Re: [PATCH] sv.c: consting

[p5sagit/p5-mst-13.2.git] / INSTALL

If you read this file _as_is_, just ignore the funny characters you see.
It is written in the POD format (see pod/perlpod.pod) which is specially
designed to be readable as is.

=head1 NAME

Install - Build and Installation guide for perl 5.

=head1 SYNOPSIS

First, make sure you have an up-to-date version of Perl.  If you
didn't get your Perl source from CPAN, check the latest version at
http://www.cpan.org/src/.  Perl uses a version scheme where even-numbered
subreleases (like 5.8.x and 5.10.x) are stable maintenance releases and
odd-numbered subreleases (like 5.7.x and 5.9.x) are unstable
development releases.  Development releases should not be used in
production environments.  Fixes and new features are first carefully
tested in development releases and only if they prove themselves to be
worthy will they be migrated to the maintenance releases.

The basic steps to build and install perl 5 on a Unix system with all
the defaults are to run, from a freshly unpacked source tree:

        sh Configure -de
        make
        make test
        make install

Each of these is explained in further detail below.

The above commands will install Perl to /usr/local (or some other
platform-specific directory -- see the appropriate file in hints/.)
If that's not okay with you, you can run Configure interactively, by
just typing "sh Configure" (without the -de args). You can also specify
any prefix location by adding "-Dprefix='/some/dir'" to Configure's args.
To explicitly name the perl binary, use the command
"make install PERLNAME=myperl".

These options, and many more, are explained in further detail below.

If you have problems, corrections, or questions, please see
L<"Reporting Problems"> below.

For information on what's new in this release, see the
pod/perl5110delta.pod file.  For more detailed information about specific
changes, see the Changes file.

=head1 DESCRIPTION

This document is written in pod format as an easy way to indicate its
structure.  The pod format is described in pod/perlpod.pod, but you can
read it as is with any pager or editor.  Headings and items are marked
by lines beginning with '='.  The other mark-up used is

    B<text>     embolden text, used for switches, programs or commands
    C<code>     literal code
    L<name>     A link (cross reference) to name
    F<file>     A filename

Although most of the defaults are probably fine for most users,
you should probably at least skim through this document before
proceeding.

In addition to this file, check if there is a README file specific to
your operating system, since it may provide additional or different
instructions for building Perl.  If there is a hint file for your
system (in the hints/ directory) you might also want to read it
for even more information.

For additional information about porting Perl, see the section on
L<"Porting information"> below, and look at the files in the Porting/
directory.

=head1 PRELIMINARIES

=head2 Changes and Incompatibilities

Please see pod/perl5110delta.pod for a description of the changes and
potential incompatibilities introduced with this release.  A few of
the most important issues are listed below, but you should refer
to pod/perl5110delta.pod for more detailed information.

B<WARNING:> This version is not binary compatible with prior releases of Perl.
If you have built extensions (i.e. modules that include C code)
using an earlier version of Perl, you will need to rebuild and reinstall
those extensions.

Pure perl modules without XS or C code should continue to work fine
without reinstallation.  See the discussion below on
L<"Coexistence with earlier versions of perl 5"> for more details.

The standard extensions supplied with Perl will be handled automatically.

On a related issue, old modules may possibly be affected by the changes
in the Perl language in the current release.  Please see
pod/perl5110delta.pod for a description of what's changed.  See your
installed copy of the perllocal.pod file for a (possibly incomplete)
list of locally installed modules.  Also see CPAN::autobundle for one
way to make a "bundle" of your currently installed modules.

=head1 Run Configure

Configure will figure out various things about your system.  Some
things Configure will figure out for itself, other things it will ask
you about.  To accept the default, just press RETURN.   The default is
almost always okay.  It is normal for some things to be "NOT found",
since Configure often searches for many different ways of performing
the same function.

At any Configure prompt, you can type  &-d  and Configure will use the
defaults from then on.

After it runs, Configure will perform variable substitution on all the
*.SH files and offer to run make depend.

The results of a Configure run are stored in the config.sh and Policy.sh
files.

=head2 Common Configure options

Configure supports a number of useful options.  Run

        Configure -h

to get a listing.  See the Porting/Glossary file for a complete list of
Configure variables you can set and their definitions.

=over 4

=item C compiler

To compile with gcc, if it's not the default compiler on your
system, you should run

        sh Configure -Dcc=gcc

This is the preferred way to specify gcc (or any another alternative
compiler) so that the hints files can set appropriate defaults.

=item Installation prefix

By default, for most systems, perl will be installed in
/usr/local/{bin, lib, man}.  (See L<"Installation Directories">
and L<"Coexistence with earlier versions of perl 5"> below for
further details.)

You can specify a different 'prefix' for the default installation
directory when Configure prompts you, or by using the Configure command
line option -Dprefix='/some/directory', e.g.

        sh Configure -Dprefix=/opt/perl

If your prefix contains the string "perl", then the suggested
directory structure is simplified.  For example, if you use
prefix=/opt/perl, then Configure will suggest /opt/perl/lib instead of
/opt/perl/lib/perl5/.  Again, see L<"Installation Directories"> below
for more details.  Do not include a trailing slash, (i.e. /opt/perl/)
or you may experience odd test failures.

NOTE:  You must not specify an installation directory that is the same
as or below your perl source directory.  If you do, installperl will
attempt infinite recursion.

=item /usr/bin/perl

It may seem obvious, but Perl is useful only when users can easily
find it.  It's often a good idea to have both /usr/bin/perl and
/usr/local/bin/perl be symlinks to the actual binary.  Be especially
careful, however, not to overwrite a version of perl supplied by your
vendor unless you are sure you know what you are doing.  If you insist
on replacing your vendor's perl, useful information on how it was
configured may be found with

        perl -V:config_args

(Check the output carefully, however, since this doesn't preserve
spaces in arguments to Configure.  For that, you have to look carefully
at config_arg1, config_arg2, etc.)

By default, Configure will not try to link /usr/bin/perl to the current
version of perl.  You can turn on that behavior by running

        Configure -Dinstallusrbinperl

or by answering 'yes' to the appropriate Configure prompt.

In any case, system administrators are strongly encouraged to put
(symlinks to) perl and its accompanying utilities, such as perldoc,
into a directory typically found along a user's PATH, or in another
obvious and convenient place.

=item Building a development release

For development releases (odd subreleases, like 5.9.x) if you want to
use Configure -d, you will also need to supply -Dusedevel to Configure,
because the default answer to the question "do you really want to
Configure a development version?" is "no".  The -Dusedevel skips that
sanity check.

=back

If you are willing to accept all the defaults, and you want terse
output, you can run

        sh Configure -des

=head2 Altering Configure variables for C compiler switches etc.

For most users, most of the Configure defaults are fine, or can easily
be set on the Configure command line.  However, if Configure doesn't
have an option to do what you want, you can change Configure variables
after the platform hints have been run by using Configure's -A switch.
For example, here's how to add a couple of extra flags to C compiler
invocations:

        sh Configure -Accflags="-DPERL_EXTERNAL_GLOB -DNO_HASH_SEED"

To clarify, those ccflags values are not Configure options; if passed to
Configure directly, they won't do anything useful (they will define a
variable in config.sh, but without taking any action based upon it).
But when passed to the compiler, those flags will activate #ifdefd code.

For more help on Configure switches, run

        sh Configure -h

=head2 Major Configure-time Build Options

There are several different ways to Configure and build perl for your
system.  For most users, the defaults are sensible and will work.
Some users, however, may wish to further customize perl.  Here are
some of the main things you can change.

=head3 Threads

On some platforms, perl can be compiled with support for threads.  To
enable this, run

        sh Configure -Dusethreads

The default is to compile without thread support.

Perl used to have two different internal threads implementations.  The current
model (available internally since 5.6, and as a user-level module since 5.8) is
called interpreter-based implementation (ithreads), with one interpreter per
thread, and explicit sharing of data.  The (deprecated) 5.005 version
(5005threads) has been removed for release 5.10.

The 'threads' module is for use with the ithreads implementation.  The
'Thread' module emulates the old 5005threads interface on top of the current
ithreads model.

When using threads, perl uses a dynamically-sized buffer for some of
the thread-safe library calls, such as those in the getpw*() family.
This buffer starts small, but it will keep growing until the result
fits.  To get a fixed upper limit, you should compile Perl with
PERL_REENTRANT_MAXSIZE defined to be the number of bytes you want.  One
way to do this is to run Configure with
C<-Accflags=-DPERL_REENTRANT_MAXSIZE=65536>.

=head3 Large file support

Since Perl 5.6.0, Perl has supported large files (files larger than
2 gigabytes), and in many common platforms like Linux or Solaris this
support is on by default.

This is both good and bad. It is good in that you can use large files,
seek(), stat(), and -s them.  It is bad in that if you are interfacing Perl
using some extension, the components you are connecting to must also
be large file aware: if Perl thinks files can be large but the other
parts of the software puzzle do not understand the concept, bad things
will happen.

There's also one known limitation with the current large files
implementation: unless you also have 64-bit integers (see the next
section), you cannot use the printf/sprintf non-decimal integer formats
like C<%x> to print filesizes.  You can use C<%d>, though.

If you want to compile perl without large file support, use

    sh Configure -Uuselargefiles

=head3 64 bit support

If your platform does not run natively at 64 bits, but can simulate
them with compiler flags and/or C<long long> or C<int64_t>,
you can build a perl that uses 64 bits.

There are actually two modes of 64-bitness: the first one is achieved
using Configure -Duse64bitint and the second one using Configure
-Duse64bitall.  The difference is that the first one is minimal and
the second one maximal.  The first works in more places than the second.

The C<use64bitint> option does only as much as is required to get
64-bit integers into Perl (this may mean, for example, using "long
longs") while your memory may still be limited to 2 gigabytes (because
your pointers could still be 32-bit).  Note that the name C<64bitint>
does not imply that your C compiler will be using 64-bit C<int>s (it
might, but it doesn't have to).  The C<use64bitint> simply means that
you will be able to have 64 bit-wide scalar values.

