mg.c: Remove poorly considered assertion

[perl5.git] / Porting / Glossary

!!!!!!!   DO NOT EDIT THIS FILE   !!!!!!!
This file is built by metaconfig.

This file contains a description of all the shell variables whose value is
determined by the Configure script.  Variables intended for use in C
programs (e.g. I_UNISTD) are already described in config_h.SH.  [`configpm'
generates pod documentation for Config.pm from this file--please try to keep
the formatting regular.]

_a (Unix.U):
        This variable defines the extension used for ordinary library files.
        For unix, it is '.a'.  The '.' is included.  Other possible
        values include '.lib'.

_exe (Unix.U):
        This variable defines the extension used for executable files.
        DJGPP, Cygwin and OS/2 use '.exe'.  Stratus VOS uses '.pm'.
        On operating systems which do not require a specific extension
        for executable files, this variable is empty.

_o (Unix.U):
        This variable defines the extension used for object files.
        For unix, it is '.o'.  The '.' is included.  Other possible
        values include '.obj'.

afs (afs.U):
        This variable is set to 'true' if AFS (Andrew File System) is used
        on the system, '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.

afsroot (afs.U):
        This variable is by default set to '/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.

alignbytes (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.

ansi2knr (ansi2knr.U):
        This variable is set if the user needs to run ansi2knr.
        Currently, this is not supported, so we just abort.

aphostname (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.

api_revision (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 '5.6.1', api_revision is the '5'.
        Prior to 5.5.640, the format was a floating point number,
        like 5.00563.

        perl.c:incpush() and lib/lib.pm will automatically search in
        $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 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 inc_version_list.U.

        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 patchlevel.h.
        Perhaps what we ought to do is take the hard-wired value from
        patchlevel.h but then modify it if the current Configure
        options warrant.  patchlevel.h then would use an #ifdef guard.

api_subversion (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 '5.6.1', api_subversion is the '1'.  See api_revision for
        full details.

api_version (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 '5.6.1', api_version is the '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.)

api_versionstring (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.

ar (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 "ar" and is not useful.

archlib (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 /usr/local/lib.
        Programs using this variable must be prepared to deal
        with filename expansion.

archlibexp (archlib.U):
        This variable is the same as the archlib variable, but is
        filename expanded at configuration time, for convenient use.

archname (archname.U):
        This variable is a short name to characterize the current
        architecture.  It is used mainly to construct the default archlib.

archname64 (use64bits.U):
        This variable is used for the 64-bitness part of $archname.

archobjs (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 OS/2, for example, this would
        include os2/os2.obj.

asctime_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_asctime_r
        is defined.

awk (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 "awk" and is not useful.

baserev (baserev.U):
        The base revision level of this package, from the .package file.

bash (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

bin (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 /usr/local/bin. Programs using
        this variable must be prepared to deal with ~name substitution.

bin_ELF (dlsrc.U):
        This variable saves the result from configure if generated binaries
        are in ELF format. Only set to defined when the test has actually
        been performed, and the result was positive.

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

bison (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 "bison" and is not useful.

byacc (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 "byacc" and is not useful.

byteorder (byteorder.U):
        This variable holds the byte order in a 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 !

c (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".

castflags (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

cat (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 "cat" and is not useful.

cc (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 'cc' and 'gcc'.
        Fervent ANSI compilers may be called 'c89'.  AIX has xlc.

cccdlflags (dlsrc.U):
        This variable contains any special flags that might need to be
        passed with '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.

ccdlflags (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.

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

ccflags_uselargefiles (uselfs.U):
        This variable contains the compiler flags needed by large file builds
        and added to ccflags by hints files.

ccname (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 'workshop'.

ccsymbols (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.

ccversion (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.

cf_by (cf_who.U):
        Login name of the person who ran the Configure script and answered the
        questions. This is used to tag both config.sh and config_h.SH.

cf_email (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 MailList.U.

cf_time (cf_who.U):
        Holds the output of the "date" command when the configuration file was
        produced. This is used to tag both config.sh and config_h.SH.

charbits (charsize.U):
        This variable contains the value of the CHARBITS symbol, which
        indicates to the C program how many bits there are in a character.

charsize (charsize.U):
        This variable contains the value of the CHARSIZE symbol, which
        indicates to the C program how many bytes there are in a character.

chgrp (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

chmod (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 "chmod" and is not useful.

chown (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

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

comm (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 "comm" and is not useful.

compress (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

config_arg0 (Options.U):
        This variable contains the string used to invoke the Configure
        command, as reported by the shell in the $0 variable.

config_argc (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.

config_args (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]*.

contains (contains.U):
        This variable holds the command to do a grep with a proper return
        status.  On most sane systems it is simply "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.

cp (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 "cp" and is not useful.

cpio (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

cpp (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 "cpp" and is not useful.

cpp_stuff (cpp_stuff.U):
        This variable contains an identification of the concatenation mechanism
        used by the C preprocessor.

cppccsymbols (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.

cppflags (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.

cpplast (cppstdin.U):
        This variable has the same functionality as cppminus, only it applies
        to cpprun and not cppstdin.

cppminus (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 "-" if cppstdin needs
        a minus to specify standard input, otherwise the value is "".

cpprun (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.

cppstdin (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.

cppsymbols (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.

crypt_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_crypt_r
        is defined.

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

csh (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 "csh" and is not useful.

ctermid_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_ctermid_r
        is defined.

ctime_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_ctime_r
        is defined.

d__fwalk (d__fwalk.U):
        This variable conditionally defines HAS__FWALK if _fwalk() is
        available to apply a function to all the file handles.

d_access (d_access.U):
        This variable conditionally defines HAS_ACCESS if the access() system
        call is available to check for access permissions using real IDs.

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

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

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

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

d_archlib (archlib.U):
        This variable conditionally defines 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.

d_asctime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_ASCTIME64 symbol, which
        indicates to the C program that the asctime64 () routine is available.

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

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

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

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

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

d_attribute_deprecated (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_DEPRECATED, which
        indicates that GCC can handle the attribute for marking deprecated
        APIs

d_attribute_format (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_FORMAT, which
        indicates the C compiler can check for printf-like formats.

d_attribute_malloc (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_MALLOC, which
        indicates the C compiler can understand functions as having
        malloc-like semantics.

d_attribute_nonnull (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_NONNULL, which
        indicates that the C compiler can know that certain arguments
        must not be NULL, and will check accordingly at compile time.

d_attribute_noreturn (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_NORETURN, which
        indicates that the C compiler can know that certain functions
        are guaranteed never to return.

d_attribute_pure (d_attribut.U):
        This variable conditionally defines HASATTRIBUTE_PURE, which
        indicates that the C compiler can know that certain functions
        are "pure" functions, meaning that they have no side effects, and
        only rely on function input and/or global data for their results.

d_attribute_unused (d_attribut.U):
        This variable conditionally defines 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.

d_attribute_warn_unused_result (d_attribut.U):
        This variable conditionally defines
        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().

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

d_bcmp (d_bcmp.U):
        This variable conditionally defines the HAS_BCMP symbol if
        the bcmp() routine is available to compare strings.

d_bcopy (d_bcopy.U):
        This variable conditionally defines the HAS_BCOPY symbol if
        the bcopy() routine is available to copy strings.

d_bsd (Guess.U):
        This symbol conditionally defines the symbol BSD when running on a
        BSD system.

d_bsdgetpgrp (d_getpgrp.U):
        This variable conditionally defines USE_BSD_GETPGRP if
        getpgrp needs one arguments whereas USG one needs none.

d_bsdsetpgrp (d_setpgrp.U):
        This variable conditionally defines USE_BSD_SETPGRP if
        setpgrp needs two arguments whereas USG one needs none.
        See also d_setpgid for a POSIX interface.

d_builtin_choose_expr (d_builtin.U):
        This conditionally defines HAS_BUILTIN_CHOOSE_EXPR, which
        indicates that the compiler supports __builtin_choose_expr(x,y,z).
        This built-in function is analogous to the "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.

d_builtin_expect (d_builtin.U):
        This conditionally defines 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.

d_bzero (d_bzero.U):
        This variable conditionally defines the HAS_BZERO symbol if
        the bzero() routine is available to set memory to 0.

d_c99_variadic_macros (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.

d_casti32 (d_casti32.U):
        This variable conditionally defines CASTI32, which indicates
        whether the C compiler can cast large floats to 32-bit ints.

d_castneg (d_castneg.U):
        This variable conditionally defines CASTNEG, which indicates
        whether the C compiler can cast negative float to unsigned.

d_cbrt (d_cbrt.U):
        This variable conditionally defines the HAS_CBRT symbol, which
        indicates to the C program that the cbrt() routine is available.

d_charvspr (d_vprintf.U):
        This variable conditionally defines CHARVSPRINTF if this system
        has vsprintf returning type (char*).  The trend seems to be to
        declare it as "int vsprintf()".

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

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

d_chsize (d_chsize.U):
        This variable conditionally defines the 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.

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

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

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

d_closedir (d_closedir.U):
        This variable conditionally defines HAS_CLOSEDIR if closedir() is
        available.

d_cmsghdr_s (d_cmsghdr_s.U):
        This variable conditionally defines the HAS_STRUCT_CMSGHDR symbol,
        which indicates that the struct cmsghdr is supported.

d_const (d_const.U):
        This variable conditionally defines the HASCONST symbol, which
        indicates to the C program that this C compiler knows about the
        const type.

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

d_cplusplus (d_cplusplus.U):
        This variable conditionally defines the USE_CPLUSPLUS symbol, which
        indicates that a C++ compiler was used to compiled Perl and will be
        used to compile extensions.

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

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

d_csh (d_csh.U):
        This variable conditionally defines the CSH symbol, which
        indicates to the C program that the C-shell exists.

d_ctermid (d_ctermid.U):
        This variable conditionally defines CTERMID if ctermid() is
        available to generate filename for terminal.

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

d_ctime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_CTIME64 symbol, which
        indicates to the C program that the ctime64 () routine is available.

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

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

d_dbl_dig (d_dbl_dig.U):
        This variable conditionally defines d_dbl_dig if this system's
        header files provide DBL_DIG, which is the number of significant
        digits in a double precision number.

d_dbminitproto (d_dbminitproto.U):
        This variable conditionally defines the 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.

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

d_difftime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_DIFFTIME64 symbol, which
        indicates to the C program that the difftime64 () routine is available.

d_dir_dd_fd (d_dir_dd_fd.U):
        This variable conditionally defines the HAS_DIR_DD_FD symbol, which
        indicates that the DIR directory stream type contains a member
        variable called dd_fd.

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

d_dirnamlen (i_dirent.U):
        This variable conditionally defines DIRNAMLEN, which indicates
        to the C program that the length of directory entry names is
        provided by a d_namelen field.

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

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

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

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

d_dosuid (d_dosuid.U):
        This variable conditionally defines the symbol DOSUID, which
        tells the C program that it should insert setuid emulation code
        on hosts which have setuid #! scripts disabled.

d_drand48_r (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.

d_drand48proto (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.

d_dup2 (d_dup2.U):
        This variable conditionally defines HAS_DUP2 if dup2() is
        available to duplicate file descriptors.

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

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

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

d_endhent (d_endhent.U):
        This variable conditionally defines HAS_ENDHOSTENT if endhostent() is
        available to close whatever was being used for host queries.

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

d_endnent (d_endnent.U):
        This variable conditionally defines HAS_ENDNETENT if endnetent() is
        available to close whatever was being used for network queries.

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

d_endpent (d_endpent.U):
        This variable conditionally defines HAS_ENDPROTOENT if endprotoent() is
        available to close whatever was being used for protocol queries.

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

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

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

d_endsent (d_endsent.U):
        This variable conditionally defines HAS_ENDSERVENT if endservent() is
        available to close whatever was being used for service queries.

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

d_eofnblk (nblock_io.U):
        This variable conditionally defines EOF_NONBLOCK if EOF can be seen
        when reading from a non-blocking I/O source.

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

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

d_eunice (Guess.U):
        This variable conditionally defines the symbols EUNICE and VAX, which
        alerts the C program that it must deal with idiosyncrasies of VMS.

d_exp2 (d_exp2.U):
        This variable conditionally defines the HAS_EXP2 symbol, which
        indicates to the C program that the exp2() routine is available.

d_expm1 (d_expm1.U):
        This variable conditionally defines the HAS_EXPM1 symbol, which
        indicates to the C program that the expm1() routine is available.

d_faststdio (d_faststdio.U):
        This variable conditionally defines the HAS_FAST_STDIO symbol,
        which indicates to the C program that the "fast stdio" is available
        to manipulate the stdio buffers directly.

