitint>

From F<use64bits.U>:

This variable conditionally defines the USE_64_BIT_INT symbol,
and indicates that 64-bit integer types should be used
when available.  The minimal possible 64-bitness
is employed, just enough to get 64-bit integers into Perl.
This may mean using for example "long longs", while your memory
may still be limited to 2 gigabytes.

=item C<usecbacktrace>

From F<usebacktrace.U>:

This variable indicates whether we are compiling with backtrace
support.

=item C<usecrosscompile>

From F<Cross.U>:

This variable conditionally defines the C<USE_CROSS_COMPILE> symbol,
and indicates that Perl has been cross-compiled.

=item C<usedevel>

From F<Devel.U>:

This variable indicates that Perl was configured with development
features enabled.  This should not be done for production builds.

=item C<usedl>

From F<dlsrc.U>:

This variable indicates if the system supports dynamic
loading of some sort.  See also dlsrc and dlobj.

=item C<usedtrace>

From F<usedtrace.U>:

This variable indicates whether we are compiling with dtrace
support. See also dtrace.

=item C<usefaststdio>

From F<usefaststdio.U>:

This variable conditionally defines the C<USE_FAST_STDIO> symbol,
and indicates that Perl should be built to use C<fast stdio>.
Defaults to define in Perls 5.8 and earlier, to undef later.

=item C<useithreads>

From F<usethreads.U>:

This variable conditionally defines the C<USE_ITHREADS> symbol,
and indicates that Perl should be built to use the interpreter-based
threading implementation.

=item C<usekernprocpathname>

From F<usekernprocpathname.U>:

This variable, indicates that we can use sysctl with
C<KERN_PROC_PATHNAME> to get a full path for the executable, and hence
convert $^X to an absolute path.

=item C<uselanginfo>

From F<Extensions.U>:

This variable holds either C<true> or C<false> to indicate
whether the I18N::Langinfo extension should be used. The sole
use for this currently is to allow an easy mechanism for users to skip
this extension from the Configure command line.

=item C<uselargefiles>

From F<uselfs.U>:

This variable conditionally defines the C<USE_LARGE_FILES> symbol,
and indicates that large file interfaces should be used when
available.

=item C<uselongdouble>

From F<uselongdbl.U>:

This variable conditionally defines the C<USE_LONG_DOUBLE> symbol,
and indicates that long doubles should be used when available.

=item C<usemallocwrap>

From F<mallocsrc.U>:

This variable contains y if we are wrapping malloc to prevent
integer overflow during size calculations.

=item C<usemorebits>

From F<usemorebits.U>:

This variable conditionally defines the C<USE_MORE_BITS> symbol,
and indicates that explicit 64-bit interfaces and long doubles
should be used when available.

=item C<usemultiplicity>

From F<usemultiplicity.U>:

This variable conditionally defines the C<MULTIPLICITY> symbol,
and indicates that Perl should be built to use multiplicity.

=item C<usemymalloc>

From F<mallocsrc.U>:

This variable contains y if the malloc that comes with this package
is desired over the system's version of malloc. People often include
special versions of malloc for efficiency, but such versions are often
less portable. See also mallocsrc and mallocobj.
If this is C<y>, then -lmalloc is removed from $libs.

=item C<usenm>

From F<usenm.U>:

This variable contains C<true> or C<false> depending whether the
nm extraction is wanted or not.

=item C<usensgetexecutablepath>

From F<usensgetexecutablepath.U>:

This symbol, if defined, indicates that we can use _NSGetExecutablePath
and realpath to get a full path for the executable, and hence convert
$^X to an absolute path.

=item C<useopcode>

From F<Extensions.U>:

This variable holds either C<true> or C<false> to indicate
whether the Opcode extension should be used. The sole
use for this currently is to allow an easy mechanism
for users to skip the Opcode extension from the Configure
command line.

=item C<useperlio>

From F<useperlio.U>:

This variable conditionally defines the C<USE_PERLIO> symbol,
and indicates that the PerlIO abstraction should be
used throughout.

=item C<useposix>

From F<Extensions.U>:

This variable holds either C<true> or C<false> to indicate
whether the C<POSIX> extension should be used. The sole
use for this currently is to allow an easy mechanism
for hints files to indicate that C<POSIX> will not compile
on a particular system.