The C<use64bitall> option goes all the way by attempting to switch
integers (if it can), longs (and pointers) to being 64-bit.  This may
create an even more binary incompatible Perl than -Duse64bitint: the
resulting executable may not run at all in a 32-bit box, or you may
have to reboot/reconfigure/rebuild your operating system to be 64-bit
aware.

Natively 64-bit systems need neither -Duse64bitint nor -Duse64bitall.
On these systems, it might be the default compilation mode, and there
is currently no guarantee that passing no use64bitall option to the
Configure process will build a 32bit perl. Implementing -Duse32bit*
options is planned for perl 5.12.

=head3 Long doubles

In some systems you may be able to use long doubles to enhance the
range and precision of your double precision floating point numbers
(that is, Perl's numbers).  Use Configure -Duselongdouble to enable
this support (if it is available).

=head3 "more bits"

You can "Configure -Dusemorebits" to turn on both the 64-bit support
and the long double support.

=head3 Algorithmic Complexity Attacks on Hashes

In Perls 5.8.0 and earlier it was easy to create degenerate hashes.
Processing such hashes would consume large amounts of CPU time,
enabling a "Denial of Service" attack against Perl.  Such hashes may be
a problem for example for mod_perl sites, sites with Perl CGI scripts
and web services, that process data originating from external sources.

In Perl 5.8.1 a security feature was introduced to make it harder to
create such degenerate hashes. A visible side effect of this was that
the keys(), values(), and each() functions may return the hash elements
in different order between different runs of Perl even with the same
data.  It also had unintended binary incompatibility issues with
certain modules compiled against Perl 5.8.0.

In Perl 5.8.2 an improved scheme was introduced.  Hashes will return
elements in the same order as Perl 5.8.0 by default.  On a hash by hash
basis, if pathological data is detected during a hash key insertion,
then that hash will switch to an alternative random hash seed.  As
adding keys can always dramatically change returned hash element order,
existing programs will not be affected by this, unless they
specifically test for pre-recorded hash return order for contrived
data. (eg the list of keys generated by C<map {"\0"x$_} 0..15> trigger
randomisation) In effect the new implementation means that 5.8.1 scheme
is only being used on hashes which are under attack.

One can still revert to the old guaranteed repeatable order (and be
vulnerable to attack by wily crackers) by setting the environment
variable PERL_HASH_SEED, see L<perlrun/PERL_HASH_SEED>.  Another option
is to add -DUSE_HASH_SEED_EXPLICIT to the compilation flags (for
example by using C<Configure -Accflags=-DUSE_HASH_SEED_EXPLICIT>), in
which case one has to explicitly set the PERL_HASH_SEED environment
variable to enable the security feature, or by adding -DNO_HASH_SEED to
the compilation flags to completely disable the randomisation feature.

B<Perl has never guaranteed any ordering of the hash keys>, and the
ordering has already changed several times during the lifetime of Perl
5.  Also, the ordering of hash keys has always been, and continues to
be, affected by the insertion order.  Note that because of this
randomisation for example the Data::Dumper results will be different
between different runs of Perl, since Data::Dumper by default dumps
hashes "unordered".  The use of the Data::Dumper C<Sortkeys> option is
recommended.

=head3 SOCKS

Perl can be configured to be 'socksified', that is, to use the SOCKS
TCP/IP proxy protocol library.  SOCKS is used to give applications
access to transport layer network proxies.  Perl supports only SOCKS
Version 5.  The corresponding Configure option is -Dusesocks.
You can find more about SOCKS from wikipedia at
L<http://en.wikipedia.org/wiki/SOCKS>.

=head3 Dynamic Loading

By default, Configure will compile perl to use dynamic loading.
If you want to force perl to be compiled completely
statically, you can either choose this when Configure prompts you or
you can use the Configure command line option -Uusedl.
With this option, you won't be able to use any new extension
(XS) module without recompiling perl itself.

=head3 Building a shared Perl library

Currently, for most systems, the main perl executable is built by
linking the "perl library" libperl.a with perlmain.o, your static
extensions, and various extra libraries, such as -lm.

On systems that support dynamic loading, it may be possible to
replace libperl.a with a shared libperl.so.  If you anticipate building
several different perl binaries (e.g. by embedding libperl into
different programs, or by using the optional compiler extension), then
you might wish to build a shared libperl.so so that all your binaries
can share the same library.

The disadvantages are that there may be a significant performance
penalty associated with the shared libperl.so, and that the overall
mechanism is still rather fragile with respect to different versions
and upgrades.

In terms of performance, on my test system (Solaris 2.5_x86) the perl
test suite took roughly 15% longer to run with the shared libperl.so.
Your system and typical applications may well give quite different
results.

The default name for the shared library is typically something like
libperl.so.5.8.8 (for Perl 5.8.8), or libperl.so.588, or simply
libperl.so.  Configure tries to guess a sensible naming convention
based on your C library name.  Since the library gets installed in a
version-specific architecture-dependent directory, the exact name
isn't very important anyway, as long as your linker is happy.

You can elect to build a shared libperl by

        sh Configure -Duseshrplib

To build a shared libperl, the environment variable controlling shared
library search (LD_LIBRARY_PATH in most systems, DYLD_LIBRARY_PATH for
NeXTSTEP/OPENSTEP/Darwin, LIBRARY_PATH for BeOS, LD_LIBRARY_PATH/SHLIB_PATH
for HP-UX, LIBPATH for AIX, PATH for Cygwin) must be set up to include
the Perl build directory because that's where the shared libperl will
be created.  Configure arranges makefile to have the correct shared
library search settings.  You can find the name of the environment
variable Perl thinks works in your your system by

        grep ldlibpthname config.sh

However, there are some special cases where manually setting the
shared library path might be required.  For example, if you want to run
something like the following with the newly-built but not-yet-installed
./perl:

        cd t; ./perl -MTestInit misc/failing_test.t

or

        ./perl -Ilib ~/my_mission_critical_test

then you need to set up the shared library path explicitly.
You can do this with

   LD_LIBRARY_PATH=`pwd`:$LD_LIBRARY_PATH; export LD_LIBRARY_PATH

for Bourne-style shells, or

   setenv LD_LIBRARY_PATH `pwd`

for Csh-style shells.  (This procedure may also be needed if for some
unexpected reason Configure fails to set up makefile correctly.) (And
again, it may be something other than LD_LIBRARY_PATH for you, see above.)

You can often recognize failures to build/use a shared libperl from error
messages complaining about a missing libperl.so (or libperl.sl in HP-UX),
for example:

    18126:./miniperl: /sbin/loader: Fatal Error: cannot map libperl.so

There is also an potential problem with the shared perl library if you
want to have more than one "flavor" of the same version of perl (e.g.
with and without -DDEBUGGING).  For example, suppose you build and
install a standard Perl 5.10.0 with a shared library.  Then, suppose you
try to build Perl 5.10.0 with -DDEBUGGING enabled, but everything else
the same, including all the installation directories.  How can you
ensure that your newly built perl will link with your newly built
libperl.so.8 rather with the installed libperl.so.8?  The answer is
that you might not be able to.  The installation directory is encoded
in the perl binary with the LD_RUN_PATH environment variable (or
equivalent ld command-line option).  On Solaris, you can override that
with LD_LIBRARY_PATH; on Linux, you can only override at runtime via
LD_PRELOAD, specifying the exact filename you wish to be used; and on
Digital Unix, you can override LD_LIBRARY_PATH by setting the
_RLD_ROOT environment variable to point to the perl build directory.

In other words, it is generally not a good idea to try to build a perl
with a shared library if $archlib/CORE/$libperl already exists from a
previous build.

A good workaround is to specify a different directory for the
architecture-dependent library for your -DDEBUGGING version of perl.
You can do this by changing all the *archlib* variables in config.sh to
point to your new architecture-dependent library.

=head3 Environment access

Perl often needs to write to the program's environment, such as when C<%ENV>
is assigned to. Many implementations of the C library function C<putenv()>
leak memory, so where possible perl will manipulate the environment directly
to avoid these leaks. The default is now to perform direct manipulation
whenever perl is running as a stand alone interpreter, and to call the safe
but potentially leaky C<putenv()> function when the perl interpreter is
embedded in another application. You can force perl to always use C<putenv()>
by compiling with -DPERL_USE_SAFE_PUTENV. You can force an embedded perl to
use direct manipulation by setting C<PL_use_safe_putenv = 0;> after the
C<perl_construct()> call.

=head2 Installation Directories

The installation directories can all be changed by answering the
appropriate questions in Configure.  For convenience, all the installation
questions are near the beginning of Configure.  Do not include trailing
slashes on directory names.  At any point during the Configure process,
you can answer a question with  &-d  and Configure will use the defaults
from then on.  Alternatively, you can

        grep '^install' config.sh

after Configure has run to verify the installation paths.

The defaults are intended to be reasonable and sensible for most
people building from sources.  Those who build and distribute binary
distributions or who export perl to a range of systems will probably
need to alter them.  If you are content to just accept the defaults,
you can safely skip the next section.

The directories set up by Configure fall into three broad categories.

=over 4

=item Directories for the perl distribution

By default, Configure will use the following directories for 5.10.0.
$version is the full perl version number, including subversion, e.g.
5.10.0 or 5.9.5, and $archname is a string like sun4-sunos,
determined by Configure.  The full definitions of all Configure
variables are in the file Porting/Glossary.

    Configure variable  Default value
    $prefixexp          /usr/local
    $binexp             $prefixexp/bin
    $scriptdirexp       $prefixexp/bin
    $privlibexp         $prefixexp/lib/perl5/$version
    $archlibexp         $prefixexp/lib/perl5/$version/$archname
    $man1direxp         $prefixexp/man/man1
    $man3direxp         $prefixexp/man/man3
    $html1direxp        (none)
    $html3direxp        (none)

$prefixexp is generated from $prefix, with ~ expansion done to convert home
directories into absolute paths. Similarly for the other variables listed. As
file system calls do not do this, you should always reference the ...exp
variables, to support users who build perl in their home directory.

Actually, Configure recognizes the SVR3-style
/usr/local/man/l_man/man1 directories, if present, and uses those
instead.  Also, if $prefix contains the string "perl", the library
directories are simplified as described below.  For simplicity, only
the common style is shown here.