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

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

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

d_fcntl (d_fcntl.U):
        This variable conditionally defines the HAS_FCNTL symbol, and indicates
        whether the fcntl() function exists

d_fcntl_can_lock (d_fcntl_can_lock.U):
        This variable conditionally defines the FCNTL_CAN_LOCK symbol
        and indicates whether file locking with fcntl() works.

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

d_fd_macros (d_fd_set.U):
        This variable contains the eventual value of the HAS_FD_MACROS symbol,
        which indicates if your C compiler knows about the macros which
        manipulate an fd_set.

d_fd_set (d_fd_set.U):
        This variable contains the eventual value of the HAS_FD_SET symbol,
        which indicates if your C compiler knows about the fd_set typedef.

d_fds_bits (d_fd_set.U):
        This variable contains the eventual value of the 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, HAS_FDS_BITS will let us know how to fix the gaffe.

d_fegetround (d_fegetround.U):
        This variable conditionally defines HAS_FEGETROUND if fegetround() is
        available to get the floating point rounding mode.

d_fgetpos (d_fgetpos.U):
        This variable conditionally defines HAS_FGETPOS if fgetpos() is
        available to get the file position indicator.

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

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

d_flexfnam (d_flexfnam.U):
        This variable conditionally defines the FLEXFILENAMES symbol, which
        indicates that the system supports filenames longer than 14 characters.

d_flock (d_flock.U):
        This variable conditionally defines HAS_FLOCK if flock() is
        available to do file locking.

d_flockproto (d_flockproto.U):
        This variable conditionally defines the 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.

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

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

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

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

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

d_fp_classify (d_fpclassify.U):
        This variable conditionally defines the HAS_FP_CLASSIFY symbol, which
        indicates to the C program that the fp_classify() routine is available.

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

d_fpathconf (d_pathconf.U):
        This variable conditionally defines the 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.

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

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

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

d_fpgetround (d_fpgetround.U):
        This variable conditionally defines HAS_FPGETROUND if fpgetround()
        is available to get the floating point rounding mode.

d_fpos64_t (d_fpos64_t.U):
        This symbol will be defined if the C compiler supports fpos64_t.

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

d_fs_data_s (d_fs_data_s.U):
        This variable conditionally defines the HAS_STRUCT_FS_DATA symbol,
        which indicates that the struct fs_data is supported.

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

d_fsetpos (d_fsetpos.U):
        This variable conditionally defines HAS_FSETPOS if fsetpos() is
        available to set the file position indicator.

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

d_fstatvfs (d_statvfs.U):
        This variable conditionally defines the HAS_FSTATVFS symbol, which
        indicates to the C program that the fstatvfs() routine is available.

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

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

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

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

d_Gconvert (d_gconvert.U):
        This variable holds what Gconvert is defined as to convert
        floating point numbers into strings.  By default, Configure
        sets 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 uselongdouble.cbu
        call-back unit so that long doubles can be formatted without
        loss of precision.

d_gdbm_ndbm_h_uses_prototypes (i_ndbm.U):
        This variable conditionally defines the NDBM_H_USES_PROTOTYPES symbol,
        which indicates that the gdbm-ndbm.h include file uses real 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 ndbm.h include files.

d_gdbmndbm_h_uses_prototypes (i_ndbm.U):
        This variable conditionally defines the NDBM_H_USES_PROTOTYPES symbol,
        which indicates that the gdbm/ndbm.h include file uses real 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 ndbm.h include files.

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

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

d_getespwnam (d_getespwnam.U):
        This variable conditionally defines HAS_GETESPWNAM if getespwnam() is
        available to retrieve enhanced (shadow) password entries by name.

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

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

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

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

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

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

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

d_gethbyname (d_gethbynm.U):
        This variable conditionally defines the 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.

d_gethent (d_gethent.U):
        This variable conditionally defines HAS_GETHOSTENT if gethostent() is
        available to look up host names in some data base or another.

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

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

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

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

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

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

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

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

d_getmnt (d_getmnt.U):
        This variable conditionally defines the 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.

d_getmntent (d_getmntent.U):
        This variable conditionally defines the 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.

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

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

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

d_getnent (d_getnent.U):
        This variable conditionally defines HAS_GETNETENT if getnetent() is
        available to look up network names in some data base or another.

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

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

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

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

d_getpagsz (d_getpagsz.U):
        This variable conditionally defines HAS_GETPAGESIZE if getpagesize()
        is available to get the system page size.

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

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

d_getpent (d_getpent.U):
        This variable conditionally defines HAS_GETPROTOENT if getprotoent() is
        available to look up protocols in some data base or another.

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

d_getpgrp (d_getpgrp.U):
        This variable conditionally defines HAS_GETPGRP if getpgrp() is
        available to get the current process group.

d_getpgrp2 (d_getpgrp2.U):
        This variable conditionally defines the HAS_GETPGRP2 symbol, which
        indicates to the C program that the getpgrp2() (as in DG/UX) routine
        is available to get the current process group.

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

d_getprior (d_getprior.U):
        This variable conditionally defines HAS_GETPRIORITY if getpriority()
        is available to get a process's priority.

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

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

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

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

d_getprpwnam (d_getprpwnam.U):
        This variable conditionally defines HAS_GETPRPWNAM if getprpwnam() is
        available to retrieve protected (shadow) password entries by name.

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

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

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

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

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

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

d_getsent (d_getsent.U):
        This variable conditionally defines HAS_GETSERVENT if getservent() is
        available to look up network services in some data base or another.

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

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

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

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

d_getspnam (d_getspnam.U):
        This variable conditionally defines HAS_GETSPNAM if getspnam() is
        available to retrieve SysV shadow password entries by name.

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

d_gettimeod (d_ftime.U):
        This variable conditionally defines the 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>.

d_gmtime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_GMTIME64 symbol, which
        indicates to the C program that the gmtime64 () routine is available.

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

d_gnulibc (d_gnulibc.U):
        Defined if we're dealing with the GNU C Library.

d_grpasswd (i_grp.U):
        This variable conditionally defines GRPASSWD, which indicates
        that struct group in <grp.h> contains gr_passwd.

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

d_htonl (d_htonl.U):
        This variable conditionally defines HAS_HTONL if htonl() and its
        friends are available to do network order byte swapping.

d_hypot (d_hypot.U):
        This variable conditionally defines HAS_HYPOT if hypot is available
        for numerically stable hypotenuse function.

d_ilogb (d_ilogb.U):
        This variable conditionally defines the 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.

d_ilogbl (d_ilogbl.U):
        This variable conditionally defines the 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.

d_inc_version_list (inc_version_list.U):
        This variable conditionally defines PERL_INC_VERSION_LIST.
        It is set to undef when PERL_INC_VERSION_LIST is empty.

d_index (d_strchr.U):
        This variable conditionally defines HAS_INDEX if index() and
        rindex() are available for string searching.

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

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

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

d_int64_t (d_int64_t.U):
        This symbol will be defined if the C compiler supports int64_t.

d_ip_mreq (d_socket.U):
        This variable conditionally defines the HAS_IP_MREQ symbol, which
        indicates the availability of a struct ip_mreq.

d_ip_mreq_source (d_socket.U):
        This variable conditionally defines the HAS_IP_MREQ_SOURCE symbol,
        which indicates the availability of a struct ip_mreq_source.

d_ipv6_mreq (d_socket.U):
        This variable conditionally defines the HAS_IPV6_MREQ symbol, which
        indicates the availability of a struct ipv6_mreq.

d_ipv6_mreq_source (d_socket.U):
        This variable conditionally defines the HAS_IPV6_MREQ_SOURCE symbol,
        which indicates the availability of a struct ipv6_mreq_source.

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

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

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

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

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

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

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

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

d_j0 (d_j0.U):
        This variable conditionally defines the HAS_J0 symbol, which
        indicates to the C program that the j0() routine is available.

d_j0l (d_j0.U):
        This variable conditionally defines the HAS_J0L symbol, which
        indicates to the C program that the j0l() routine is available.

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

d_lc_monetary_2008 (d_lc_monetary_2008.U):
        This variable conditionally defines HAS_LC_MONETARY_2008 if libc
        has the international currency locale rules from POSIX
        1003.1-2008.

d_lchown (d_lchown.U):
        This variable conditionally defines the 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).

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

d_ldexpl (d_longdbl.U):
        This variable conditionally defines the HAS_LDEXPL symbol, which
        indicates to the C program that the ldexpl() routine is available.

d_lgamma (d_lgamma.U):
        This variable conditionally defines the 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.

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

d_libm_lib_version (d_libm_lib_version.U):
        This variable conditionally defines the LIBM_LIB_VERSION symbol,
        which indicates to the C program that math.h defines _LIB_VERSION
        being available in libm

d_libname_unique (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 'undef'.

d_link (d_link.U):
        This variable conditionally defines HAS_LINK if link() is
        available to create hard links.

d_llrint (d_llrint.U):
        This variable conditionally defines the HAS_LLRINT symbol, which
        indicates to the C program that the llrint() routine is available
        to return the long long value closest to (according to the current
        rounding mode) to x.

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

d_localtime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_LOCALTIME64 symbol, which
        indicates to the C program that the localtime64 () routine is available.

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

d_localtime_r_needs_tzset (d_localtime_r.U):
        This variable conditionally defines the LOCALTIME_R_NEEDS_TZSET
        symbol, which makes us call tzset before localtime_r()

d_locconv (d_locconv.U):
        This variable conditionally defines HAS_LOCALECONV if localeconv() is
        available for numeric and monetary formatting conventions.

d_lockf (d_lockf.U):
        This variable conditionally defines HAS_LOCKF if lockf() is
        available to do file locking.

d_log1p (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.

d_log2 (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.

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

d_longdbl (d_longdbl.U):
        This variable conditionally defines HAS_LONG_DOUBLE if
        the long double type is supported.

d_longlong (d_longlong.U):
        This variable conditionally defines HAS_LONG_LONG if
        the long long type is supported.

d_lrint (d_lrint.U):
        This variable conditionally defines the HAS_LRINT symbol, which
        indicates to the C program that the lrint() routine is available
        to return the integral value closest to (according to the current
        rounding mode) to x.

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

d_lseekproto (d_lseekproto.U):
        This variable conditionally defines the 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.

d_lstat (d_lstat.U):
        This variable conditionally defines HAS_LSTAT if lstat() is
        available to do file stats on symbolic links.

d_madvise (d_madvise.U):
        This variable conditionally defines HAS_MADVISE if madvise() is
        available to map a file into memory.

d_malloc_good_size (d_malloc_size.U):
        This symbol, if defined, indicates that the malloc_good_size
        routine is available for use.

d_malloc_size (d_malloc_size.U):
        This symbol, if defined, indicates that the malloc_size
        routine is available for use.

d_mblen (d_mblen.U):
        This variable conditionally defines the 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.

d_mbstowcs (d_mbstowcs.U):
        This variable conditionally defines the 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.

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

d_memchr (d_memchr.U):
        This variable conditionally defines the HAS_MEMCHR symbol, which
        indicates to the C program that the memchr() routine is available
        to locate characters within a C string.

d_memcmp (d_memcmp.U):
        This variable conditionally defines the HAS_MEMCMP symbol, which
        indicates to the C program that the memcmp() routine is available
        to compare blocks of memory.

d_memcpy (d_memcpy.U):
        This variable conditionally defines the HAS_MEMCPY symbol, which
        indicates to the C program that the memcpy() routine is available
        to copy blocks of memory.

d_memmove (d_memmove.U):
        This variable conditionally defines the HAS_MEMMOVE symbol, which
        indicates to the C program that the memmove() routine is available
        to copy potentially overlapping blocks of memory.

d_memset (d_memset.U):
        This variable conditionally defines the HAS_MEMSET symbol, which
        indicates to the C program that the memset() routine is available
        to set blocks of memory.

d_mkdir (d_mkdir.U):
        This variable conditionally defines the HAS_MKDIR symbol, which
        indicates to the C program that the mkdir() routine is available
        to create directories..

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

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

d_mkstemp (d_mkstemp.U):
        This variable conditionally defines the 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.

d_mkstemps (d_mkstemps.U):
        This variable conditionally defines the 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.

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

d_mktime64 (d_timefuncs64.U):
        This variable conditionally defines the HAS_MKTIME64 symbol, which
        indicates to the C program that the mktime64 () routine is available.

d_mmap (d_mmap.U):
        This variable conditionally defines HAS_MMAP if mmap() is
        available to map a file into memory.