=item C<usequadmath>

From F<usequadmath.U>:

This variable conditionally defines the C<USE_QUADMATH> symbol,
and indicates that the quadmath library __float128 long doubles
should be used when available.

=item C<usereentrant>

From F<usethreads.U>:

This variable conditionally defines the C<USE_REENTRANT_API> symbol,
which indicates that the thread code may try to use the various
_r versions of library functions. This is only potentially
meaningful if usethreads is set and is very experimental, it is
not even prompted for.

=item C<userelocatableinc>

From F<bin.U>:

This variable is set to true to indicate that perl should relocate
@C<INC> entries at runtime based on the path to the perl binary.
Any @C<INC> paths starting F<.../> are relocated relative to the directory
containing the perl binary, and a logical cleanup of the path is then
made around the join point (removing F<dir/../> pairs)

=item C<useshrplib>

From F<libperl.U>:

This variable is set to C<true> if the user wishes
to build a shared libperl, and C<false> otherwise.

=item C<usesitecustomize>

From F<d_sitecustomize.U>:

This variable is set to true when the user requires a mechanism that
allows the sysadmin to add entries to @C<INC> at runtime. This variable
being set, makes perl run F<$sitelib/sitecustomize.pl> at startup.

=item C<usesocks>

From F<usesocks.U>:

This variable conditionally defines the C<USE_SOCKS> symbol,
and indicates that Perl should be built to use C<SOCKS>.

=item C<usethreads>

From F<usethreads.U>:

This variable conditionally defines the C<USE_THREADS> symbol,
and indicates that Perl should be built to use threads.

=item C<usevendorprefix>

From F<vendorprefix.U>:

This variable tells whether the vendorprefix
and consequently other vendor* paths are in use.

=item C<useversionedarchname>

From F<archname.U>:

This variable indicates whether to include the $api_versionstring
as a component of the $archname.

=item C<usevfork>

From F<d_vfork.U>:

This variable is set to true when the user accepts to use vfork.
It is set to false when no vfork is available or when the user
explicitly requests not to use vfork.

=item C<usrinc>

From F<usrinc.U>:

This variable holds the path of the include files, which is
usually F</usr/include>. It is mainly used by other Configure units.

=item C<uuname>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<uvoformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<UV> as an unsigned octal integer.

=item C<uvsize>

From F<perlxv.U>:

This variable is the size of a C<UV> in bytes.

=item C<uvtype>

From F<perlxv.U>:

This variable contains the C type used for Perl's C<UV>.

=item C<uvuformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<UV> as an unsigned decimal integer.

=item C<uvxformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<UV> as an unsigned hexadecimal integer in lowercase abcdef.

=item C<uvXUformat>

From F<perlxvf.U>:

This variable contains the format string used for printing
a Perl C<UV> as an unsigned hexadecimal integer in uppercase C<ABCDEF>.

=back

=head2 v

=over 4

=item C<vendorarch>

From F<vendorarch.U>:

This variable contains the value of the C<PERL_VENDORARCH> symbol.
It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
architecture-dependent modules and extensions in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorarchexp>

From F<vendorarch.U>:

This variable is the F<~name> expanded version of vendorarch, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorbin>

From F<vendorbin.U>:

This variable contains the eventual value of the C<VENDORBIN> symbol.
It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place additional
binaries in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorbinexp>

From F<vendorbin.U>:

This variable is the F<~name> expanded version of vendorbin, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorhtml1dir>

From F<vendorhtml1dir.U>:

This variable contains the name of the directory for html
pages. It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
html pages in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorhtml1direxp>

From F<vendorhtml1dir.U>:

This variable is the F<~name> expanded version of vendorhtml1dir, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorhtml3dir>

From F<vendorhtml3dir.U>:

This variable contains the name of the directory for html
library pages. It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
html pages for modules and extensions in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorhtml3direxp>

From F<vendorhtml3dir.U>:

This variable is the F<~name> expanded version of vendorhtml3dir, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorlib>

From F<vendorlib.U>:

This variable contains the eventual value of the C<VENDORLIB> symbol,
which is the name of the private library for this package.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
modules in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorlib_stem>

From F<vendorlib.U>:

This variable is $vendorlibexp with any trailing version-specific component
removed. The elements in inc_version_list (F<inc_version_list.U>) can
be tacked onto this variable to generate a list of directories to search.