=item Directories for site-specific add-on files

After perl is installed, you may later wish to add modules (e.g. from
CPAN) or scripts.  Configure will set up the following directories to
be used for installing those add-on modules and scripts.

    Configure variable  Default value
    $siteprefixexp      $prefixexp
    $sitebinexp         $siteprefixexp/bin
    $sitescriptexp      $siteprefixexp/bin
    $sitelibexp         $siteprefixexp/lib/perl5/site_perl/$version
    $sitearchexp        $siteprefixexp/lib/perl5/site_perl/$version/$archname
    $siteman1direxp     $siteprefixexp/man/man1
    $siteman3direxp     $siteprefixexp/man/man3
    $sitehtml1direxp    (none)
    $sitehtml3direxp    (none)

By default, ExtUtils::MakeMaker will install architecture-independent
modules into $sitelib and architecture-dependent modules into $sitearch.

=item Directories for vendor-supplied add-on files

Lastly, if you are building a binary distribution of perl for
distribution, Configure can optionally set up the following directories
for you to use to distribute add-on modules.

    Configure variable  Default value
    $vendorprefixexp    (none)
    (The next ones are set only if vendorprefix is set.)
    $vendorbinexp       $vendorprefixexp/bin
    $vendorscriptexp    $vendorprefixexp/bin
    $vendorlibexp
        $vendorprefixexp/lib/perl5/vendor_perl/$version
    $vendorarchexp
        $vendorprefixexp/lib/perl5/vendor_perl/$version/$archname
    $vendorman1direxp   $vendorprefixexp/man/man1
    $vendorman3direxp   $vendorprefixexp/man/man3
    $vendorhtml1direxp  (none)
    $vendorhtml3direxp  (none)

These are normally empty, but may be set as needed.  For example,
a vendor might choose the following settings:

    $prefix             /usr
    $siteprefix         /usr/local
    $vendorprefix       /usr

This would have the effect of setting the following:

    $binexp             /usr/bin
    $scriptdirexp       /usr/bin
    $privlibexp         /usr/lib/perl5/$version
    $archlibexp         /usr/lib/perl5/$version/$archname
    $man1direxp         /usr/man/man1
    $man3direxp         /usr/man/man3

    $sitebinexp         /usr/local/bin
    $sitescriptexp      /usr/local/bin
    $sitelibexp         /usr/local/lib/perl5/site_perl/$version
    $sitearchexp        /usr/local/lib/perl5/site_perl/$version/$archname
    $siteman1direxp     /usr/local/man/man1
    $siteman3direxp     /usr/local/man/man3

    $vendorbinexp       /usr/bin
    $vendorscriptexp    /usr/bin
    $vendorlibexp       /usr/lib/perl5/vendor_perl/$version
    $vendorarchexp      /usr/lib/perl5/vendor_perl/$version/$archname
    $vendorman1direxp   /usr/man/man1
    $vendorman3direxp   /usr/man/man3

Note how in this example, the vendor-supplied directories are in the
/usr hierarchy, while the directories reserved for the end-user are in
the /usr/local hierarchy.

The entire installed library hierarchy is installed in locations with
version numbers, keeping the installations of different versions distinct.
However, later installations of Perl can still be configured to search the
installed libraries corresponding to compatible earlier versions.
See L<"Coexistence with earlier versions of perl 5"> below for more details
on how Perl can be made to search older version directories.

Of course you may use these directories however you see fit.  For
example, you may wish to use $siteprefix for site-specific files that
are stored locally on your own disk and use $vendorprefix for
site-specific files that are stored elsewhere on your organization's
network.  One way to do that would be something like

        sh Configure -Dsiteprefix=/usr/local -Dvendorprefix=/usr/share/perl

=item otherlibdirs

As a final catch-all, Configure also offers an $otherlibdirs
variable.  This variable contains a colon-separated list of additional
directories to add to @INC.  By default, it will be empty.
Perl will search these directories (including architecture and
version-specific subdirectories) for add-on modules and extensions.

For example, if you have a bundle of perl libraries from a previous
installation, perhaps in a strange place:

        Configure -Dotherlibdirs=/usr/lib/perl5/site_perl/5.8.1

=item APPLLIB_EXP

There is one other way of adding paths to @INC at perl build time, and
that is by setting the APPLLIB_EXP C pre-processor token to a colon-
separated list of directories, like this

       sh Configure -Accflags='-DAPPLLIB_EXP=\"/usr/libperl\"'

The directories defined by APPLLIB_EXP get added to @INC I<first>,
ahead of any others, and so provide a way to override the standard perl
modules should you, for example, want to distribute fixes without
touching the perl distribution proper.  And, like otherlib dirs,
version and architecture specific subdirectories are also searched, if
present, at run time.  Of course, you can still search other @INC
directories ahead of those in APPLLIB_EXP by using any of the standard
run-time methods: $PERLLIB, $PERL5LIB, -I, use lib, etc.

=item usesitecustomize

Run-time customization of @INC can be enabled with:

        sh Configure -Dusesitecustomize

which will define USE_SITECUSTOMIZE and $Config{usesitecustomize}.
When enabled, this makes perl run F<$sitelibexp/sitecustomize.pl> before
anything else.  This script can then be set up to add additional
entries to @INC.

=item Man Pages

By default, man pages will be installed in $man1dir and $man3dir, which
are normally /usr/local/man/man1 and /usr/local/man/man3.  If you
want to use a .3pm suffix for perl man pages, you can do that with

        sh Configure -Dman3ext=3pm

=item HTML pages

Currently, the standard perl installation does not do anything with
HTML documentation, but that may change in the future.  Further, some
add-on modules may wish to install HTML documents.  The html Configure
variables listed above are provided if you wish to specify where such
documents should be placed.  The default is "none", but will likely
eventually change to something useful based on user feedback.

=back

Some users prefer to append a "/share" to $privlib and $sitelib
to emphasize that those directories can be shared among different
architectures.

Note that these are just the defaults.  You can actually structure the
directories any way you like.  They don't even have to be on the same
filesystem.

Further details about the installation directories, maintenance and
development subversions, and about supporting multiple versions are
discussed in L<"Coexistence with earlier versions of perl 5"> below.

If you specify a prefix that contains the string "perl", then the
library directory structure is slightly simplified.  Instead of
suggesting $prefix/lib/perl5/, Configure will suggest $prefix/lib.

Thus, for example, if you Configure with
-Dprefix=/opt/perl, then the default library directories for 5.9.0 are

    Configure variable  Default value
        $privlib        /opt/perl/lib/5.9.0
        $archlib        /opt/perl/lib/5.9.0/$archname
        $sitelib        /opt/perl/lib/site_perl/5.9.0
        $sitearch       /opt/perl/lib/site_perl/5.9.0/$archname

=head2 Changing the installation directory

Configure distinguishes between the directory in which perl (and its
associated files) should be installed, and the directory in which it
will eventually reside.  For most sites, these two are the same; for
sites that use AFS, this distinction is handled automatically.
However, sites that use package management software such as rpm or
dpkg, or users building binary packages for distribution may also
wish to install perl into a different directory before moving perl
to its final destination.  There are two ways to do that:

=over 4

=item installprefix

To install perl under the /tmp/perl5 directory, use the following
command line:

    sh Configure -Dinstallprefix=/tmp/perl5

(replace /tmp/perl5 by a directory of your choice).

Beware, though, that if you go to try to install new add-on
modules, they too will get installed in under '/tmp/perl5' if you
follow this example.  That's why it's usually better to use DESTDIR,
as shown in the next section.

=item DESTDIR

If you need to install perl on many identical systems, it is convenient
to compile it once and create an archive that can be installed on
multiple systems.  Suppose, for example, that you want to create an
archive that can be installed in /opt/perl.  One way to do that is by
using the DESTDIR variable during C<make install>.  The DESTDIR is
automatically prepended to all the installation paths.  Thus you
simply do:

    sh Configure -Dprefix=/opt/perl -des
    make
    make test
    make install DESTDIR=/tmp/perl5
    cd /tmp/perl5/opt/perl
    tar cvf /tmp/perl5-archive.tar .

=back

=head2 Site-wide Policy settings

After Configure runs, it stores a number of common site-wide "policy"
answers (such as installation directories) in the Policy.sh file.
If you want to build perl on another system using the same policy
defaults, simply copy the Policy.sh file to the new system's perl build
directory, and Configure will use it. This will work even if Policy.sh was
generated for another version of Perl, or on a system with a
different architecture and/or operating system. However, in such cases,
you should review the contents of the file before using it: for
example, your new target may not keep its man pages in the same place
as the system on which the file was generated.

Alternatively, if you wish to change some or all of those policy
answers, you should

        rm -f Policy.sh

to ensure that Configure doesn't re-use them.

Further information is in the Policy_sh.SH file itself.

If the generated Policy.sh file is unsuitable, you may freely edit it
to contain any valid shell commands.  It will be run just after the
platform-specific hints files.

=head2 Disabling older versions of Perl

Configure will search for binary compatible versions of previously
installed perl binaries in the tree that is specified as target tree,
and these will be used as locations to search for modules by the perl
being built. The list of perl versions found will be put in the Configure
variable inc_version_list.

To disable this use of older perl modules, even completely valid pure perl
modules, you can specify to not include the paths found:

       sh Configure -Dinc_version_list=none ...

When using the newer perl, you can add these paths again in the
$PERL5LIB environment variable or with perl's -I runtime option.

=head2 Building Perl outside of the source directory

Sometimes it is desirable to build Perl in a directory different from
where the sources are, for example if you want to keep your sources
read-only, or if you want to share the sources between different binary
architectures.  You can do this (if your file system supports symbolic
links) by

        mkdir /tmp/perl/build/directory
        cd /tmp/perl/build/directory
        sh /path/to/perl/source/Configure -Dmksymlinks ...

This will create in /tmp/perl/build/directory a tree of symbolic links
pointing to files in /path/to/perl/source.  The original files are left
unaffected.  After Configure has finished you can just say

        make
        make test
        make install

as usual, and Perl will be built in /tmp/perl/build/directory.