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

d_modfl_pow32_bug (d_modfl.U):
        This variable conditionally defines the HAS_MODFL_POW32_BUG symbol,
        which indicates that modfl() is broken for long doubles >= pow(2, 32).
        For example from 4294967303.150000 one would get 4294967302.000000
        and 1.150000.  The bug has been seen in certain versions of glibc,
        release 2.2.2 is known to be okay.

d_modflproto (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 *);

d_mprotect (d_mprotect.U):
        This variable conditionally defines HAS_MPROTECT if mprotect() is
        available to modify the access protection of a memory mapped file.

d_msg (d_msg.U):
        This variable conditionally defines the HAS_MSG symbol, which
        indicates that the entire msg*(2) library is present.

d_msg_ctrunc (d_socket.U):
        This variable conditionally defines the HAS_MSG_CTRUNC symbol,
        which indicates that the MSG_CTRUNC is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

d_msg_dontroute (d_socket.U):
        This variable conditionally defines the HAS_MSG_DONTROUTE symbol,
        which indicates that the MSG_DONTROUTE is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

d_msg_oob (d_socket.U):
        This variable conditionally defines the HAS_MSG_OOB symbol,
        which indicates that the MSG_OOB is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

d_msg_peek (d_socket.U):
        This variable conditionally defines the HAS_MSG_PEEK symbol,
        which indicates that the MSG_PEEK is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

d_msg_proxy (d_socket.U):
        This variable conditionally defines the HAS_MSG_PROXY symbol,
        which indicates that the MSG_PROXY is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

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

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

d_msghdr_s (d_msghdr_s.U):
        This variable conditionally defines the HAS_STRUCT_MSGHDR symbol,
        which indicates that the struct msghdr is supported.

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

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

d_msync (d_msync.U):
        This variable conditionally defines HAS_MSYNC if msync() is
        available to synchronize a mapped file.

d_munmap (d_munmap.U):
        This variable conditionally defines HAS_MUNMAP if munmap() is
        available to unmap a region mapped by mmap().

d_mymalloc (mallocsrc.U):
        This variable conditionally defines MYMALLOC in case other parts
        of the source want to take special action if MYMALLOC is used.
        This may include different sorts of profiling or error detection.

d_nan (d_nan.U):
        This variable conditionally defines HAS_NAN if nan() is
        available to generate NaN.

d_ndbm (i_ndbm.U):
        This variable conditionally defines the HAS_NDBM symbol, which
        indicates that both the 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.

d_ndbm_h_uses_prototypes (i_ndbm.U):
        This variable conditionally defines the NDBM_H_USES_PROTOTYPES symbol,
        which indicates that the ndbm.h include file uses real 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 ndbm.h include files.

d_nearbyint (d_nearbyint.U):
        This variable conditionally defines HAS_NEARBYINT if nearbyint()
        is available to return the integral value closest to (according to
        the current rounding mode) to x.

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

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

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

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

d_nv_preserves_uv (perlxv.U):
        This variable indicates whether a variable of type nvtype
        can preserve all the bits a variable of type uvtype.

d_nv_zero_is_allbits_zero (perlxv.U):
        This variable indicates whether a variable of type nvtype
        stores 0.0 in memory as all bits zero.

d_off64_t (d_off64_t.U):
        This symbol will be defined if the C compiler supports off64_t.

d_old_pthread_create_joinable (d_pthrattrj.U):
        This variable conditionally defines pthread_create_joinable.
        undef if pthread.h defines PTHREAD_CREATE_JOINABLE.

d_oldpthreads (usethreads.U):
        This variable conditionally defines the OLD_PTHREADS_API symbol,
        and indicates that Perl should be built to use the old
        draft POSIX threads API.  This is only potentially meaningful if
        usethreads is set.

d_oldsock (d_socket.U):
        This variable conditionally defines the OLDSOCKET symbol, which
        indicates that the BSD socket interface is based on 4.1c and not 4.2.

d_open3 (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.

d_pathconf (d_pathconf.U):
        This variable conditionally defines the 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.

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

d_perl_otherlibdirs (otherlibdirs.U):
        This variable conditionally defines PERL_OTHERLIBDIRS, which
        contains a colon-separated set of paths for the perl binary to
        include in @INC.  See also otherlibdirs.

d_phostname (d_gethname.U):
        This variable conditionally defines the HAS_PHOSTNAME symbol, which
        contains the shell command which, when fed to popen(), may be
        used to derive the host name.

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

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

d_portable (d_portable.U):
        This variable conditionally defines the PORTABLE symbol, which
        indicates to the C program that it should not assume that it is
        running on the machine it was compiled on.

d_prctl (d_prctl.U):
        This variable conditionally defines the 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.

d_prctl_set_name (d_prctl.U):
        This variable conditionally defines the HAS_PRCTL_SET_NAME symbol,
        which indicates to the C program that the prctl() routine supports
        the PR_SET_NAME option.

d_PRId64 (quadfio.U):
        This variable conditionally defines the PERL_PRId64 symbol, which
        indicates that stdio has a symbol to print 64-bit decimal numbers.

d_PRIeldbl (longdblfio.U):
        This variable conditionally defines the PERL_PRIfldbl symbol, which
        indicates that stdio has a symbol to print long doubles.

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

d_PRIfldbl (longdblfio.U):
        This variable conditionally defines the PERL_PRIfldbl symbol, which
        indicates that stdio has a symbol to print long doubles.

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

d_PRIgldbl (longdblfio.U):
        This variable conditionally defines the PERL_PRIfldbl symbol, which
        indicates that stdio has a symbol to print long doubles.

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

d_PRIi64 (quadfio.U):
        This variable conditionally defines the PERL_PRIi64 symbol, which
        indicates that stdio has a symbol to print 64-bit decimal numbers.

d_printf_format_null (d_attribut.U):
        This variable conditionally defines PRINTF_FORMAT_NULL_OK, which
        indicates the C compiler allows printf-like formats to be null.

d_PRIo64 (quadfio.U):
        This variable conditionally defines the PERL_PRIo64 symbol, which
        indicates that stdio has a symbol to print 64-bit octal numbers.

d_PRIu64 (quadfio.U):
        This variable conditionally defines the PERL_PRIu64 symbol, which
        indicates that stdio has a symbol to print 64-bit unsigned decimal
        numbers.

d_PRIx64 (quadfio.U):
        This variable conditionally defines the PERL_PRIx64 symbol, which
        indicates that stdio has a symbol to print 64-bit hexadecimal numbers.

d_PRIXU64 (quadfio.U):
        This variable conditionally defines the PERL_PRIXU64 symbol, which
        indicates that stdio has a symbol to print 64-bit hExADECimAl numbers.
        The 'U' in the name is to separate this from d_PRIx64 so that even
        case-blind systems can see the difference.

d_procselfexe (d_procselfexe.U):
        Defined if $procselfexe is symlink to the absolute
        pathname of the executing program.

d_pseudofork (d_vfork.U):
        This variable conditionally defines the HAS_PSEUDOFORK symbol,
        which indicates that an emulation of the fork routine is available.

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

d_pthread_attr_setscope (d_pthread_attr_ss.U):
        This variable conditionally defines HAS_PTHREAD_ATTR_SETSCOPE if
        pthread_attr_setscope() is available to set the contention scope
        attribute of a thread attribute object.

d_pthread_yield (d_pthread_y.U):
        This variable conditionally defines the HAS_PTHREAD_YIELD
        symbol if the pthread_yield routine is available to yield
        the execution of the current thread.

d_ptrdiff_t (d_ptrdiff_t.U):
        This symbol will be defined if the C compiler supports ptrdiff_t.

d_pwage (i_pwd.U):
        This variable conditionally defines PWAGE, which indicates
        that struct passwd contains pw_age.

d_pwchange (i_pwd.U):
        This variable conditionally defines PWCHANGE, which indicates
        that struct passwd contains pw_change.

d_pwclass (i_pwd.U):
        This variable conditionally defines PWCLASS, which indicates
        that struct passwd contains pw_class.

d_pwcomment (i_pwd.U):
        This variable conditionally defines PWCOMMENT, which indicates
        that struct passwd contains pw_comment.

d_pwexpire (i_pwd.U):
        This variable conditionally defines PWEXPIRE, which indicates
        that struct passwd contains pw_expire.

d_pwgecos (i_pwd.U):
        This variable conditionally defines PWGECOS, which indicates
        that struct passwd contains pw_gecos.

d_pwpasswd (i_pwd.U):
        This variable conditionally defines PWPASSWD, which indicates
        that struct passwd contains pw_passwd.

d_pwquota (i_pwd.U):
        This variable conditionally defines PWQUOTA, which indicates
        that struct passwd contains pw_quota.

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

d_quad (quadtype.U):
        This variable, if defined, tells that there's a 64-bit integer type,
        quadtype.

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

d_readdir (d_readdir.U):
        This variable conditionally defines HAS_READDIR if readdir() is
        available to read directory entries.

d_readdir64_r (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.

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

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

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

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

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

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

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

d_rewinddir (d_readdir.U):
        This variable conditionally defines HAS_REWINDDIR if rewinddir() is
        available.

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

d_rmdir (d_rmdir.U):
        This variable conditionally defines HAS_RMDIR if rmdir() is
        available to remove directories.

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

d_safebcpy (d_safebcpy.U):
        This variable conditionally defines the HAS_SAFE_BCOPY symbol if
        the bcopy() routine can do overlapping copies.  Normally, you
        should probably use memmove().

d_safemcpy (d_safemcpy.U):
        This variable conditionally defines the HAS_SAFE_MEMCPY symbol if
        the memcpy() routine can do overlapping copies.
        For overlapping copies, memmove() should be used, if available.

d_sanemcmp (d_sanemcmp.U):
        This variable conditionally defines the HAS_SANE_MEMCMP symbol if
        the memcpy() routine is available and can be used to compare relative
        magnitudes of chars with their high bits set.

d_sbrkproto (d_sbrkproto.U):
        This variable conditionally defines the 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.

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

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

d_sched_yield (d_pthread_y.U):
        This variable conditionally defines the HAS_SCHED_YIELD
        symbol if the sched_yield routine is available to yield
        the execution of the current thread.

d_scm_rights (d_socket.U):
        This variable conditionally defines the HAS_SCM_RIGHTS symbol,
        which indicates that the SCM_RIGHTS is available.  #ifdef is
        not enough because it may be an enum, glibc has been known to do this.

d_SCNfldbl (longdblfio.U):
        This variable conditionally defines the PERL_PRIfldbl symbol, which
        indicates that stdio has a symbol to scan long doubles.

d_seekdir (d_readdir.U):
        This variable conditionally defines HAS_SEEKDIR if seekdir() is
        available.

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

d_sem (d_sem.U):
        This variable conditionally defines the HAS_SEM symbol, which
        indicates that the entire sem*(2) library is present.

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

d_semctl_semid_ds (d_union_semun.U):
        This variable conditionally defines USE_SEMCTL_SEMID_DS, which
        indicates that struct semid_ds * is to be used for semctl IPC_STAT.

d_semctl_semun (d_union_semun.U):
        This variable conditionally defines USE_SEMCTL_SEMUN, which
        indicates that union semun is to be used for semctl IPC_STAT.

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

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

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

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

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

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

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

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

d_sethent (d_sethent.U):
        This variable conditionally defines HAS_SETHOSTENT if sethostent() is
        available.

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

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

d_setlinebuf (d_setlnbuf.U):
        This variable conditionally defines the 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.

d_setlocale (d_setlocale.U):
        This variable conditionally defines HAS_SETLOCALE if setlocale() is
        available to handle locale-specific ctype implementations.

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

d_setnent (d_setnent.U):
        This variable conditionally defines HAS_SETNETENT if setnetent() is
        available.

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

d_setpent (d_setpent.U):
        This variable conditionally defines HAS_SETPROTOENT if setprotoent() is
        available.

d_setpgid (d_setpgid.U):
        This variable conditionally defines the HAS_SETPGID symbol if the
        setpgid(pid, gpid) function is available to set process group ID.

d_setpgrp (d_setpgrp.U):
        This variable conditionally defines HAS_SETPGRP if setpgrp() is
        available to set the current process group.

d_setpgrp2 (d_setpgrp2.U):
        This variable conditionally defines the HAS_SETPGRP2 symbol, which
        indicates to the C program that the setpgrp2() (as in DG/UX) routine
        is available to set the current process group.

d_setprior (d_setprior.U):
        This variable conditionally defines HAS_SETPRIORITY if setpriority()
        is available to set a process's priority.

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

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

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

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

d_setregid (d_setregid.U):
        This variable conditionally defines HAS_SETREGID if setregid() is
        available to change the real and effective gid of the current
        process.

d_setresgid (d_setregid.U):
        This variable conditionally defines HAS_SETRESGID if setresgid() is
        available to change the real, effective and saved gid of the current
        process.

d_setresuid (d_setreuid.U):
        This variable conditionally defines HAS_SETREUID if setresuid() is
        available to change the real, effective and saved uid of the current
        process.

d_setreuid (d_setreuid.U):
        This variable conditionally defines HAS_SETREUID if setreuid() is
        available to change the real and effective uid of the current
        process.