=item C<vendorlibexp>

From F<vendorlib.U>:

This variable is the F<~name> expanded version of vendorlib, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorman1dir>

From F<vendorman1dir.U>:

This variable contains the name of the directory for man1
pages. It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
man1 pages in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorman1direxp>

From F<vendorman1dir.U>:

This variable is the F<~name> expanded version of vendorman1dir, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorman3dir>

From F<vendorman3dir.U>:

This variable contains the name of the directory for man3
pages. It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place their own
man3 pages in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorman3direxp>

From F<vendorman3dir.U>:

This variable is the F<~name> expanded version of vendorman3dir, so that you
may use it directly in Makefiles or shell scripts.

=item C<vendorprefix>

From F<vendorprefix.U>:

This variable holds the full absolute path of the directory below
which the vendor will install add-on packages.
See C<INSTALL> for usage and examples.

=item C<vendorprefixexp>

From F<vendorprefix.U>:

This variable holds the full absolute path of the directory below
which the vendor will install add-on packages.  Derived from vendorprefix.

=item C<vendorscript>

From F<vendorscript.U>:

This variable contains the eventual value of the C<VENDORSCRIPT> symbol.
It may have a F<~> on the front.
The standard distribution will put nothing in this directory.
Vendors who distribute perl may wish to place additional
executable scripts in this directory with
MakeMaker F<Makefile.PL> C<INSTALLDIRS>=vendor
or equivalent. See C<INSTALL> for details.

=item C<vendorscriptexp>

From F<vendorscript.U>:

This variable is the F<~name> expanded version of vendorscript, so that you
may use it directly in Makefiles or shell scripts.

=item C<version>

From F<patchlevel.U>:

The full version number of this package, such as 5.6.1 (or 5_6_1).
This combines revision, patchlevel, and subversion to get the
full version number, including any possible subversions.
This is suitable for use as a directory name, and hence is
filesystem dependent.

=item C<version_patchlevel_string>

From F<patchlevel.U>:

This is a string combining version, subversion and
perl_patchlevel (if perl_patchlevel is non-zero).
It is typically something like
'version 7 subversion 1' or
'version 7 subversion 1 patchlevel 11224'
It is computed here to avoid duplication of code in F<myconfig.SH>
and F<lib/Config.pm>.

=item C<versiononly>

From F<versiononly.U>:

If set, this symbol indicates that only the version-specific
components of a perl installation should be installed.
This may be useful for making a test installation of a new
version without disturbing the existing installation.
Setting versiononly is equivalent to setting installperl's -v option.
In particular, the non-versioned scripts and programs such as
a2p, c2ph, h2xs, pod2*, and perldoc are not installed
(see C<INSTALL> for a more complete list). Nor are the man
pages installed.
Usually, this is undef.

=item C<vi>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=back

=head2 x

=over 4

=item C<xlibpth>

From F<libpth.U>:

This variable holds extra path (space-separated) used to find
libraries on this platform, for example C<CPU>-specific libraries
(on multi-C<CPU> platforms) may be listed here.

=back

=head2 y

=over 4

=item C<yacc>

From F<yacc.U>:

This variable holds the name of the compiler compiler we
want to use in the Makefile. It can be yacc, byacc, or bison -y.

=item C<yaccflags>

From F<yacc.U>:

This variable contains any additional yacc flags desired by the
user.  It is up to the Makefile to use this.

=back

=head2 z

=over 4

=item C<zcat>

From F<Loc.U>:

This variable is defined but not used by Configure.
The value is the empty string and is not useful.

=item C<zip>

From F<Loc.U>:

This variable is used internally by Configure to determine the
full pathname (if any) of the zip program. After Configure runs,
the value is reset to a plain C<zip> and is not useful.

=back

=head1 GIT DATA

Information on the git commit from which the current perl binary was compiled
can be found in the variable C<$Config::Git_Data>. The variable is a
structured string that looks something like this:

git_commit_id='ea0c2dbd5f5ac6845ecc7ec6696415bf8e27bd52'
  git_describe='GitLive-blead-1076-gea0c2db'
  git_branch='smartmatch'
  git_uncommitted_changes=''
  git_commit_id_title='Commit id:'
  git_commit_date='2009-05-09 17:47:31 +0200'

Its format is not guaranteed not to change over time.

=head1 NOTE

This module contains a good example of how to use tie to implement a
cache and an example of how to make a tied variable readonly to those
outside of it.

=cut

BATAL