=head2 Building a debugging perl

You can run perl scripts under the perl debugger at any time with
B<perl -d your_script>.  If, however, you want to debug perl itself,
you probably want to have support for perl internal debugging code
(activated by adding -DDEBUGGING to ccflags), and/or support for the
system debugger by adding -g to the optimisation flags. For that,
use the parameter:

        sh Configure -DDEBUGGING

or

        sh Configure -DDEBUGGING=<mode>

For a more eye appealing call, -DEBUGGING is defined to be an alias
for -DDEBUGGING. For both, the -U calls are also supported, in order
to be able to overrule the hints or Policy.sh settings.

Here are the DEBUGGING modes:

=over 4

=item -DDEBUGGING

=item -DEBUGGING

=item -DEBUGGING=both

Sets both -DDEBUGGING in the ccflags, and adds -g to optimize.

You can actually specify -g and -DDEBUGGING independently (see below),
but usually it's convenient to have both.

=item -DEBUGGING=-g

=item -Doptimize=-g

Adds -g to optimize, but does not set -DDEBUGGING.

(Note:  Your system may actually require something like cc -g2.
Check your man pages for cc(1) and also any hint file for your system.)

=item -DEBUGGING=none

=item -UDEBUGGING

Removes -g from optimize, and -DDEBUGGING from ccflags.

=back

If you are using a shared libperl, see the warnings about multiple
versions of perl under L<Building a shared Perl library>.

=head2 Extensions

Perl ships with a number of standard extensions.  These are contained
in the ext/ subdirectory.

By default, Configure will offer to build every extension which appears
to be supported.  For example, Configure will offer to build GDBM_File
only if it is able to find the gdbm library.

To disable certain extensions so that they are not built, use the
-Dnoextensions=... and -Donlyextensions=... options.  They both accept
a space-separated list of extensions.  The extensions listed in
C<noextensions> are removed from the list of extensions to build, while
the C<onlyextensions> is rather more severe and builds only the listed
extensions.  The latter should be used with extreme caution since
certain extensions are used by many other extensions and modules:
examples of such modules include Fcntl and IO.  The order of processing
these options is first C<only> (if present), then C<no> (if present).

Of course, you may always run Configure interactively and select only
the extensions you want.

If you unpack any additional extensions in the ext/ directory before
running Configure, then Configure will offer to build those additional
extensions as well.  Most users probably shouldn't have to do this --
it is usually easier to build additional extensions later after perl
has been installed.  However, if you wish to have those additional
extensions statically linked into the perl binary, then this offers a
convenient way to do that in one step.  (It is not necessary, however;
you can build and install extensions just fine even if you don't have
dynamic loading.  See lib/ExtUtils/MakeMaker.pm for more details.)
Another way of specifying extra modules is described in
L<"Adding extra modules to the build"> below.

If you re-use an old config.sh but change your system (e.g. by
adding libgdbm) Configure will still offer your old choices of extensions
for the default answer, but it will also point out the discrepancy to
you.

=head2 Including locally-installed libraries

Perl comes with interfaces to number of libraries, including threads,
dbm, ndbm, gdbm, and Berkeley db.  For the *db* extension, if
Configure can find the appropriate header files and libraries, it will
automatically include that extension.  The threading extension needs
to be specified explicitely (see L<Threads>).

Those libraries are not distributed with perl. If your header (.h) files
for those libraries are not in a directory normally searched by your C
compiler, then you will need to include the appropriate -I/your/directory
option when prompted by Configure.  If your libraries are not in a
directory normally searched by your C compiler and linker, then you will
need to include the appropriate -L/your/directory option when prompted
by Configure. See the examples below.

=head3 Examples

=over 4

=item gdbm in /usr/local

Suppose you have gdbm and want Configure to find it and build the
GDBM_File extension.  This example assumes you have gdbm.h
installed in /usr/local/include/gdbm.h and libgdbm.a installed in
/usr/local/lib/libgdbm.a.  Configure should figure all the
necessary steps out automatically.

Specifically, when Configure prompts you for flags for
your C compiler, you should include -I/usr/local/include, if it's
not here yet. Similarly, when Configure prompts you for linker flags,
you should include -L/usr/local/lib.

If you are using dynamic loading, then when Configure prompts you for
linker flags for dynamic loading, you should again include
-L/usr/local/lib.

Again, this should all happen automatically.  This should also work if
you have gdbm installed in any of (/usr/local, /opt/local, /usr/gnu,
/opt/gnu, /usr/GNU, or /opt/GNU).

=item gdbm in /usr/you

Suppose you have gdbm installed in some place other than /usr/local,
but you still want Configure to find it.  To be specific, assume you
have /usr/you/include/gdbm.h and /usr/you/lib/libgdbm.a.  You
still have to add -I/usr/you/include to cc flags, but you have to take
an extra step to help Configure find libgdbm.a.  Specifically, when
Configure prompts you for library directories, you have to add
/usr/you/lib to the list.

It is possible to specify this from the command line too (all on one
line):

    sh Configure -de \
        -Dlocincpth="/usr/you/include" \
        -Dloclibpth="/usr/you/lib"

locincpth is a space-separated list of include directories to search.
Configure will automatically add the appropriate -I directives.

loclibpth is a space-separated list of library directories to search.
Configure will automatically add the appropriate -L directives.  If
you have some libraries under /usr/local/ and others under
/usr/you, then you have to include both, namely

    sh Configure -de \
        -Dlocincpth="/usr/you/include /usr/local/include" \
        -Dloclibpth="/usr/you/lib /usr/local/lib"

=back

=head2 Overriding an old config.sh

If you want to use an old config.sh produced by a previous run of
Configure, but override some of the items with command line options, you
need to use B<Configure -O>.

=head2 GNU-style configure

If you prefer the GNU-style configure command line interface, you can
use the supplied configure.gnu command, e.g.

        CC=gcc ./configure.gnu

The configure.gnu script emulates a few of the more common configure
options.  Try

        ./configure.gnu --help

for a listing.

(The file is called configure.gnu to avoid problems on systems
that would not distinguish the files "Configure" and "configure".)

=head2 Malloc Issues

Perl relies heavily on malloc(3) to grow data structures as needed,
so perl's performance can be noticeably affected by the performance of
the malloc function on your system.  The perl source is shipped with a
version of malloc that has been optimized for the typical requests from
perl, so there's a chance that it may be both faster and use less memory
than your system malloc.

However, if your system already has an excellent malloc, or if you are
experiencing difficulties with extensions that use third-party libraries
that call malloc, then you should probably use your system's malloc.
(Or, you might wish to explore the malloc flags discussed below.)

=over 4

=item Using the system malloc

To build without perl's malloc, you can use the Configure command

        sh Configure -Uusemymalloc

or you can answer 'n' at the appropriate interactive Configure prompt.

Note that Perl's malloc isn't always used by default; that actually
depends on your system. For example, on Linux and FreeBSD (and many more
systems), Configure chooses to use the system's malloc by default.
See the appropriate file in the F<hints/> directory to see how the
default is set.

=item -DPERL_POLLUTE_MALLOC

NOTE: This flag is enabled automatically on some platforms if you just
run Configure to accept all the defaults.

Perl's malloc family of functions are normally called Perl_malloc(),
Perl_realloc(), Perl_calloc() and Perl_mfree().
These names do not clash with the system versions of these functions.

If this flag is enabled, however, Perl's malloc family of functions
will have the same names as the system versions.  This may be required
sometimes if you have libraries that like to free() data that may have
been allocated by Perl_malloc() and vice versa.

Note that enabling this option may sometimes lead to duplicate symbols
from the linker for malloc et al.  In such cases, the system probably
does not allow its malloc functions to be fully replaced with custom
versions.

=item -DPERL_DEBUGGING_MSTATS

This flag enables debugging mstats, which is required to use the
Devel::Peek::mstat() function. You cannot enable this unless you are
using Perl's malloc, so a typical Configure command would be

       sh Configure -Accflags=-DPERL_DEBUGGING_MSTATS -Dusemymalloc

to enable this option.

=back

=head2 What if it doesn't work?

If you run into problems, try some of the following ideas.
If none of them help, then see L<"Reporting Problems"> below.

=over 4

=item Running Configure Interactively

If Configure runs into trouble, remember that you can always run
Configure interactively so that you can check (and correct) its
guesses.

All the installation questions have been moved to the top, so you don't
have to wait for them.  Once you've handled them (and your C compiler and
flags) you can type  &-d  at the next Configure prompt and Configure
will use the defaults from then on.

If you find yourself trying obscure command line incantations and
config.over tricks, I recommend you run Configure interactively
instead.  You'll probably save yourself time in the long run.

=item Hint files

Hint files tell Configure about a number of things:

=over 4

=item o

The peculiarities or conventions of particular platforms -- non-standard
library locations and names, default installation locations for binaries,
and so on.

=item o

The deficiencies of the platform -- for example, library functions that,
although present, are too badly broken to be usable; or limits on
resources that are generously available on most platforms.

=item o

How best to optimize for the platform, both in terms of binary size and/or
speed, and for Perl feature support. Because of wide variations in the
implementation of shared libraries and of threading, for example, Configure
often needs hints in order to be able to use these features.

=back

The perl distribution includes many system-specific hints files
in the hints/ directory. If one of them matches your system, Configure
will offer to use that hint file. Unless you have a very good reason
not to, you should accept its offer.

Several of the hint files contain additional important information.
If you have any problems, it is a good idea to read the relevant hint file
for further information.  See hints/solaris_2.sh for an extensive example.
More information about writing good hints is in the hints/README.hints
file, which also explains hint files known as callback-units.

Note that any hint file is read before any Policy file, meaning that
Policy overrides hints -- see L</Site-wide Policy settings>.

=item WHOA THERE!!!

If you are re-using an old config.sh, it's possible that Configure detects
different values from the ones specified in this file.  You will almost
always want to keep the previous value, unless you have changed something
on your system.

For example, suppose you have added libgdbm.a to your system
and you decide to reconfigure perl to use GDBM_File.  When you run
Configure again, you will need to add -lgdbm to the list of libraries.
Now, Configure will find your gdbm include file and library and will
issue a message:

    *** WHOA THERE!!! ***
        The previous value for $i_gdbm on this machine was "undef"!
        Keep the previous value? [y]

In this case, you do not want to keep the previous value, so you
should answer 'n'.  (You'll also have to manually add GDBM_File to
the list of dynamic extensions to build.)