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

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

d_setsent (d_setsent.U):
        This variable conditionally defines HAS_SETSERVENT if setservent() is
        available.

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

d_setsid (d_setsid.U):
        This variable conditionally defines HAS_SETSID if setsid() is
        available to set the process group ID.

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

d_shm (d_shm.U):
        This variable conditionally defines the HAS_SHM symbol, which
        indicates that the entire shm*(2) library is present.

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

d_shmatprototype (d_shmat.U):
        This variable conditionally defines the HAS_SHMAT_PROTOTYPE
        symbol, which indicates that sys/shm.h has a prototype for
        shmat.

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

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

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

d_sigaction (d_sigaction.U):
        This variable conditionally defines the HAS_SIGACTION symbol, which
        indicates that the Vr4 sigaction() routine is available.

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

d_sigprocmask (d_sigprocmask.U):
        This variable conditionally defines HAS_SIGPROCMASK
        if sigprocmask() is available to examine or change the signal mask
        of the calling process.

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

d_sin6_scope_id (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.

d_sitearch (sitearch.U):
        This variable conditionally defines 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.

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

d_sockaddr_in6 (d_socket.U):
        This variable conditionally defines the HAS_SOCKADDR_IN6 symbol, which
        indicates the availability of a struct sockaddr_in6.

d_sockaddr_sa_len (d_socket.U):
        This variable conditionally defines the HAS_SOCKADDR_SA_LEN symbol,
        which indicates that a struct sockaddr structure has the sa_len
        member.

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

d_sockatmarkproto (d_sockatmarkproto.U):
        This variable conditionally defines the 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.

d_socket (d_socket.U):
        This variable conditionally defines HAS_SOCKET, which indicates
        that the BSD socket interface is supported.

d_socklen_t (d_socklen_t.U):
        This symbol will be defined if the C compiler supports socklen_t.

d_sockpair (d_socket.U):
        This variable conditionally defines the HAS_SOCKETPAIR symbol, which
        indicates that the BSD socketpair() is supported.

d_socks5_init (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.

d_sprintf_returns_strlen (d_sprintf_len.U):
        This variable defines whether sprintf returns the length of the string
        (as per the ANSI spec). Some C libraries retain compatibility with
        pre-ANSI C and return a pointer to the passed in buffer; for these
        this variable will be undef.

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

d_srand48_r (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.

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

d_sresgproto (d_sresgproto.U):
        This variable conditionally defines the 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.

d_sresuproto (d_sresuproto.U):
        This variable conditionally defines the 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.

d_statblks (d_statblks.U):
        This variable conditionally defines USE_STAT_BLOCKS
        if this system has a stat structure declaring
        st_blksize and st_blocks.

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

d_statfs_s (d_statfs_s.U):
        This variable conditionally defines the HAS_STRUCT_STATFS symbol,
        which indicates that the struct statfs is supported.

d_static_inline (d_static_inline.U):
        This variable conditionally defines the 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.

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

d_stdio_cnt_lval (d_stdstdio.U):
        This variable conditionally defines STDIO_CNT_LVALUE if the
        FILE_cnt macro can be used as an lvalue.

d_stdio_ptr_lval (d_stdstdio.U):
        This variable conditionally defines STDIO_PTR_LVALUE if the
        FILE_ptr macro can be used as an lvalue.

d_stdio_ptr_lval_nochange_cnt (d_stdstdio.U):
        This symbol is defined if using the FILE_ptr macro as an lvalue
        to increase the pointer by n leaves File_cnt(fp) unchanged.

d_stdio_ptr_lval_sets_cnt (d_stdstdio.U):
        This symbol is defined if using the 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.

d_stdio_stream_array (stdio_streams.U):
        This variable tells whether there is an array holding
        the stdio streams.

d_stdiobase (d_stdstdio.U):
        This variable conditionally defines USE_STDIO_BASE if this system
        has a FILE structure declaring a usable _base field (or equivalent)
        in stdio.h.

d_stdstdio (d_stdstdio.U):
        This variable conditionally defines USE_STDIO_PTR if this system
        has a FILE structure declaring usable _ptr and _cnt fields (or
        equivalent) in stdio.h.

d_strchr (d_strchr.U):
        This variable conditionally defines HAS_STRCHR if strchr() and
        strrchr() are available for string searching.

d_strcoll (d_strcoll.U):
        This variable conditionally defines HAS_STRCOLL if strcoll() is
        available to compare strings using collating information.

d_strctcpy (d_strctcpy.U):
        This variable conditionally defines the USE_STRUCT_COPY symbol, which
        indicates to the C program that this C compiler knows how to copy
        structures.

d_strerrm (d_strerror.U):
        This variable holds what Strerror is defined as to translate an error
        code condition into an error message string. It could be 'strerror'
        or a more complex macro emulating strerror with sys_errlist[], or the
        "unknown" string when both strerror and sys_errlist are missing.

d_strerror (d_strerror.U):
        This variable conditionally defines HAS_STRERROR if strerror() is
        available to translate error numbers to strings.

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

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

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

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

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

d_strtol (d_strtol.U):
        This variable conditionally defines the 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.

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

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

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

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

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

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

d_strxfrm (d_strxfrm.U):
        This variable conditionally defines HAS_STRXFRM if strxfrm() is
        available to transform strings.

d_suidsafe (d_dosuid.U):
        This variable conditionally defines SETUID_SCRIPTS_ARE_SECURE_NOW
        if setuid scripts can be secure.  This test looks in /dev/fd/.

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

d_syscall (d_syscall.U):
        This variable conditionally defines HAS_SYSCALL if syscall() is
        available call arbitrary system calls.

d_syscallproto (d_syscallproto.U):
        This variable conditionally defines the 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.

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

d_sysernlst (d_strerror.U):
        This variable conditionally defines HAS_SYS_ERRNOLIST if sys_errnolist[]
        is available to translate error numbers to the symbolic name.

d_syserrlst (d_strerror.U):
        This variable conditionally defines HAS_SYS_ERRLIST if sys_errlist[] is
        available to translate error numbers to strings.

d_system (d_system.U):
        This variable conditionally defines HAS_SYSTEM if system() is
        available to issue a shell command.

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

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

d_telldir (d_readdir.U):
        This variable conditionally defines HAS_TELLDIR if telldir() is
        available.

d_telldirproto (d_telldirproto.U):
        This variable conditionally defines the 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.

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

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

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

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

d_tm_tm_gmtoff (i_time.U):
        This variable conditionally defines HAS_TM_TM_GMTOFF, which indicates
        indicates to the C program that the struct tm has the tm_gmtoff field.

d_tm_tm_zone (i_time.U):
        This variable conditionally defines HAS_TM_TM_ZONE, which indicates
        indicates to the C program that the struct tm has the tm_zone field.

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

d_truncate (d_truncate.U):
        This variable conditionally defines HAS_TRUNCATE if truncate() is
        available to truncate files.

d_trunc (d_trunc.U):
        This variable conditionally defines the HAS_TRUNCL symbol, which
        indicates to the C program that the trunc() routine is available
        to round doubles towards zero.

d_truncl (d_truncl.U):
        This variable conditionally defines the 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.

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

d_tzname (d_tzname.U):
        This variable conditionally defines HAS_TZNAME if tzname[] is
        available to access timezone names.

d_u32align (d_u32align.U):
        This variable tells whether you must access character data
        through U32-aligned pointers.

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

d_umask (d_umask.U):
        This variable conditionally defines the 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.

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

d_union_semun (d_union_semun.U):
        This variable conditionally defines HAS_UNION_SEMUN if the
        union semun is defined by including <sys/sem.h>.

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

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

d_usleep (d_usleep.U):
        This variable conditionally defines HAS_USLEEP if usleep() is
        available to do high granularity sleeps.

d_usleepproto (d_usleepproto.U):
        This variable conditionally defines the 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.

d_ustat (d_ustat.U):
        This variable conditionally defines HAS_USTAT if ustat() is
        available to query file system statistics by dev_t.

d_vendorarch (vendorarch.U):
        This variable conditionally defined PERL_VENDORARCH.

d_vendorbin (vendorbin.U):
        This variable conditionally defines PERL_VENDORBIN.

d_vendorlib (vendorlib.U):
        This variable conditionally defines PERL_VENDORLIB.

d_vendorscript (vendorscript.U):
        This variable conditionally defines PERL_VENDORSCRIPT.

d_vfork (d_vfork.U):
        This variable conditionally defines the HAS_VFORK symbol, which
        indicates the vfork() routine is available.

d_void_closedir (d_closedir.U):
        This variable conditionally defines VOID_CLOSEDIR if closedir()
        does not return a value.

d_voidsig (d_voidsig.U):
        This variable conditionally defines VOIDSIG if this system
        declares "void (*signal(...))()" in signal.h.  The old way was to
        declare it as "int (*signal(...))()".

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

d_volatile (d_volatile.U):
        This variable conditionally defines the HASVOLATILE symbol, which
        indicates to the C program that this C compiler knows about the
        volatile declaration.

d_vprintf (d_vprintf.U):
        This variable conditionally defines the HAS_VPRINTF symbol, which
        indicates to the C program that the vprintf() routine is available
        to printf with a pointer to an argument list.

d_vsnprintf (d_snprintf.U):
        This variable conditionally defines the HAS_VSNPRINTF symbol, which
        indicates to the C program that the vsnprintf () library function
        is available.

d_wait4 (d_wait4.U):
        This variable conditionally defines the HAS_WAIT4 symbol, which
        indicates the wait4() routine is available.

d_waitpid (d_waitpid.U):
        This variable conditionally defines HAS_WAITPID if waitpid() is
        available to wait for child process.

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

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

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

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

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

d_xenix (Guess.U):
        This variable conditionally defines the symbol XENIX, which alerts
        the C program that it runs under Xenix.

date (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 "date" and is not useful.

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

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

db_version_major (i_db.U):
        This variable contains the major version number of
        Berkeley DB found in the <db.h> header file.

db_version_minor (i_db.U):
        This variable contains the minor version number of
        Berkeley DB found in the <db.h> header file.
        For DB version 1 this is always 0.

db_version_patch (i_db.U):
        This variable contains the patch version number of
        Berkeley DB found in the <db.h> header file.
        For DB version 1 this is always 0.

direntrytype (i_dirent.U):
        This symbol is set to 'struct direct' or 'struct dirent' depending on
        whether dirent is available or not. You should use this pseudo type to
        portably declare your directory entries.

dlext (dlext.U):
        This variable contains the extension that is to be used for the
        dynamically loaded modules that perl generates.

dlsrc (dlsrc.U):
        This variable contains the name of the dynamic loading file that
        will be used with the package.

doublekind (doublekind.U):
        This variable, if defined, encodes the type of a double:
        1 = IEEE 754 32-bit big little endian,
        2 = IEEE 754 32-bit big big endian,
        3 = IEEE 754 64-bit big little endian,
        4 = IEEE 754 64-bit big big endian,
        5 = IEEE 754 128-bit big little endian,
        6 = IEEE 754 128-bit big big endian,
        7 = IEEE 754 64-bit big mixed endian le-be,
        8 = IEEE 754 64-bit big mixed endian be-le,
        -1 = unknown format.

doublesize (doublesize.U):
        This variable contains the value of the DOUBLESIZE symbol, which
        indicates to the C program how many bytes there are in a double.

drand01 (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 'Drand01' is mapped to drand01.

drand48_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_drand48_r
        is defined.

dtrace (usedtrace.U):
        This variable holds the location of the dtrace executable.

dynamic_ext (Extensions.U):
        This variable holds a list of XS extension files we want to
        link dynamically into the package.  It is used by Makefile.

eagain (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).

ebcdic (ebcdic.U):
        This variable conditionally defines EBCDIC if this
        system uses EBCDIC encoding.

echo (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 "echo" and is not useful.

egrep (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 "egrep" and is not useful.

emacs (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

ddgrent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endgrent_r
        is defined.

endhostent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endhostent_r
        is defined.

endnetent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endnetent_r
        is defined.

endprotoent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endprotoent_r
        is defined.

endpwent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endpwent_r
        is defined.

endservent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_endservent_r
        is defined.

eunicefix (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.

exe_ext (Unix.U):
        This is an old synonym for _exe.

expr (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 "expr" and is not useful.

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

extern_C (Csym.U):
        ANSI C requires 'extern' where C++ requires 'extern "C"'. This
        variable can be used in Configure to do the right thing.

extras (Extras.U):
        This variable holds a list of extra modules to install.

fflushall (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.

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

find (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

firstmakefile (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.

flex (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

fpossize (fpossize.U):
        This variable contains the size of a fpostype in bytes.

fpostype (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.

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

from (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 ':' if not cross-compiling.

full_ar (Loc_ar.U):
        This variable contains the full pathname to 'ar', whether or
        not the user has specified 'portability'.  This is only used
        in the Makefile.SH.

full_csh (d_csh.U):
        This variable contains the full pathname to 'csh', whether or
        not the user has specified '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
        'csh.'

full_sed (Loc_sed.U):
        This variable contains the full pathname to 'sed', whether or
        not the user has specified '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
        'sed.'

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

gccosandvers (gccvers.U):
        If 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.

gccversion (gccvers.U):
        If GNU cc (gcc) is used, this variable holds '1' or '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.

getgrent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getgrent_r
        is defined.

getgrgid_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getgrgid_r
        is defined.

getgrnam_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getgrnam_r
        is defined.

gethostbyaddr_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_gethostbyaddr_r
        is defined.

gethostbyname_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_gethostbyname_r
        is defined.

gethostent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_gethostent_r
        is defined.

getlogin_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getlogin_r
        is defined.

getnetbyaddr_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getnetbyaddr_r
        is defined.

getnetbyname_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getnetbyname_r
        is defined.

getnetent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getnetent_r
        is defined.

getprotobyname_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getprotobyname_r
        is defined.

getprotobynumber_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getprotobynumber_r
        is defined.

getprotoent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getprotoent_r
        is defined.

getpwent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getpwent_r
        is defined.

getpwnam_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getpwnam_r
        is defined.

getpwuid_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getpwuid_r
        is defined.

getservbyname_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getservbyname_r
        is defined.

getservbyport_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getservbyport_r
        is defined.

getservent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getservent_r
        is defined.

getspnam_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_getspnam_r
        is defined.

gidformat (gidf.U):
        This variable contains the format string used for printing a Gid_t.

gidsign (gidsign.U):
        This variable contains the signedness of a gidtype.
        1 for unsigned, -1 for signed.

gidsize (gidsize.U):
        This variable contains the size of a gidtype in bytes.

gidtype (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.

glibpth (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.

gmake (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 "gmake" and is not useful.

gmtime_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_gmtime_r
        is defined.

gnulibc_version (d_gnulibc.U):
        This variable contains the version number of the GNU C library.
        It is usually something like '2.2.5'.  It is a plain '' if this
        is not the GNU C library, or if the version is unknown.

grep (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 "grep" and is not useful.

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

groupstype (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.

gzip (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 "gzip" and is not useful.

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

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

hint (Oldconfig.U):
        Gives the type of hints used for previous answers. May be one of
        "default", "recommended" or "previous".

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

hostgenerate (Cross.U):
        This variable contains the path to a generate_uudmap binary that
        can be run on the host OS when cross-compiling.  Useful and
        available only during Perl build.
        Empty string '' if not cross-compiling.

hostosname (Cross.U):
        This variable contains the original value of '$^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.

hostperl (Cross.U):
        This variable contains the path to a miniperl binary that can be
        run on the host OS when cross-compiling.  Useful and available only
        during Perl build.
        Empty string '' if not cross-compiling.

html1dir (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.

html1direxp (html1dir.U):
        This variable is the same as the html1dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

html3dir (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.

html3direxp (html3dir.U):
        This variable is the same as the html3dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

i16size (perlxv.U):
        This variable is the size of an I16 in bytes.

i16type (perlxv.U):
        This variable contains the C type used for Perl's I16.

i32size (perlxv.U):
        This variable is the size of an I32 in bytes.

i32type (perlxv.U):
        This variable contains the C type used for Perl's I32.

i64size (perlxv.U):
        This variable is the size of an I64 in bytes.

i64type (perlxv.U):
        This variable contains the C type used for Perl's I64.

i8size (perlxv.U):
        This variable is the size of an I8 in bytes.

i8type (perlxv.U):
        This variable contains the C type used for Perl's I8.

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

i_assert (i_assert.U):
        This variable conditionally defines the I_ASSERT symbol, which
        indicates to the C program that <assert.h> exists and could be
        included.

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

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

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

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

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

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

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

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

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

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

i_float (i_float.U):
        This variable conditionally defines the I_FLOAT symbol, and indicates
        whether a C program may include <float.h> to get symbols like DBL_MAX
        or DBL_MIN, i.e. machine dependent floating point values.

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

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

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

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

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

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

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

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

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

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

i_limits (i_limits.U):
        This variable conditionally defines the I_LIMITS symbol, and indicates
        whether a C program may include <limits.h> to get symbols like WORD_BIT
        and friends.

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

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

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

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

i_math (i_math.U):
        This variable conditionally defines the I_MATH symbol, and indicates
        whether a C program may include <math.h>.

i_memory (i_memory.U):
        This variable conditionally defines the I_MEMORY symbol, and indicates
        whether a C program should include <memory.h>.

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

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

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

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

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

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

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

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

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

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

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

i_rpcsvcdbm (i_dbm.U):
        This variable conditionally defines the 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>.

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

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

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

i_stdarg (i_varhdr.U):
        This variable conditionally defines the I_STDARG symbol, which
        indicates to the C program that <stdarg.h> exists and should
        be included.

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

i_stddef (i_stddef.U):
        This variable conditionally defines the I_STDDEF symbol, which
        indicates to the C program that <stddef.h> exists and should
        be included.

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

i_stdlib (i_stdlib.U):
        This variable conditionally defines the I_STDLIB symbol, which
        indicates to the C program that <stdlib.h> exists and should
        be included.

i_string (i_string.U):
        This variable conditionally defines the I_STRING symbol, which
        indicates that <string.h> should be included rather than <strings.h>.

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

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

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

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

i_sysfilio (i_sysioctl.U):
        This variable conditionally defines the 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>.

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

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

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

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

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

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

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

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

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

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

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

i_sysselct (i_sysselct.U):
        This variable conditionally defines 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.

i_syssockio (i_sysioctl.U):
        This variable conditionally defines 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>.

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

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

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

i_systime (i_time.U):
        This variable conditionally defines I_SYS_TIME, which indicates
        to the C program that it should include <sys/time.h>.

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

i_systimes (i_systimes.U):
        This variable conditionally defines the I_SYS_TIMES symbol, and indicates
        whether a C program should include <sys/times.h>.

i_systypes (i_systypes.U):
        This variable conditionally defines the I_SYS_TYPES symbol,
        and indicates whether a C program should include <sys/types.h>.

i_sysuio (i_sysuio.U):
        This variable conditionally defines the I_SYSUIO symbol, and indicates
        whether a C program should include <sys/uio.h>.

i_sysun (i_sysun.U):
        This variable conditionally defines I_SYS_UN, which indicates
        to the C program that it should include <sys/un.h> to get UNIX
        domain socket definitions.

i_sysutsname (i_sysutsname.U):
        This variable conditionally defines the I_SYSUTSNAME symbol,
        and indicates whether a C program should include <sys/utsname.h>.

i_sysvfs (i_sysvfs.U):
        This variable conditionally defines the I_SYSVFS symbol,
        and indicates whether a C program should include <sys/vfs.h>.

i_syswait (i_syswait.U):
        This variable conditionally defines I_SYS_WAIT, which indicates
        to the C program that it should include <sys/wait.h>.

i_termio (i_termio.U):
        This variable conditionally defines the I_TERMIO symbol, which
        indicates to the C program that it should include <termio.h> rather
        than <sgtty.h>.

i_termios (i_termio.U):
        This variable conditionally defines the I_TERMIOS symbol, which
        indicates to the C program that the POSIX <termios.h> file is
        to be included.

i_time (i_time.U):
        This variable conditionally defines I_TIME, which indicates
        to the C program that it should include <time.h>.

i_unistd (i_unistd.U):
        This variable conditionally defines the I_UNISTD symbol, and indicates
        whether a C program should include <unistd.h>.

i_ustat (i_ustat.U):
        This variable conditionally defines the I_USTAT symbol, and indicates
        whether a C program should include <ustat.h>.

i_utime (i_utime.U):
        This variable conditionally defines the I_UTIME symbol, and indicates
        whether a C program should include <utime.h>.

i_values (i_values.U):
        This variable conditionally defines the I_VALUES symbol, and indicates
        whether a C program may include <values.h> to get symbols like MAXLONG
        and friends.

i_varargs (i_varhdr.U):
        This variable conditionally defines I_VARARGS, which indicates
        to the C program that it should include <varargs.h>.

i_varhdr (i_varhdr.U):
        Contains the name of the header to be included to get va_dcl definition.
        Typically one of varargs.h or stdarg.h.

i_vfork (i_vfork.U):
        This variable conditionally defines the I_VFORK symbol, and indicates
        whether a C program should include vfork.h.

ignore_versioned_solibs (libs.U):
        This variable should be non-empty if non-versioned shared
        libraries (libfoo.so.x.y) are to be ignored (because they
        cannot be linked against).

inc_version_list (inc_version_list.U):
        This variable specifies the list of subdirectories in over
        which perl.c:incpush() and lib/lib.pm will automatically
        search when adding directories to @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 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.

inc_version_list_init (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 PERL_INC_VERSION_LIST initialization.

incpath (usrinc.U):
        This variable must precede the normal include path to get the
        right one, as in "$incpath/usr/include" or "$incpath/usr/lib".
        Value can be "" or "/bsd43" on mips.

incpth (libpth.U):
        This variable must precede the normal include path to get the
        right one, as in "$incpath/usr/include" or "$incpath/usr/lib".
        Value can be "" or "/bsd43" on mips.

inews (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

initialinstalllocation (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 '.../', as the other binaries are found
        relative to the perl binary.

installarchlib (archlib.U):
        This variable is really the same as archlibexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installbin (bin.U):
        This variable is the same as binexp unless 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.

installhtml1dir (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.

installhtml3dir (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.

installman1dir (man1dir.U):
        This variable is really the same as man1direxp, unless you are using
        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.

installman3dir (man3dir.U):
        This variable is really the same as man3direxp, unless you are using
        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.

installprefix (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.

installprefixexp (installprefix.U):
        This variable holds the full absolute path of installprefix
        with all ~-expansion done.

installprivlib (privlib.U):
        This variable is really the same as privlibexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installscript (scriptdir.U):
        This variable is usually the same as scriptdirexp, unless you are on
        a system running AFS, in which case they may differ slightly. You
        should always use this variable within your makefiles for portability.

installsitearch (sitearch.U):
        This variable is really the same as sitearchexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installsitebin (sitebin.U):
        This variable is usually the same as sitebinexp, unless you are on
        a system running AFS, in which case they may differ slightly. You
        should always use this variable within your makefiles for portability.

installsitehtml1dir (sitehtml1dir.U):
        This variable is really the same as sitehtml1direxp, unless you are using
        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.

installsitehtml3dir (sitehtml3dir.U):
        This variable is really the same as sitehtml3direxp, unless you are using
        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.

installsitelib (sitelib.U):
        This variable is really the same as sitelibexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installsiteman1dir (siteman1dir.U):
        This variable is really the same as siteman1direxp, unless you are using
        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.

installsiteman3dir (siteman3dir.U):
        This variable is really the same as siteman3direxp, unless you are using
        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.

installsitescript (sitescript.U):
        This variable is usually the same as sitescriptexp, unless you are on
        a system running AFS, in which case they may differ slightly. You
        should always use this variable within your makefiles for portability.

installstyle (installstyle.U):
        This variable describes the "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 Config.pm.  Currently, there are only two
        styles:  "lib" and "lib/perl5".  The default library locations
        (e.g. privlib, sitelib) are either $prefix/lib or
        $prefix/lib/perl5.  The former is useful if $prefix is a
        directory dedicated to perl (e.g. /opt/perl), while the latter
        is useful if $prefix is shared by many packages, e.g. if
        $prefix=/usr/local.

        Unfortunately, while this "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 /opt/perl, but $siteprefix might be /usr/local.
        (Perhaps, in retrospect, the "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 PREFIX on
        the Makefile.PL command line), then there is no reason to
        assume that the Configure-time $installstyle setting will be
        relevant for that PREFIX.

        This may later be extended to include other information, so
        be careful with pattern-matching on the results.