=item Changing Compilers

If you change compilers or make other significant changes, you should
probably not re-use your old config.sh.  Simply remove it or
rename it, then rerun Configure with the options you want to use.

=item Propagating your changes to config.sh

If you make any changes to config.sh, you should propagate
them to all the .SH files by running

        sh Configure -S

You will then have to rebuild by running

        make depend
        make

=item config.over and config.arch

You can also supply a shell script config.over to over-ride
Configure's guesses.  It will get loaded up at the very end, just
before config.sh is created.  You have to be careful with this,
however, as Configure does no checking that your changes make sense.
This file is usually good for site-specific customizations.

There is also another file that, if it exists, is loaded before the
config.over, called config.arch.  This file is intended to be per
architecture, not per site, and usually it's the architecture-specific
hints file that creates the config.arch.

=item config.h

Many of the system dependencies are contained in config.h.
Configure builds config.h by running the config_h.SH script.
The values for the variables are taken from config.sh.

If there are any problems, you can edit config.h directly.  Beware,
though, that the next time you run Configure, your changes will be
lost.

=item cflags

If you have any additional changes to make to the C compiler command
line, they can be made in cflags.SH.  For instance, to turn off the
optimizer on toke.c, find the line in the switch structure for
toke.c and put the command optimize='-g' before the ;; .  You
can also edit cflags directly, but beware that your changes will be
lost the next time you run Configure.

To explore various ways of changing ccflags from within a hint file,
see the file hints/README.hints.

To change the C flags for all the files, edit config.sh and change either
$ccflags or $optimize, and then re-run

        sh Configure -S
        make depend

=item No sh

If you don't have sh, you'll have to copy the sample file
Porting/config.sh to config.sh and edit your config.sh to reflect your
system's peculiarities.  See Porting/pumpkin.pod for more information.
You'll probably also have to extensively modify the extension building
mechanism.

=item Porting information

Specific information for the OS/2, Plan 9, VMS and Win32 ports is in the
corresponding README files and subdirectories.  Additional information,
including a glossary of all those config.sh variables, is in the Porting
subdirectory.  Porting/Glossary should especially come in handy.

Ports for other systems may also be available.  You should check out
http://www.cpan.org/ports for current information on ports to
various other operating systems.

If you plan to port Perl to a new architecture, study carefully the
section titled "Philosophical Issues in Patching and Porting Perl"
in the file Porting/pumpkin.pod and the file Porting/patching.pod.
Study also how other non-UNIX ports have solved problems.

=back

=head2 Adding extra modules to the build

You can specify extra modules or module bundles to be fetched from the
CPAN and installed as part of the Perl build.  Either use the -Dextras=...
command line parameter to Configure, for example like this:

        Configure -Dextras="Bundle::LWP DBI"

or answer first 'y' to the question 'Install any extra modules?' and
then answer "Bundle::LWP DBI" to the 'Extras?' question.
The module or the bundle names are as for the CPAN module 'install' command.
This will only work if those modules are to be built as dynamic
extensions.  If you wish to include those extra modules as static
extensions, see L<"Extensions"> above.

Notice that because the CPAN module will be used to fetch the extra
modules, you will need access to the CPAN, either via the Internet,
or via a local copy such as a CD-ROM or a local CPAN mirror.  If you
do not, using the extra modules option will die horribly.

Also notice that you yourself are responsible for satisfying any extra
dependencies such as external headers or libraries BEFORE trying the build.
For example: you will need to have the Foo database specific
headers and libraries installed for the DBD::Foo module.  The Configure
process or the Perl build process will not help you with these.

=head2 suidperl

suidperl is an optional component, which is normally neither built
nor installed by default.  From perlfaq1:

        On some systems, setuid and setgid scripts (scripts written
        in the C shell, Bourne shell, or Perl, for example, with the
        set user or group ID permissions enabled) are insecure due to
        a race condition in the kernel. For those systems, Perl versions
        5 and 4 attempt to work around this vulnerability with an optional
        component, a special program named suidperl, also known as sperl.
        This program attempts to emulate the set-user-ID and set-group-ID
        features of the kernel.

Because of the buggy history of suidperl, and the difficulty
of properly security auditing as large and complex piece of
software as Perl, we cannot recommend using suidperl and the feature
should be considered deprecated.

Instead, use a tool specifically designed to handle changes in
privileges, such as B<sudo>.

=head1 make depend

This will look for all the includes.  The output is stored in makefile.
The only difference between Makefile and makefile is the dependencies at
the bottom of makefile.  If you have to make any changes, you should edit
makefile, not Makefile, since the Unix make command reads makefile first.
(On non-Unix systems, the output may be stored in a different file.
Check the value of $firstmakefile in your config.sh if in doubt.)

Configure will offer to do this step for you, so it isn't listed
explicitly above.

=head1 make

This will attempt to make perl in the current directory.

=head2 Expected errors

These error reports are normal, and can be ignored:

  ...
  make: [extra.pods] Error 1 (ignored)
  ...
  make: [extras.make] Error 1 (ignored)

=head2 What if it doesn't work?

If you can't compile successfully, try some of the following ideas.
If none of them help, and careful reading of the error message and
the relevant manual pages on your system doesn't help,
then see L<"Reporting Problems"> below.

=over 4

=item hints

If you used a hint file, try reading the comments in the hint file
for further tips and information.

=item extensions

If you can successfully build miniperl, but the process crashes
during the building of extensions, run

        make minitest

to test your version of miniperl.

=item locale

If you have any locale-related environment variables set, try unsetting
them.  I have some reports that some versions of IRIX hang while
running B<./miniperl configpm> with locales other than the C locale.
See the discussion under L<"make test"> below about locales and the
whole L<perllocale/"LOCALE PROBLEMS"> section in the file pod/perllocale.pod.
The latter is especially useful if you see something like this

        perl: warning: Setting locale failed.
        perl: warning: Please check that your locale settings:
                LC_ALL = "En_US",
                LANG = (unset)
            are supported and installed on your system.
        perl: warning: Falling back to the standard locale ("C").

at Perl startup.

=item varargs

If you get varargs problems with gcc, be sure that gcc is installed
correctly and that you are not passing -I/usr/include to gcc.  When using
gcc, you should probably have i_stdarg='define' and i_varargs='undef'
in config.sh.  The problem is usually solved by installing gcc
correctly.  If you do change config.sh, don't forget to propagate
your changes (see L<"Propagating your changes to config.sh"> below).
See also the L<"vsprintf"> item below.

=item util.c

If you get error messages such as the following (the exact line
numbers and function name may vary in different versions of perl):

    util.c: In function `Perl_form':
    util.c:1107: number of arguments doesn't match prototype
    proto.h:125: prototype declaration

it might well be a symptom of the gcc "varargs problem".  See the
previous L<"varargs"> item.

=item LD_LIBRARY_PATH

If you run into dynamic loading problems, check your setting of
the LD_LIBRARY_PATH environment variable.  If you're creating a static
Perl library (libperl.a rather than libperl.so) it should build
fine with LD_LIBRARY_PATH unset, though that may depend on details
of your local set-up.

=item nm extraction

If Configure seems to be having trouble finding library functions,
try not using nm extraction.  You can do this from the command line
with

        sh Configure -Uusenm

or by answering the nm extraction question interactively.
If you have previously run Configure, you should not reuse your old
config.sh.

=item umask not found

If the build processes encounters errors relating to umask(), the problem
is probably that Configure couldn't find your umask() system call.
Check your config.sh.  You should have d_umask='define'.  If you don't,
this is probably the L<"nm extraction"> problem discussed above.  Also,
try reading the hints file for your system for further information.

=item vsprintf

If you run into problems with vsprintf in compiling util.c, the
problem is probably that Configure failed to detect your system's
version of vsprintf().  Check whether your system has vprintf().
(Virtually all modern Unix systems do.)  Then, check the variable
d_vprintf in config.sh.  If your system has vprintf, it should be:

        d_vprintf='define'

If Configure guessed wrong, it is likely that Configure guessed wrong
on a number of other common functions too.  This is probably
the L<"nm extraction"> problem discussed above.

=item do_aspawn

If you run into problems relating to do_aspawn or do_spawn, the
problem is probably that Configure failed to detect your system's
fork() function.  Follow the procedure in the previous item
on L<"nm extraction">.

=item __inet_* errors

If you receive unresolved symbol errors during Perl build and/or test
referring to __inet_* symbols, check to see whether BIND 8.1 is
installed.  It installs a /usr/local/include/arpa/inet.h that refers to
these symbols.  Versions of BIND later than 8.1 do not install inet.h
in that location and avoid the errors.  You should probably update to a
newer version of BIND (and remove the files the old one left behind).
If you can't, you can either link with the updated resolver library provided
with BIND 8.1 or rename /usr/local/bin/arpa/inet.h during the Perl build and
test process to avoid the problem.

=item .*_r() prototype NOT found

On a related note, if you see a bunch of complaints like the above about
reentrant functions - specifically networking-related ones - being present
but without prototypes available, check to see if BIND 8.1 (or possibly
other BIND 8 versions) is (or has been) installed. They install
header files such as netdb.h into places such as /usr/local/include (or into
another directory as specified at build/install time), at least optionally.
Remove them or put them in someplace that isn't in the C preprocessor's
header file include search path (determined by -I options plus defaults,
normally /usr/include).

=item #error "No DATAMODEL_NATIVE specified"

This is a common error when trying to build perl on Solaris 2.6 with a
gcc installation from Solaris 2.5 or 2.5.1.  The Solaris header files
changed, so you need to update your gcc installation.  You can either
rerun the fixincludes script from gcc or take the opportunity to
update your gcc installation.

=item Optimizer

If you can't compile successfully, try turning off your compiler's
optimizer.  Edit config.sh and change the line

        optimize='-O'

to

        optimize=' '

then propagate your changes with B<sh Configure -S> and rebuild
with B<make depend; make>.

=item Missing functions and Undefined symbols

If the build of miniperl fails with a long list of missing functions or
undefined symbols, check the libs variable in the config.sh file.  It
should look something like

        libs='-lsocket -lnsl -ldl -lm -lc'

The exact libraries will vary from system to system, but you typically
need to include at least the math library -lm.  Normally, Configure
will suggest the correct defaults.  If the libs variable is empty, you
need to start all over again.  Run

        make distclean

and start from the very beginning.  This time, unless you are sure of
what you are doing, accept the default list of libraries suggested by
Configure.

If the libs variable looks correct, you might have the
L<"nm extraction"> problem discussed above.

If you stil have missing routines or undefined symbols, you probably
need to add some library or other, or you need to undefine some feature
that Configure thought was there but is defective or incomplete.  If
you used a hint file, see if it has any relevant advice.  You can also
look through through config.h for likely suspects.

=item toke.c

Some compilers will not compile or optimize the larger files (such as
toke.c) without some extra switches to use larger jump offsets or
allocate larger internal tables.  You can customize the switches for
each file in cflags.  It's okay to insert rules for specific files into
makefile since a default rule only takes effect in the absence of a
specific rule.

=item Missing dbmclose

SCO prior to 3.2.4 may be missing dbmclose().  An upgrade to 3.2.4
that includes libdbm.nfs (which includes dbmclose()) may be available.

=item Note (probably harmless): No library found for -lsomething

If you see such a message during the building of an extension, but
the extension passes its tests anyway (see L<"make test"> below),
then don't worry about the warning message.  The extension
Makefile.PL goes looking for various libraries needed on various
systems; few systems will need all the possible libraries listed.
For example, a system may have -lcposix or -lposix, but it's
unlikely to have both, so most users will see warnings for the one
they don't have.  The phrase 'probably harmless' is intended to
reassure you that nothing unusual is happening, and the build
process is continuing.

On the other hand, if you are building GDBM_File and you get the
message

    Note (probably harmless): No library found for -lgdbm

then it's likely you're going to run into trouble somewhere along
the line, since it's hard to see how you can use the GDBM_File
extension without the -lgdbm library.

It is true that, in principle, Configure could have figured all of
this out, but Configure and the extension building process are not
quite that tightly coordinated.

=item sh: ar: not found

This is a message from your shell telling you that the command 'ar'
was not found.  You need to check your PATH environment variable to
make sure that it includes the directory with the 'ar' command.  This
is a common problem on Solaris, where 'ar' is in the /usr/ccs/bin
directory.

=item db-recno failure on tests 51, 53 and 55

Old versions of the DB library (including the DB library which comes
with FreeBSD 2.1) had broken handling of recno databases with modified
bval settings.  Upgrade your DB library or OS.

=item Bad arg length for semctl, is XX, should be ZZZ

If you get this error message from the ext/IPC/SysV/t/sem test, your System
V IPC may be broken.  The XX typically is 20, and that is what ZZZ
also should be.  Consider upgrading your OS, or reconfiguring your OS
to include the System V semaphores.

=item ext/IPC/SysV/t/sem........semget: No space left on device

Either your account or the whole system has run out of semaphores.  Or
both.  Either list the semaphores with "ipcs" and remove the unneeded
ones (which ones these are depends on your system and applications)
with "ipcrm -s SEMAPHORE_ID_HERE" or configure more semaphores to your
system.

=item GNU binutils

If you mix GNU binutils (nm, ld, ar) with equivalent vendor-supplied
tools you may be in for some trouble.  For example creating archives
with an old GNU 'ar' and then using a new current vendor-supplied 'ld'
may lead into linking problems.  Either recompile your GNU binutils
under your current operating system release, or modify your PATH not
to include the GNU utils before running Configure, or specify the
vendor-supplied utilities explicitly to Configure, for example by
Configure -Dar=/bin/ar.

=item THIS PACKAGE SEEMS TO BE INCOMPLETE

The F<Configure> program has not been able to find all the files which
make up the complete Perl distribution.  You may have a damaged source
archive file (in which case you may also have seen messages such as
C<gzip: stdin: unexpected end of file> and C<tar: Unexpected EOF on
archive file>), or you may have obtained a structurally-sound but
incomplete archive.  In either case, try downloading again from the
official site named at the start of this document.  If you do find
that any site is carrying a corrupted or incomplete source code
archive, please report it to the site's maintainer.

=item invalid token: ##

You are using a non-ANSI-compliant C compiler.  To compile Perl, you
need to use a compiler that supports ANSI C.  If there is a README
file for your system, it may have further details on your compiler
options.

=item Miscellaneous

Some additional things that have been reported:

Genix may need to use libc rather than libc_s, or #undef VARARGS.

NCR Tower 32 (OS 2.01.01) may need -W2,-Sl,2000 and #undef MKDIR.

UTS may need one or more of -K or -g, and undef LSTAT.

FreeBSD can fail the ext/IPC/SysV/t/sem.t test if SysV IPC has not been
configured in the kernel.  Perl tries to detect this, though, and
you will get a message telling you what to do.

Building Perl on a system that has also BIND (headers and libraries)
installed may run into troubles because BIND installs its own netdb.h
and socket.h, which may not agree with the operating system's ideas of
the same files.  Similarly, including -lbind may conflict with libc's
view of the world.  You may have to tweak -Dlocincpth and -Dloclibpth
to avoid the BIND.

=back

=head2 Cross-compilation

Perl can be cross-compiled.  It is just not trivial, cross-compilation
rarely is.  Perl is routinely cross-compiled for many platforms (as of
June 2005 at least PocketPC aka WinCE, Open Zaurus, EPOC, Symbian, and
the IBM OS/400).  These platforms are known as the B<target> platforms,
while the systems where the compilation takes place are the B<host>
platforms.

What makes the situation difficult is that first of all,
cross-compilation environments vary significantly in how they are set
up and used, and secondly because the primary way of configuring Perl
(using the rather large Unix-tool-dependent Configure script) is not
awfully well suited for cross-compilation.  However, starting from
version 5.8.0, the Configure script also knows one way of supporting
cross-compilation support, please keep reading.

See the following files for more information about compiling Perl for
the particular platforms:

=over 4

=item WinCE/PocketPC

README.ce

=item Open Zaurus

Cross/README

=item EPOC

README.epoc

=item Symbian

README.symbian

=item OS/400

README.os400

=back

Packaging and transferring either the core Perl modules or CPAN
modules to the target platform is also left up to the each
cross-compilation environment.  Often the cross-compilation target
platforms are somewhat limited in diskspace: see the section
L<Minimizing the Perl installation> to learn more of the minimal set
of files required for a functional Perl installation.

For some cross-compilation environments the Configure option
C<-Dinstallprefix=...> might be handy, see L<Changing the installation
directory>.

About the cross-compilation support of Configure: what is known to
work is running Configure in a cross-compilation environment and
building the miniperl executable.  What is known not to work is
building the perl executable because that would require building
extensions: Dynaloader statically and File::Glob dynamically, for
extensions one needs MakeMaker and MakeMaker is not yet
cross-compilation aware, and neither is the main Makefile.

The cross-compilation setup of Configure has successfully been used in
at least two Linux cross-compilation environments.  The setups were
both such that the host system was Intel Linux with a gcc built for
cross-compiling into ARM Linux, and there was a SSH connection to the
target system.

To run Configure in cross-compilation mode the basic switch that
has to be used is C<-Dusecrosscompile>.

   sh ./Configure -des -Dusecrosscompile -D...

This will make the cpp symbol USE_CROSS_COMPILE and the %Config
symbol C<usecrosscompile> available, and C<xconfig.h> will be used
for cross-compilation.

During the Configure and build, certain helper scripts will be created
into the Cross/ subdirectory.  The scripts are used to execute a
cross-compiled executable, and to transfer files to and from the
target host.  The execution scripts are named F<run-*> and the
transfer scripts F<to-*> and F<from-*>.  The part after the dash is
the method to use for remote execution and transfer: by default the
methods are B<ssh> and B<scp>, thus making the scripts F<run-ssh>,
F<to-scp>, and F<from-scp>.

To configure the scripts for a target host and a directory (in which
the execution will happen and which is to and from where the transfer
happens), supply Configure with

    -Dtargethost=so.me.ho.st -Dtargetdir=/tar/get/dir

The targethost is what e.g. ssh will use as the hostname, the targetdir
must exist (the scripts won't create it), the targetdir defaults to /tmp.
You can also specify a username to use for ssh/rsh logins

    -Dtargetuser=luser

but in case you don't, "root" will be used.

Because this is a cross-compilation effort, you will also need to specify
which target environment and which compilation environment to use.
This includes the compiler, the header files, and the libraries.
In the below we use the usual settings for the iPAQ cross-compilation
environment:

    -Dtargetarch=arm-linux
    -Dcc=arm-linux-gcc
    -Dusrinc=/skiff/local/arm-linux/include
    -Dincpth=/skiff/local/arm-linux/include
    -Dlibpth=/skiff/local/arm-linux/lib

If the name of the C<cc> has the usual GNU C semantics for cross
compilers, that is, CPU-OS-gcc, the names of the C<ar>, C<nm>, and
C<ranlib> will also be automatically chosen to be CPU-OS-ar and so on.
(The C<ld> requires more thought and will be chosen later by Configure
as appropriate.)  Also, in this case the incpth, libpth, and usrinc
will be guessed by Configure (unless explicitly set to something else,
in which case Configure's guesses with be appended).

In addition to the default execution/transfer methods you can also
choose B<rsh> for execution, and B<rcp> or B<cp> for transfer,
for example:

    -Dtargetrun=rsh -Dtargetto=rcp -Dtargetfrom=cp

Putting it all together:

    sh ./Configure -des -Dusecrosscompile \
        -Dtargethost=so.me.ho.st \
        -Dtargetdir=/tar/get/dir \
        -Dtargetuser=root \
        -Dtargetarch=arm-linux \
        -Dcc=arm-linux-gcc \
        -Dusrinc=/skiff/local/arm-linux/include \
        -Dincpth=/skiff/local/arm-linux/include \
        -Dlibpth=/skiff/local/arm-linux/lib \
        -D...

or if you are happy with the defaults:

    sh ./Configure -des -Dusecrosscompile \
        -Dtargethost=so.me.ho.st \
        -Dcc=arm-linux-gcc \
        -D...