        For compatibility with perl5.005 and earlier, the default
        setting is based on whether or not $prefix contains the string
        "perl".

installusrbinperl (instubperl.U):
        This variable tells whether Perl should be installed also as
        /usr/bin/perl in addition to
        $installbin/perl

installvendorarch (vendorarch.U):
        This variable is really the same as vendorarchexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorbin (vendorbin.U):
        This variable is really the same as vendorbinexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorhtml1dir (vendorhtml1dir.U):
        This variable is really the same as vendorhtml1direxp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorhtml3dir (vendorhtml3dir.U):
        This variable is really the same as vendorhtml3direxp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorlib (vendorlib.U):
        This variable is really the same as vendorlibexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorman1dir (vendorman1dir.U):
        This variable is really the same as vendorman1direxp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorman3dir (vendorman3dir.U):
        This variable is really the same as vendorman3direxp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

installvendorscript (vendorscript.U):
        This variable is really the same as vendorscriptexp but may differ on
        those systems using AFS. For extra portability, only this variable
        should be used in makefiles.

intsize (intsize.U):
        This variable contains the value of the INTSIZE symbol, which
        indicates to the C program how many bytes there are in an int.

issymlink (issymlink.U):
        This variable holds the test command to test for a symbolic link
        (if they are supported).  Typical values include 'test -h' and
        'test -L'.

ivdformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl IV as a signed decimal integer.

ivsize (perlxv.U):
        This variable is the size of an IV in bytes.

ivtype (perlxv.U):
        This variable contains the C type used for Perl's IV.

known_extensions (Extensions.U):
        This variable holds a list of all extensions (both 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 "extensions" for the list of extensions
        actually built and available.

ksh (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

ld (dlsrc.U):
        This variable indicates the program to be used to link
        libraries for dynamic loading.  On some systems, it is 'ld'.
        On ELF systems, it should be $cc.  Mostly, we'll try to respect
        the hint file setting.

ld_can_script (dlsrc.U):
        This variable shows if the loader accepts scripts in the form of
        -Wl,--version-script=ld.script. This is currently only supported
        for GNU ld on ELF in dynamic loading builds.

lddlflags (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 '-b'.  For sunos 4.1, it is empty.

ldflags (ccflags.U):
        This variable contains any additional C loader flags desired by
        the user.  It is up to the Makefile to use this.

ldflags_uselargefiles (uselfs.U):
        This variable contains the loader flags needed by large file builds
        and added to ldflags by hints files.

ldlibpthname (libperl.U):
        This variable holds the name of the shared library
        search path, often LD_LIBRARY_PATH.  To get an empty
        string, the hints file must set this to 'none'.

less (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 "less" and is not useful.

lib_ext (Unix.U):
        This is an old synonym for _a.

libc (libc.U):
        This variable contains the location of the C library.

libperl (libperl.U):
        The perl executable is obtained by linking perlmain.c with
        libperl, any static extensions (usually just DynaLoader),
        and any other libraries needed on this system.  libperl
        is usually libperl.a, but can also be libperl.so.xxx if
        the user wishes to build a perl executable with a shared
        library.

libpth (libpth.U):
        This variable holds the general path (space-separated) used to find
        libraries. It is intended to be used by other units.

libs (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.

libsdirs (libs.U):
        This variable holds the directory names aka dirnames of the libraries
        we found and accepted, duplicates are removed.

libsfiles (libs.U):
        This variable holds the filenames aka basenames of the libraries
        we found and accepted.

libsfound (libs.U):
        This variable holds the full pathnames of the libraries
        we found and accepted.

libspath (libs.U):
        This variable holds the directory names probed for libraries.

libswanted (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.

libswanted_uselargefiles (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 "lib" prefix or any suffix, just
        like libswanted..

line (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

lint (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

lkflags (ccflags.U):
        This variable contains any additional C partial linker flags desired by
        the user.  It is up to the Makefile to use this.

ln (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 "ln" and is not useful.

lns (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 'ln -s' or 'ln'

localtime_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_localtime_r
        is defined.

locincpth (ccflags.U):
        This variable contains a list of additional directories to be
        searched by the compiler.  The appropriate '-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 libpth.U.

loclibpth (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.

longdblkind (d_longdbl.U):
        This variable, if defined, encodes the type of a long double:
        0 = double, 1 = IEEE 754 128-bit big little endian,
        2 = IEEE 754 128-bit big 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, -1 = unknown format.

longdblsize (d_longdbl.U):
        This variable contains the value of the LONG_DOUBLESIZE symbol, which
        indicates to the C program how many bytes there are in a long double,
        if this system supports long doubles.

longlongsize (d_longlong.U):
        This variable contains the value of the LONGLONGSIZE symbol, which
        indicates to the C program how many bytes there are in a long long,
        if this system supports long long.

longsize (intsize.U):
        This variable contains the value of the LONGSIZE symbol, which
        indicates to the C program how many bytes there are in a long.

lp (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

lpr (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

ls (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 "ls" and is not useful.

lseeksize (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).

lseektype (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).

mail (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

mailx (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

make (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 "make" and is not useful.

make_set_make (make.U):
        Some versions of 'make' set the variable MAKE.  Others do not.
        This variable contains the string to be included in Makefile.SH
        so that MAKE is set if needed, and not if not needed.
        Possible values are:

        make_set_make='#'               # If your make program handles this for you,

        make_set_make="MAKE=$make"      # if it doesn't.

        This uses a comment character so that we can distinguish a
        'set' value (from a previous config.sh or Configure '-D' option)
        from an uncomputed value.

mallocobj (mallocsrc.U):
        This variable contains the name of the malloc.o that this package
        generates, if that malloc.o is preferred over the system malloc.
        Otherwise the value is null.  This variable is intended for generating
        Makefiles.  See mallocsrc.

mallocsrc (mallocsrc.U):
        This variable contains the name of the malloc.c that comes with
        the package, if that malloc.c is preferred over the system malloc.
        Otherwise the value is null.  This variable is intended for generating
        Makefiles.

malloctype (mallocsrc.U):
        This variable contains the kind of ptr returned by malloc and realloc.

man1dir (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
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~name expansion yourself.

man1direxp (man1dir.U):
        This variable is the same as the man1dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

man1ext (man1dir.U):
        This variable contains the extension that the manual page should
        have: one of 'n', 'l', or '1'.  The Makefile must supply the '.'.
        See man1dir.

man3dir (man3dir.U):
        This variable contains the name of the directory in which manual
        source pages are to be put.  It is the responsibility of the
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~name expansion yourself.

man3direxp (man3dir.U):
        This variable is the same as the man3dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

man3ext (man3dir.U):
        This variable contains the extension that the manual page should
        have: one of 'n', 'l', or '3'.  The Makefile must supply the '.'.
        See man3dir.

mips_type (usrinc.U):
        This variable holds the environment type for the mips system.
        Possible values are "BSD 4.3" and "System V".

mistrustnm (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 "compile", a test program will be compiled to try to
        find any symbol that can't be located via nm lookup.  If mistrustnm is
        "run", the test program will be run as well as being compiled.

mkdir (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 "mkdir" and is not useful.

mmaptype (d_mmap.U):
        This symbol contains the type of pointer returned by mmap()
        (and simultaneously the type of the first argument).
        It can be 'void *' or 'caddr_t'.

modetype (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.

more (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 "more" and is not useful.

multiarch (multiarch.U):
        This variable conditionally defines the MULTIARCH symbol
        which signifies the presence of multiplatform files.
        This is normally set by hints files.

mv (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

myarchname (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.

mydomain (myhostname.U):
        This variable contains the eventual value of the 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.

myhostname (myhostname.U):
        This variable contains the eventual value of the 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.

myuname (Oldconfig.U):
        The output of 'uname -a' if available, otherwise the hostname.
        The whole thing is then lower-cased and slashes and single quotes are
        removed.

n (n.U):
        This variable contains the '-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".

need_va_copy (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, handy.h defines a platform-
        independent macro, Perl_va_copy(src, dst), to do the job.

netdb_hlen_type (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.

netdb_host_type (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.

netdb_name_type (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.

netdb_net_type (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.

nm (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 "nm" and is not useful.

nm_opt (usenm.U):
        This variable holds the options that may be necessary for nm.

nm_so_opt (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 ELF library which
        has been stripped, but nm --dynamic is *fatal* on an archive library.
        Maybe Linux should just always set usenm=false.

nonxs_ext (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 VMS specific extension).

nroff (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 "nroff" and is not useful.

nv_overflows_integers_at (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.

nv_preserves_uv_bits (perlxv.U):
        This variable indicates how many of bits type uvtype
        a variable nvtype can preserve.

nveformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %e-ish floating point format.

nvEUformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %E-ish floating point format.

nvfformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %f-ish floating point format.

nvFUformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %F-ish floating point format.

nvgformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %g-ish floating point format.

nvGUformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl NV using %G-ish floating point format.

nvsize (perlxv.U):
        This variable is the size of an NV in bytes.

nvtype (perlxv.U):
        This variable contains the C type used for Perl's NV.

o_nonblock (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(FIOSNBIO) instead,
        but that is only supported by some devices.

obj_ext (Unix.U):
        This is an old synonym for _o.

old_pthread_create_joinable (d_pthrattrj.U):
        This variable defines the constant to use for creating joinable
        (aka undetached) pthreads.  Unused if pthread.h defines
        PTHREAD_CREATE_JOINABLE.  If used, possible values are
        PTHREAD_CREATE_UNDETACHED and __UNDETACHED.

optimize (ccflags.U):
        This variable contains any optimizer/debugger flag that should be used.
        It is up to the Makefile to use it.

orderlib (orderlib.U):
        This variable is "true" if the components of libraries must be ordered
        (with `lorder $* | tsort`) before placing them in an archive.  Set to
        "false" if ranlib or ar can generate random libraries.

osname (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.

osvers (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 os_4.0 or
        os_4.1, etc., not keeping separate files for each little release.

otherlibdirs (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 @INC.
        Perl will automatically search below each path for version-
        and architecture-specific directories.  See inc_version_list
        for more details.
        A value of ' ' means 'none' and is used to preserve this value
        for the next run through Configure.

package (package.U):
        This variable contains the name of the package being constructed.
        It is primarily intended for the use of later Configure units.

pager (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.

passcat (nis.U):
        This variable contains a command that produces the text of the
        /etc/passwd file.  This is normally "cat /etc/passwd", but can be
        "ypcat passwd" when NIS is used.
        On some systems, such as os390, there may be no equivalent
        command, in which case this variable is unset.

patchlevel (patchlevel.U):
        The patchlevel level of this package.
        The value of patchlevel comes from the patchlevel.h file.
        In a version number such as 5.6.1, this is the "6".
        In patchlevel.h, this is referred to as "PERL_VERSION".

path_sep (Unix.U):
        This is an old synonym for p_ in Head.U, the character
        used to separate elements in the command shell search PATH.

perl (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 "perl" and is not useful.

perl5 (perl5.U):
        This variable contains the full path (if any) to a previously
        installed perl5.005 or later suitable for running the script
        to determine inc_version_list.

PERL_API_REVISION (patchlevel.h):
        This number describes the earliest compatible PERL_REVISION of
        Perl ("compatibility" here being defined as sufficient binary/API
        compatibility to run XS code built with the older version).
        Normally this does not change across maintenance releases.
        Please read the comment in patchlevel.h.

PERL_API_SUBVERSION (patchlevel.h):
        This number describes the earliest compatible PERL_SUBVERSION of
        Perl ("compatibility" here being defined as sufficient binary/API
        compatibility to run XS code built with the older version).
        Normally this does not change across maintenance releases.
        Please read the comment in patchlevel.h.

PERL_API_VERSION (patchlevel.h):
        This number describes the earliest compatible PERL_VERSION of
        Perl ("compatibility" here being defined as sufficient binary/API
        compatibility to run XS code built with the older version).
        Normally this does not change across maintenance releases.
        Please read the comment in patchlevel.h.

PERL_CONFIG_SH (Oldsyms.U):
        This is set to 'true' in config.sh so that a shell script
        sourcing config.sh can tell if it has been sourced already.

PERL_PATCHLEVEL (Oldsyms.U):
        This symbol reflects the patchlevel, if available. Will usually
        come from the .patch file, which is available when the perl
        source tree was fetched with rsync.

perl_patchlevel (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.