Another example where the cross-compiler has been installed under
F</usr/local/arm/2.95.5>:

    sh ./Configure -des -Dusecrosscompile \
        -Dtargethost=so.me.ho.st \
        -Dcc=/usr/local/arm/2.95.5/bin/arm-linux-gcc \
        -Dincpth=/usr/local/arm/2.95.5/include \
        -Dusrinc=/usr/local/arm/2.95.5/include \
        -Dlibpth=/usr/local/arm/2.95.5/lib

=head1 make test

This will run the regression tests on the perl you just made.  If
'make test' doesn't say "All tests successful" then something went
wrong.  See the file t/README in the t subdirectory.

Note that you can't run the tests in background if this disables
opening of /dev/tty. You can use 'make test-notty' in that case but
a few tty tests will be skipped.

=head2 What if make test doesn't work?

If make test bombs out, just cd to the t directory and run ./TEST
by hand to see if it makes any difference.  If individual tests
bomb, you can run them by hand, e.g.,

        cd t ; ./perl -MTestInit op/groups.t

Another way to get more detailed information about failed tests and
individual subtests is to cd to the t directory and run

        cd t ; ./perl harness <list of tests>

(this assumes that most basic tests succeed, since harness uses
complicated constructs). If no list of tests is provided, harness
will run all tests.

You should also read the individual tests to see if there are any helpful
comments that apply to your system.  You may also need to setup your
shared library path if you get errors like:

        /sbin/loader: Fatal Error: cannot map libperl.so

See L</"Building a shared Perl library"> earlier in this document.

=over 4

=item locale

Note:  One possible reason for errors is that some external programs
may be broken due to the combination of your environment and the way
'make test' exercises them.  For example, this may happen if you have
one or more of these environment variables set:  LC_ALL LC_CTYPE
LC_COLLATE LANG.  In some versions of UNIX, the non-English locales
are known to cause programs to exhibit mysterious errors.

If you have any of the above environment variables set, please try

        setenv LC_ALL C

(for C shell) or

        LC_ALL=C;export LC_ALL

for Bourne or Korn shell) from the command line and then retry
make test.  If the tests then succeed, you may have a broken program that
is confusing the testing.  Please run the troublesome test by hand as
shown above and see whether you can locate the program.  Look for
things like:  exec, `backquoted command`, system, open("|...") or
open("...|").  All these mean that Perl is trying to run some
external program.

=item Timing problems

Several tests in the test suite check timing functions, such as
sleep(), and see if they return in a reasonable amount of time.
If your system is quite busy and doesn't respond quickly enough,
these tests might fail.  If possible, try running the tests again
with the system under a lighter load.  These timing-sensitive
and load-sensitive tests include F<t/op/alarm.t>,
F<ext/Time/HiRes/t/HiRes.t>, F<ext/threads/shared/t/waithires.t>,
F<ext/threads/shared/t/stress.t>, F<lib/Benchmark.t>,
F<lib/Memoize/t/expmod_t.t>, and F<lib/Memoize/t/speed.t>.

You might also experience some failures in F<t/op/stat.t> if you build
perl on an NFS filesystem, if the remote clock and the system clock are
different.

=item Out of memory

On some systems, particularly those with smaller amounts of RAM, some
of the tests in t/op/pat.t may fail with an "Out of memory" message.
For example, on my SparcStation IPC with 12 MB of RAM, in perl5.5.670,
test 85 will fail if run under either t/TEST or t/harness.

Try stopping other jobs on the system and then running the test by itself:

        cd t; ./perl -MTestInit op/pat.t

to see if you have any better luck.  If your perl still fails this
test, it does not necessarily mean you have a broken perl.  This test
tries to exercise the regular expression subsystem quite thoroughly,
and may well be far more demanding than your normal usage.

=item Failures from lib/File/Temp/t/security saying "system possibly insecure"

First, such warnings are not necessarily serious or indicative of a
real security threat.  That being said, they bear investigating.

Note that each of the tests is run twice.  The first time is in the
directory returned by File::Spec->tmpdir() (often /tmp on Unix
systems), and the second time in the directory from which the test was
run (usually the 't' directory, if the test was run as part of 'make
test').

The tests may fail for the following reasons:

(1) If the directory the tests are being run in is owned by somebody
other than the user running the tests, or by root (uid 0).

This failure can happen if the Perl source code distribution is
unpacked in such a way that the user ids in the distribution package
are used as-is.  Some tar programs do this.

(2) If the directory the tests are being run in is writable by group or
by others, and there is no sticky bit set for the directory.  (With
UNIX/POSIX semantics, write access to a directory means the right to
add or remove files in that directory.  The 'sticky bit' is a feature
used in some UNIXes to give extra protection to files: if the bit is
set for a directory, no one but the owner (or root) can remove that
file even if the permissions would otherwise allow file removal by
others.)

This failure may or may not be a real problem: it depends on the
permissions policy used on this particular system.  This failure can
also happen if the system either doesn't support the sticky bit (this
is the case with many non-UNIX platforms: in principle File::Temp
should know about these platforms and skip the tests), or if the system
supports the sticky bit but for some reason or reasons it is not being
used.  This is, for example, the case with HP-UX: as of HP-UX release
11.00, the sticky bit is very much supported, but HP-UX doesn't use it
on its /tmp directory as shipped.  Also, as with the permissions, some
local policy might dictate that the stickiness is not used.

(3) If the system supports the POSIX 'chown giveaway' feature and if
any of the parent directories of the temporary file back to the root
directory are 'unsafe', using the definitions given above in (1) and
(2).  For Unix systems, this is usually not an issue if you are
building on a local disk.  See the documentation for the File::Temp
module for more information about 'chown giveaway'.

See the documentation for the File::Temp module for more information
about the various security aspects of temporary files.

=back

=head1 make install

This will put perl into the public directory you specified to
Configure; by default this is /usr/local/bin.  It will also try
to put the man pages in a reasonable place.  It will not nroff the man
pages, however.  You may need to be root to run B<make install>.  If you
are not root, you must still have permission to install into the directories
in question and you should ignore any messages about chown not working.

If "make install" just says "`install' is up to date" or something
similar, you may be on a case-insensitive filesystems such as Mac's HFS+,
and you should say "make install-all".  (This confusion is brought to you
by the Perl distribution having a file called INSTALL.)

=head2 Installing perl under different names

If you want to install perl under a name other than "perl" (for example,
when installing perl with special features enabled, such as debugging),
indicate the alternate name on the "make install" line, such as:

    make install PERLNAME=myperl

You can separately change the base used for versioned names (like
"perl5.8.9") by setting PERLNAME_VERBASE, like

    make install PERLNAME=perl5 PERLNAME_VERBASE=perl

This can be useful if you have to install perl as "perl5" (e.g. to
avoid conflicts with an ancient version in /usr/bin supplied by your vendor).
Without this the versioned binary would be called "perl55.8.8".

=head2 Installing perl under a different directory

You can install perl under a different destination directory by using
the DESTDIR variable during C<make install>, with a command like

        make install DESTDIR=/tmp/perl5

DESTDIR is automatically prepended to all the installation paths.  See
the example in L<"DESTDIR"> above.

=head2 Installed files

If you want to see exactly what will happen without installing
anything, you can run

        ./perl installperl -n
        ./perl installman -n

make install will install the following:

    binaries

        perl,
            perl5.n.n   where 5.n.n is the current release number.  This
                        will be a link to perl.
        suidperl,
            sperl5.n.n  If you requested setuid emulation.
        a2p             awk-to-perl translator

    scripts

        cppstdin        This is used by the deprecated switch perl -P, if
                        your cc -E can't read from stdin.
        c2ph, pstruct   Scripts for handling C structures in header files.
        config_data     Manage Module::Build-like module configuration
        corelist        Shows versions of modules that come with different
                        versions of perl
        cpan            The CPAN shell
        cpan2dist       The CPANPLUS distribution creator
        cpanp           The CPANPLUS shell
        cpanp-run-perl  An helper for cpanp
        dprofpp         Perl code profiler post-processor
        enc2xs          Encoding module generator
        find2perl       find-to-perl translator
        h2ph            Extract constants and simple macros from C headers
        h2xs            Converts C .h header files to Perl extensions.
        instmodsh       A shell to examine installed modules.
        libnetcfg       Configure libnet.
        perlbug         Tool to report bugs in Perl.
        perldoc         Tool to read perl's pod documentation.
        perlivp         Perl Installation Verification Procedure
        piconv          A Perl implementation of the encoding conversion
                        utility iconv
        pl2pm           Convert Perl 4 .pl files to Perl 5 .pm modules
        pod2html,       Converters from perl's pod documentation format
        pod2latex,      to other useful formats.
        pod2man,
        pod2text,
        pod2usage
        podchecker      POD syntax checker
        podselect       Prints sections of POD documentation
        prove           A command-line tool for running tests
        psed            A Perl implementation of sed
        ptar            A Perl implementation of tar
        ptardiff        A diff for tar archives
        s2p             sed-to-perl translator
        shasum          A tool to print or check SHA checksums
        splain          Describe Perl warnings and errors
        xsubpp          Compiler to convert Perl XS code into C code

    library files

                        in $privlib and $archlib specified to
                        Configure, usually under /usr/local/lib/perl5/.

    documentation

        man pages       in $man1dir, usually /usr/local/man/man1.
        module man
        pages           in $man3dir, usually /usr/local/man/man3.
        pod/*.pod       in $privlib/pod/.

installperl will also create the directories listed above
in L<"Installation Directories">.

Perl's *.h header files and the libperl library are also installed
under $archlib so that any user may later build new modules, run the
optional Perl compiler, or embed the perl interpreter into another
program even if the Perl source is no longer available.

=head2 Installing only version-specific parts

Sometimes you only want to install the version-specific parts of the perl
installation.  For example, you may wish to install a newer version of
perl alongside an already installed production version without
disabling installation of new modules for the production version.
To only install the version-specific parts of the perl installation, run

        Configure -Dversiononly

or answer 'y' to the appropriate Configure prompt.  Alternatively,
you can just manually run

        ./perl installperl -v

and skip installman altogether.