PERL_REVISION (Oldsyms.U):
        In a Perl version number such as 5.6.2, this is the 5.
        This value is manually set in patchlevel.h

perl_static_inline (d_static_inline.U):
        This variable defines the 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     (MSVC)
        static _inline      (older MSVC)
        static              (c89 compilers)

PERL_SUBVERSION (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 patchlevel.h

PERL_VERSION (Oldsyms.U):
        In a Perl version number such as 5.6.2, this is the 6.
        This value is manually set in patchlevel.h

perladmin (perladmin.U):
        Electronic mail address of the perl5 administrator.

perllibs (End.U):
        The list of libraries needed by Perl only (any libraries needed
        by extensions only will by dropped, if using dynamic loading).

perlpath (perlpath.U):
        This variable contains the eventual value of the PERLPATH symbol,
        which contains the name of the perl interpreter to be used in
        shell scripts and in the "eval '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.

pg (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 "pg" and is not useful.

phostname (myhostname.U):
        This variable contains the eventual value of the 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.

pidtype (pidtype.U):
        This variable defines PIDTYPE to be something like pid_t, int,
        ushort, or whatever type is used to declare process ids in the kernel.

plibpth (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.

pmake (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

pr (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

prefix (prefix.U):
        This variable holds the name of the directory below which the
        user will install the package.  Usually, this is /usr/local, and
        executables go in /usr/local/bin, library stuff in /usr/local/lib,
        man pages in /usr/local/man, etc.  It is only used to set defaults
        for things in bin.U, mansrc.U, privlib.U, or scriptdir.U.

prefixexp (prefix.U):
        This variable holds the full absolute path of the directory below
        which the user will install the package.  Derived from prefix.

privlib (privlib.U):
        This variable contains the eventual value of the PRIVLIB symbol,
        which is the name of the private library for this package.  It may
        have a ~ on the front. It is up to the makefile to eventually create
        this directory while performing installation (with ~ substitution).

privlibexp (privlib.U):
        This variable is the ~name expanded version of privlib, so that you
        may use it directly in Makefiles or shell scripts.

procselfexe (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.

prototype (prototype.U):
        This variable holds the eventual value of CAN_PROTOTYPE, which
        indicates the C compiler can handle function prototypes.

ptrsize (ptrsize.U):
        This variable contains the value of the PTRSIZE symbol, which
        indicates to the C program how many bytes there are in a pointer.

quadkind (quadtype.U):
        This variable, if defined, encodes the type of a quad:
        1 = int, 2 = long, 3 = long long, 4 = int64_t.

quadtype (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.

randbits (randfunc.U):
        Indicates how many bits are produced by the function used to
        generate normalized random numbers.

randfunc (randfunc.U):
        Indicates the name of the random number function to use.
        Values include drand48, random, and rand. In C programs,
        the 'Drand01' macro is defined to generate uniformly distributed
        random numbers over the range [0., 1.[ (see drand01 and nrand).

random_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_random_r
        is defined.

randseedtype (randfunc.U):
        Indicates the type of the argument of the seedfunc.

ranlib (orderlib.U):
        This variable is set to the pathname of the ranlib program, if it is
        needed to generate random libraries.  Set to ":" if ar can generate
        random libraries or if random libraries are not supported

rd_nodata (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 O_NDELAY is
        used, which is a shame because you cannot make the difference between
        no data and an EOF.. Sigh!

readdir64_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_readdir64_r
        is defined.

readdir_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_readdir_r
        is defined.

revision (patchlevel.U):
        The value of revision comes from the patchlevel.h file.
        In a version number such as 5.6.1, this is the "5".
        In patchlevel.h, this is referred to as "PERL_REVISION".

rm (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 "rm" and is not useful.

rm_try (Unix.U):
        This is a cleanup variable for try test programs.
        Internal Configure use only.

rmail (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

run (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.

runnm (usenm.U):
        This variable contains 'true' or '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.

sched_yield (d_pthread_y.U):
        This variable defines the way to yield the execution
        of the current thread.

scriptdir (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 /usr/share. Programs
        must be prepared to deal with ~name expansion.

scriptdirexp (scriptdir.U):
        This variable is the same as scriptdir, but is filename expanded
        at configuration time, for programs not wanting to bother with it.

sed (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 "sed" and is not useful.

seedfunc (randfunc.U):
        Indicates the random number generating seed function.
        Values include srand48, srandom, and srand.

selectminbits (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(n/32), especially many little-endians do
        the latter.  This is only useful if you have select(), naturally.

selecttype (selecttype.U):
        This variable holds the type used for the 2nd, 3rd, and 4th
        arguments to select.  Usually, this is 'fd_set *', if HAS_FD_SET
        is defined, and 'int *' otherwise.  This is only useful if you
        have select(), naturally.

sendmail (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

setgrent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setgrent_r
        is defined.

sethostent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_sethostent_r
        is defined.

setlocale_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setlocale_r
        is defined.

setnetent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setnetent_r
        is defined.

setprotoent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setprotoent_r
        is defined.

setpwent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setpwent_r
        is defined.

setservent_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_setservent_r
        is defined.

sGMTIME_max (time_size.U):
        This variable defines the maximum value of the time_t offset that
        the system function gmtime () accepts

sGMTIME_min (time_size.U):
        This variable defines the minimum value of the time_t offset that
        the system function gmtime () accepts

sh (sh.U):
        This variable contains the full pathname of the shell used
        on this system to execute Bourne shell scripts.  Usually, this will be
        /bin/sh, though it's possible that some systems will have /bin/ksh,
        /bin/pdksh, /bin/ash, /bin/bash, or even something such as
        D:/bin/sh.exe.
        This unit comes before Options.U, so you can't set sh with a '-D'
        option, though you can override this (and startsh)
        with '-O -Dsh=/bin/whatever -Dstartsh=whatever'

shar (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

sharpbang (spitshell.U):
        This variable contains the string #! if this system supports that
        construct.

shmattype (d_shmat.U):
        This symbol contains the type of pointer returned by shmat().
        It can be 'void *' or 'char *'.

shortsize (intsize.U):
        This variable contains the value of the SHORTSIZE symbol which
        indicates to the C program how many bytes there are in a short.

shrpenv (libperl.U):
        If the user builds a shared libperl.so, then we need to tell the
        'perl' executable where it will be able to find the installed libperl.so.
        One way to do this on some systems is to set the environment variable
        LD_RUN_PATH to the directory that will be the final location of the
        shared libperl.so.  The makefile can use this with something like
        $shrpenv $(CC) -o perl perlmain.o $libperl $libs
        Typical values are
        shrpenv="env LD_RUN_PATH=$archlibexp/CORE"
        or
        shrpenv=''
        See the main perl Makefile.SH for actual working usage.
        Alternatively, we might be able to use a command line option such
        as -R $archlibexp/CORE (Solaris) or -Wl,-rpath
        $archlibexp/CORE (Linux).

shsharp (spitshell.U):
        This variable tells further Configure units whether your sh can
        handle # comments.

sig_count (sig_name.U):
        This variable holds a number larger than the largest valid
        signal number.  This is usually the same as the NSIG macro.

sig_name (sig_name.U):
        This variable holds the signal names, space separated. The leading
        SIG in signal name is removed.  A ZERO is prepended to the list.
        This is currently not used, sig_name_init is used instead.

sig_name_init (sig_name.U):
        This variable holds the signal names, enclosed in double quotes and
        separated by commas, suitable for use in the SIG_NAME definition
        below.  A "ZERO" is prepended to the list, and the list is
        terminated with a plain 0.  The leading SIG in signal names
        is removed. See sig_num.

sig_num (sig_name.U):
        This variable holds the signal numbers, space separated. A ZERO is
        prepended to the list (corresponding to the fake 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.

sig_num_init (sig_name.U):
        This variable holds the signal numbers, enclosed in double quotes and
        separated by commas, suitable for use in the SIG_NUM definition
        below.  A "ZERO" is prepended to the list, and the list is
        terminated with a plain 0.

sig_size (sig_name.U):
        This variable contains the number of elements of the sig_name
        and sig_num arrays.

signal_t (d_voidsig.U):
        This variable holds the type of the signal handler (void or int).

sitearch (sitearch.U):
        This variable contains the eventual value of the SITEARCH symbol,
        which is the name of the private library for this package.  It may
        have a ~ on the front. It is up to the makefile to eventually create
        this directory while performing installation (with ~ 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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitearchexp (sitearch.U):
        This variable is the ~name expanded version of sitearch, so that you
        may use it directly in Makefiles or shell scripts.

sitebin (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 /usr/local/bin. Programs using
        this variable must be prepared to deal with ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitebinexp (sitebin.U):
        This is the same as the sitebin variable, but is filename expanded at
        configuration time, for use in your makefiles.

sitehtml1dir (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
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitehtml1direxp (sitehtml1dir.U):
        This variable is the same as the sitehtml1dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

sitehtml3dir (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
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitehtml3direxp (sitehtml3dir.U):
        This variable is the same as the sitehtml3dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

sitelib (sitelib.U):
        This variable contains the eventual value of the SITELIB symbol,
        which is the name of the private library for this package.  It may
        have a ~ on the front. It is up to the makefile to eventually create
        this directory while performing installation (with ~ 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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitelib_stem (sitelib.U):
        This variable is $sitelibexp with any trailing version-specific component
        removed.  The elements in inc_version_list (inc_version_list.U) can
        be tacked onto this variable to generate a list of directories to search.

sitelibexp (sitelib.U):
        This variable is the ~name expanded version of sitelib, so that you
        may use it directly in Makefiles or shell scripts.

siteman1dir (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
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

siteman1direxp (siteman1dir.U):
        This variable is the same as the siteman1dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

siteman3dir (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
        Makefile.SH to get the value of this into the proper command.
        You must be prepared to do the ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

siteman3direxp (siteman3dir.U):
        This variable is the same as the siteman3dir variable, but is filename
        expanded at configuration time, for convenient use in makefiles.

siteprefix (siteprefix.U):
        This variable holds the full absolute path of the directory below
        which the user will install add-on packages.
        See INSTALL for usage and examples.

siteprefixexp (siteprefix.U):
        This variable holds the full absolute path of the directory below
        which the user will install add-on packages.  Derived from siteprefix.

sitescript (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 /usr/local/bin. Programs using
        this variable must be prepared to deal with ~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 Makefile.PL
        or equivalent.  See INSTALL for details.

sitescriptexp (sitescript.U):
        This is the same as the sitescript variable, but is filename expanded at
        configuration time, for use in your makefiles.

sizesize (sizesize.U):
        This variable contains the size of a sizetype in bytes.

sizetype (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.

sleep (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

sLOCALTIME_max (time_size.U):
        This variable defines the maximum value of the time_t offset that
        the system function localtime () accepts

sLOCALTIME_min (time_size.U):
        This variable defines the minimum value of the time_t offset that
        the system function localtime () accepts

smail (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

so (so.U):
        This variable holds the extension used to identify shared libraries
        (also known as shared objects) on the system. Usually set to 'so'.

sockethdr (d_socket.U):
        This variable has any cpp '-I' flags needed for socket support.

socketlib (d_socket.U):
        This variable has the names of any libraries needed for socket support.

socksizetype (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.

sort (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 "sort" and is not useful.

spackage (package.U):
        This variable contains the name of the package being constructed,
        with the first letter uppercased, i.e. suitable for starting
        sentences.

spitshell (spitshell.U):
        This variable contains the command necessary to spit out a runnable
        shell on this system.  It is either cat or a grep '-v' for # comments.

sPRId64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit decimal numbers (format 'd') for output.

sPRIeldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'e') for output.

sPRIEUldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'E') for output.
        The 'U' in the name is to separate this from sPRIeldbl so that even
        case-blind systems can see the difference.

sPRIfldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'f') for output.

sPRIFUldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'F') for output.
        The 'U' in the name is to separate this from sPRIfldbl so that even
        case-blind systems can see the difference.

sPRIgldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'g') for output.

sPRIGUldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'G') for output.
        The 'U' in the name is to separate this from sPRIgldbl so that even
        case-blind systems can see the difference.

sPRIi64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit decimal numbers (format 'i') for output.

sPRIo64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit octal numbers (format 'o') for output.

sPRIu64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit unsigned decimal numbers (format 'u') for output.

sPRIx64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit hexadecimal numbers (format 'x') for output.

sPRIXU64 (quadfio.U):
        This variable, if defined, contains the string used by stdio to
        format 64-bit hExADECimAl numbers (format 'X') for output.
        The 'U' in the name is to separate this from sPRIx64 so that even
        case-blind systems can see the difference.

srand48_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_srand48_r
        is defined.

srandom_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_srandom_r
        is defined.

src (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 VPATH accordingly
        to find the sources remotely.  Use $pkgsrc to have an absolute path.

sSCNfldbl (longdblfio.U):
        This variable, if defined, contains the string used by stdio to
        format long doubles (format 'f') for input.

ssizetype (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).

st_ino_sign (st_ino_def.U):
        This variable contains the signedness of struct stat's st_ino.
        1 for unsigned, -1 for signed.

st_ino_size (st_ino_def.U):
        This variable contains the size of struct stat's st_ino in bytes.

startperl (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 ${1+"$@"}'
        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.

startsh (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.

static_ext (Extensions.U):
        This variable holds a list of XS extension files we want to
        link statically into the package.  It is used by Makefile.

stdchar (stdchar.U):
        This variable conditionally defines STDCHAR to be the type of char
        used in stdio.h.  It has the values "unsigned char" or "char".

stdio_base (d_stdstdio.U):
        This variable defines how, given a FILE pointer, fp, to access the
        _base field (or equivalent) of stdio.h's FILE structure.  This will
        be used to define the macro FILE_base(fp).

stdio_bufsiz (d_stdstdio.U):
        This variable defines how, given a FILE pointer, fp, to determine
        the number of bytes store in the I/O buffer pointer to by the
        _base field (or equivalent) of stdio.h's FILE structure.  This will
        be used to define the macro FILE_bufsiz(fp).

stdio_cnt (d_stdstdio.U):
        This variable defines how, given a FILE pointer, fp, to access the
        _cnt field (or equivalent) of stdio.h's FILE structure.  This will
        be used to define the macro FILE_cnt(fp).

stdio_filbuf (d_stdstdio.U):
        This variable defines how, given a FILE pointer, fp, to tell
        stdio to refill its internal buffers (?).  This will
        be used to define the macro FILE_filbuf(fp).

stdio_ptr (d_stdstdio.U):
        This variable defines how, given a FILE pointer, fp, to access the
        _ptr field (or equivalent) of stdio.h's FILE structure.  This will
        be used to define the macro FILE_ptr(fp).

stdio_stream_array (stdio_streams.U):
        This variable tells the name of the array holding the stdio streams.
        Usual values include _iob, __iob, and __sF.

strerror_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_strerror_r
        is defined.

strings (i_string.U):
        This variable holds the full path of the string header that will be
        used. Typically /usr/include/string.h or /usr/include/strings.h.

submit (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

subversion (patchlevel.U):
        The subversion level of this package.
        The value of subversion comes from the patchlevel.h file.
        In a version number such as 5.6.1, this is the "1".
        In patchlevel.h, this is referred to as "PERL_SUBVERSION".
        This is unique to perl.

sysman (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.

sysroot (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.

tail (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

tar (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

targetarch (Cross.U):
        If cross-compiling, this variable contains the target architecture.
        If not, this will be empty.

targetdir (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 '/tmp' if not set.

targetenv (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.

targethost (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.

targetmkdir (Cross.U):
        This variable contains the command used by Configure to create a
        new directory on the target host.

targetport (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.

targetsh (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.

tbl (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

tee (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

test (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 "test" and is not useful.

timeincl (i_time.U):
        This variable holds the full path of the included time header(s).

timetype (d_time.U):
        This variable holds the type returned by time(). It can be long,
        or time_t on BSD sites (in which case <sys/types.h> should be
        included). Anyway, the type Time_t should be used.

tmpnam_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_tmpnam_r
        is defined.

to (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 ':' if not cross-compiling.

touch (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 "touch" and is not useful.

tr (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 "tr" and is not useful.

trnl (trnl.U):
        This variable contains the value to be passed to the tr(1)
        command to transliterate a newline.  Typical values are
        '\012' and '\n'.  This is needed for EBCDIC systems where
        newline is not necessarily '\012'.

troff (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

ttyname_r_proto (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
        REENTRANT_PROTO_T_ABC macros of reentr.h if d_ttyname_r
        is defined.

u16size (perlxv.U):
        This variable is the size of an U16 in bytes.

u16type (perlxv.U):
        This variable contains the C type used for Perl's U16.

u32size (perlxv.U):
        This variable is the size of an U32 in bytes.

u32type (perlxv.U):
        This variable contains the C type used for Perl's U32.

u64size (perlxv.U):
        This variable is the size of an U64 in bytes.

u64type (perlxv.U):
        This variable contains the C type used for Perl's U64.

u8size (perlxv.U):
        This variable is the size of an U8 in bytes.

u8type (perlxv.U):
        This variable contains the C type used for Perl's U8.

uidformat (uidf.U):
        This variable contains the format string used for printing a Uid_t.

uidsign (uidsign.U):
        This variable contains the signedness of a uidtype.
        1 for unsigned, -1 for signed.

uidsize (uidsize.U):
        This variable contains the size of a uidtype in bytes.

uidtype (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.

uname (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 "uname" and is not useful.

uniq (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 "uniq" and is not useful.

uquadtype (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.

use5005threads (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.

use64bitall (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 CPU at all or
        you may need at least to reboot your OS to 64-bit mode.

use64bitint (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.

usecbacktrace (usebacktrace.U):
        This variable indicates whether we are compiling with backtrace
        support.

usecrosscompile (Cross.U):
        This variable conditionally defines the USE_CROSS_COMPILE symbol,
        and indicates that Perl has been cross-compiled.

usedevel (Devel.U):
        This variable indicates that Perl was configured with development
        features enabled.  This should not be done for production builds.

usedl (dlsrc.U):
        This variable indicates if the system supports dynamic
        loading of some sort.  See also dlsrc and dlobj.

usedtrace (usedtrace.U):
        This variable indicates whether we are compiling with dtrace
        support. See also dtrace.

usefaststdio (usefaststdio.U):
        This variable conditionally defines the USE_FAST_STDIO symbol,
        and indicates that Perl should be built to use 'fast stdio'.
        Defaults to define in Perls 5.8 and earlier, to undef later.

useithreads (usethreads.U):
        This variable conditionally defines the USE_ITHREADS symbol,
        and indicates that Perl should be built to use the interpreter-based
        threading implementation.

usekernprocpathname (usekernprocpathname.U):
        This variable, indicates that we can use sysctl with
        KERN_PROC_PATHNAME to get a full path for the executable, and hence
        convert $^X to an absolute path.

uselargefiles (uselfs.U):
        This variable conditionally defines the USE_LARGE_FILES symbol,
        and indicates that large file interfaces should be used when
        available.

uselongdouble (uselongdbl.U):
        This variable conditionally defines the USE_LONG_DOUBLE symbol,
        and indicates that long doubles should be used when available.

usemallocwrap (mallocsrc.U):
        This variable contains y if we are wrapping malloc to prevent
        integer overflow during size calculations.

usemorebits (usemorebits.U):
        This variable conditionally defines the USE_MORE_BITS symbol,
        and indicates that explicit 64-bit interfaces and long doubles
        should be used when available.

usemultiplicity (usemultiplicity.U):
        This variable conditionally defines the MULTIPLICITY symbol,
        and indicates that Perl should be built to use multiplicity.

usemymalloc (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 'y', then -lmalloc is removed from $libs.

usenm (usenm.U):
        This variable contains 'true' or 'false' depending whether the
        nm extraction is wanted or not.

usensgetexecutablepath (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.

useopcode (Extensions.U):
        This variable holds either 'true' or '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.

useperlio (useperlio.U):
        This variable conditionally defines the USE_PERLIO symbol,
        and indicates that the PerlIO abstraction should be
        used throughout.

useposix (Extensions.U):
        This variable holds either 'true' or 'false' to indicate
        whether the POSIX extension should be used.  The sole
        use for this currently is to allow an easy mechanism
        for hints files to indicate that POSIX will not compile
        on a particular system.

usequadmath (usequadmath.U):
        This variable conditionally defines the USE_QUADMATH symbol,
        and indicates that the quadmath library __float128 long doubles
        should be used when available.

usereentrant (usethreads.U):
        This variable conditionally defines the 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.

userelocatableinc (bin.U):
        This variable is set to true to indicate that perl should relocate
        @INC entries at runtime based on the path to the perl binary.
        Any @INC paths starting ".../" 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 "dir/../" pairs)

useshrplib (libperl.U):
        This variable is set to 'true' if the user wishes
        to build a shared libperl, and 'false' otherwise.

usesitecustomize (d_sitecustomize.U):
        This variable is set to true when the user requires a mechanism that
        allows the sysadmin to add entries to @INC at runtime.  This variable
        being set, makes perl run '$sitelib/sitecustomize.pl' at startup.

usesocks (usesocks.U):
        This variable conditionally defines the USE_SOCKS symbol,
        and indicates that Perl should be built to use SOCKS.

usethreads (usethreads.U):
        This variable conditionally defines the USE_THREADS symbol,
        and indicates that Perl should be built to use threads.

usevendorprefix (vendorprefix.U):
        This variable tells whether the vendorprefix
        and consequently other vendor* paths are in use.

useversionedarchname (archname.U):
        This variable indicates whether to include the $api_versionstring
        as a component of the $archname.

usevfork (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.

usrinc (usrinc.U):
        This variable holds the path of the include files, which is
        usually /usr/include. It is mainly used by other Configure units.

uuname (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

uvoformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl UV as an unsigned octal integer.

uvsize (perlxv.U):
        This variable is the size of a UV in bytes.

uvtype (perlxv.U):
        This variable contains the C type used for Perl's UV.

uvuformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl UV as an unsigned decimal integer.

uvxformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl UV as an unsigned hexadecimal integer in lowercase abcdef.

uvXUformat (perlxvf.U):
        This variable contains the format string used for printing
        a Perl UV as an unsigned hexadecimal integer in uppercase ABCDEF.

vaproto (vaproto.U):
        This variable conditionally defines CAN_VAPROTO on systems supporting
        prototype declaration of functions with a variable number of
        arguments. See also prototype.

vendorarch (vendorarch.U):
        This variable contains the value of the PERL_VENDORARCH symbol.
        It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorarchexp (vendorarch.U):
        This variable is the ~name expanded version of vendorarch, so that you
        may use it directly in Makefiles or shell scripts.

vendorbin (vendorbin.U):
        This variable contains the eventual value of the VENDORBIN symbol.
        It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorbinexp (vendorbin.U):
        This variable is the ~name expanded version of vendorbin, so that you
        may use it directly in Makefiles or shell scripts.

vendorhtml1dir (vendorhtml1dir.U):
        This variable contains the name of the directory for html
        pages.  It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorhtml1direxp (vendorhtml1dir.U):
        This variable is the ~name expanded version of vendorhtml1dir, so that you
        may use it directly in Makefiles or shell scripts.

vendorhtml3dir (vendorhtml3dir.U):
        This variable contains the name of the directory for html
        library pages.  It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorhtml3direxp (vendorhtml3dir.U):
        This variable is the ~name expanded version of vendorhtml3dir, so that you
        may use it directly in Makefiles or shell scripts.

vendorlib (vendorlib.U):
        This variable contains the eventual value of the 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorlib_stem (vendorlib.U):
        This variable is $vendorlibexp with any trailing version-specific component
        removed.  The elements in inc_version_list (inc_version_list.U) can
        be tacked onto this variable to generate a list of directories to search.

vendorlibexp (vendorlib.U):
        This variable is the ~name expanded version of vendorlib, so that you
        may use it directly in Makefiles or shell scripts.

vendorman1dir (vendorman1dir.U):
        This variable contains the name of the directory for man1
        pages.  It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorman1direxp (vendorman1dir.U):
        This variable is the ~name expanded version of vendorman1dir, so that you
        may use it directly in Makefiles or shell scripts.

vendorman3dir (vendorman3dir.U):
        This variable contains the name of the directory for man3
        pages.  It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorman3direxp (vendorman3dir.U):
        This variable is the ~name expanded version of vendorman3dir, so that you
        may use it directly in Makefiles or shell scripts.

vendorprefix (vendorprefix.U):
        This variable holds the full absolute path of the directory below
        which the vendor will install add-on packages.
        See INSTALL for usage and examples.

vendorprefixexp (vendorprefix.U):
        This variable holds the full absolute path of the directory below
        which the vendor will install add-on packages.  Derived from vendorprefix.

vendorscript (vendorscript.U):
        This variable contains the eventual value of the VENDORSCRIPT symbol.
        It may have a ~ 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 Makefile.PL INSTALLDIRS=vendor
        or equivalent.  See INSTALL for details.

vendorscriptexp (vendorscript.U):
        This variable is the ~name expanded version of vendorscript, so that you
        may use it directly in Makefiles or shell scripts.

version (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.

version_patchlevel_string (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 myconfig.SH
        and lib/Config.pm.

versiononly (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 INSTALL for a more complete list).  Nor are the man
        pages installed.
        Usually, this is undef.

vi (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

xlibpth (libpth.U):
        This variable holds extra path (space-separated) used to find
        libraries on this platform, for example CPU-specific libraries
        (on multi-CPU platforms) may be listed here.

yacc (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.

yaccflags (yacc.U):
        This variable contains any additional yacc flags desired by the
        user.  It is up to the Makefile to use this.

zcat (Loc.U):
        This variable is defined but not used by Configure.
        The value is the empty string and is not useful.

zip (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 "zip" and is not useful.