See also L<"Maintaining completely separate versions"> for another
approach.

=head1 cd /usr/include; h2ph *.h sys/*.h

Some perl scripts need to be able to obtain information from the
system header files.  This command will convert the most commonly used
header files in /usr/include into files that can be easily interpreted
by perl.  These files will be placed in the architecture-dependent
library ($archlib) directory you specified to Configure.

Note:  Due to differences in the C and perl languages, the conversion
of the header files is not perfect.  You will probably have to
hand-edit some of the converted files to get them to parse correctly.
For example, h2ph breaks spectacularly on type casting and certain
structures.

=head1 installhtml --help

Some sites may wish to make perl documentation available in HTML
format.  The installhtml utility can be used to convert pod
documentation into linked HTML files and install them.

Currently, the supplied ./installhtml script does not make use of the
html Configure variables.  This should be fixed in a future release.

The following command-line is an example of one used to convert
perl documentation:

  ./installhtml                   \
      --podroot=.                 \
      --podpath=lib:ext:pod:vms   \
      --recurse                   \
      --htmldir=/perl/nmanual     \
      --htmlroot=/perl/nmanual    \
      --splithead=pod/perlipc     \
      --splititem=pod/perlfunc    \
      --libpods=perlfunc:perlguts:perlvar:perlrun:perlop \
      --verbose

See the documentation in installhtml for more details.  It can take
many minutes to execute a large installation and you should expect to
see warnings like "no title", "unexpected directive" and "cannot
resolve" as the files are processed. We are aware of these problems
(and would welcome patches for them).

You may find it helpful to run installhtml twice. That should reduce
the number of "cannot resolve" warnings.

=head1 cd pod && make tex && (process the latex files)

Some sites may also wish to make the documentation in the pod/ directory
available in TeX format.  Type

        (cd pod && make tex && <process the latex files>)

=head1 Starting all over again

If you wish to re-build perl from the same build directory, you should
clean it out with the command

        make distclean

or

        make realclean

The only difference between the two is that make distclean also removes
your old config.sh and Policy.sh files.

If you are upgrading from a previous version of perl, or if you
change systems or compilers or make other significant changes, or if
you are experiencing difficulties building perl, you should not re-use
your old config.sh.

If your reason to reuse your old config.sh is to save your particular
installation choices, then you can probably achieve the same effect by
using the Policy.sh file.  See the section on L<"Site-wide Policy
settings"> above.

=head1 Reporting Problems

Wherever possible please use the perlbug tool supplied with this Perl
to report problems, as it automatically includes summary configuration
information about your perl, which may help us track down problems far
more quickly. But first you should read the advice in this file,
carefully re-read the error message and check the relevant manual pages
on your system, as these may help you find an immediate solution.  If
you are not sure whether what you are seeing is a bug, you can send a
message describing the problem to the comp.lang.perl.misc newsgroup to
get advice.

The perlbug tool is installed along with perl, so after you have
completed C<make install> it should be possible to run it with plain
C<perlbug>.  If the install fails, or you want to report problems with
C<make test> without installing perl, then you can use C<make nok> to
run perlbug to report the problem, or run it by hand from this source
directory with C<./perl -Ilib utils/perlbug>

If the build fails too early to run perlbug uninstalled, then please
B<run> the C<./myconfig> shell script, and mail its output along with
an accurate description of your problem to perlbug@perl.org

If Configure itself fails, and does not generate a config.sh file
(needed to run C<./myconfig>), then please mail perlbug@perl.org the
description of how Configure fails along with details of your system
- for example the output from running C<uname -a>

Please try to make your message brief but clear.  Brief, clear bug
reports tend to get answered more quickly.  Please don't worry if your
written English is not great - what matters is how well you describe
the important technical details of the problem you have encountered,
not whether your grammar and spelling is flawless.

Trim out unnecessary information.  Do not include large files (such as
config.sh or a complete Configure or make log) unless absolutely
necessary.  Do not include a complete transcript of your build
session.  Just include the failing commands, the relevant error
messages, and whatever preceding commands are necessary to give the
appropriate context.  Plain text should usually be sufficient--fancy
attachments or encodings may actually reduce the number of people who
read your message.  Your message will get relayed to over 400
subscribers around the world so please try to keep it brief but clear.

If you are unsure what makes a good bug report please read "How to
report Bugs Effectively" by Simon Tatham:
http://www.chiark.greenend.org.uk/~sgtatham/bugs.html

=head1 Coexistence with earlier versions of perl 5

Perl 5.10 is not binary compatible with earlier versions of Perl.
In other words, you will have to recompile your XS modules.

In general, you can usually safely upgrade from one version of Perl (e.g.
5.X.Y) to another similar minor version (e.g. 5.X.(Y+1))) without
re-compiling all of your extensions.  You can also safely leave the old
version around in case the new version causes you problems for some reason.

Usually, most extensions will probably not need to be recompiled to be
used with a newer version of Perl.  Here is how it is supposed to work.
(These examples assume you accept all the Configure defaults.)

Suppose you already have version 5.8.7 installed.  The directories
searched by 5.8.7 are typically like:

        /usr/local/lib/perl5/5.8.7/$archname
        /usr/local/lib/perl5/5.8.7
        /usr/local/lib/perl5/site_perl/5.8.7/$archname
        /usr/local/lib/perl5/site_perl/5.8.7

Now, suppose you install version 5.8.8.  The directories
searched by version 5.8.8 will be:

        /usr/local/lib/perl5/5.8.8/$archname
        /usr/local/lib/perl5/5.8.8
        /usr/local/lib/perl5/site_perl/5.8.8/$archname
        /usr/local/lib/perl5/site_perl/5.8.8

        /usr/local/lib/perl5/site_perl/5.8.7/$archname
        /usr/local/lib/perl5/site_perl/5.8.7
        /usr/local/lib/perl5/site_perl/

Notice the last three entries -- Perl understands the default structure
of the $sitelib directories and will look back in older, compatible
directories.  This way, modules installed under 5.8.7 will continue
to be usable by 5.8.7 but will also accessible to 5.8.8.  Further,
suppose that you upgrade a module to one which requires features
present only in 5.8.8.  That new module will get installed into
/usr/local/lib/perl5/site_perl/5.8.8 and will be available to 5.8.8,
but will not interfere with the 5.8.7 version.

The last entry, /usr/local/lib/perl5/site_perl/, is there so that
5.6.0 and above will look for 5.004-era pure perl modules.

Lastly, suppose you now install 5.10.0, which is not binary compatible
with 5.8.x.  The directories searched by 5.10.0 (if you don't change the
Configure defaults) will be:

        /usr/local/lib/perl5/5.10.0/$archname
        /usr/local/lib/perl5/5.10.0
        /usr/local/lib/perl5/site_perl/5.10.0/$archname
        /usr/local/lib/perl5/site_perl/5.10.0

        /usr/local/lib/perl5/site_perl/5.8.8

        /usr/local/lib/perl5/site_perl/5.8.7

        /usr/local/lib/perl5/site_perl/

Note that the earlier $archname entries are now gone, but pure perl
modules from earlier versions will still be found.

This way, you can choose to share compatible extensions, but also upgrade
to a newer version of an extension that may be incompatible with earlier
versions, without breaking the earlier versions' installations.

=head2 Maintaining completely separate versions

Many users prefer to keep all versions of perl in completely
separate directories.  This guarantees that an update to one version
won't interfere with another version.  (The defaults guarantee this for
libraries after 5.6.0, but not for executables. TODO?)  One convenient
way to do this is by using a separate prefix for each version, such as

        sh Configure -Dprefix=/opt/perl5.10.0

and adding /opt/perl5.10.0/bin to the shell PATH variable.  Such users
may also wish to add a symbolic link /usr/local/bin/perl so that
scripts can still start with #!/usr/local/bin/perl.

Others might share a common directory for maintenance sub-versions
(e.g. 5.10 for all 5.10.x versions), but change directory with
each major version.

If you are installing a development subversion, you probably ought to
seriously consider using a separate directory, since development
subversions may not have all the compatibility wrinkles ironed out
yet.

=head2 Upgrading from 5.8.x or earlier

B<Perl 5.10.0 is binary incompatible with Perl 5.8.x and any earlier
Perl release.>  Perl modules having binary parts
(meaning that a C compiler is used) will have to be recompiled to be
used with 5.10.0.  If you find you do need to rebuild an extension with
5.10.0, you may safely do so without disturbing the older
installations.  (See L<"Coexistence with earlier versions of perl 5">
above.)

See your installed copy of the perllocal.pod file for a (possibly
incomplete) list of locally installed modules.  Note that you want
perllocal.pod, not perllocale.pod, for installed module information.

=head1 Minimizing the Perl installation

The following section is meant for people worrying about squeezing the
Perl installation into minimal systems (for example when installing
operating systems, or in really small filesystems).

Leaving out as many extensions as possible is an obvious way:
Encode, with its big conversion tables, consumes a lot of
space.  On the other hand, you cannot throw away everything.  The
Fcntl module is pretty essential.  If you need to do network
programming, you'll appreciate the Socket module, and so forth: it all
depends on what do you need to do.

In the following we offer two different slimmed down installation
recipes.  They are informative, not normative: the choice of files
depends on what you need.

Firstly, the bare minimum to run this script

  use strict;
  use warnings;
  foreach my $f (</*>) {
     print("$f\n");
  }

in Linux is as follows (under $Config{prefix}):

  ./bin/perl
  ./lib/perl5/5.9.3/strict.pm
  ./lib/perl5/5.9.3/warnings.pm
  ./lib/perl5/5.9.3/i686-linux/File/Glob.pm
  ./lib/perl5/5.9.3/i686-linux/XSLoader.pm
  ./lib/perl5/5.9.3/i686-linux/auto/File/Glob/Glob.so

Secondly, Debian perl-base package contains the following files,
size about 1.9MB in its i386 version:

  /usr/bin/perl
  /usr/bin/perl5.8.4
  /usr/lib/perl/5.8
  /usr/lib/perl/5.8.4/B.pm
  /usr/lib/perl/5.8.4/B/Deparse.pm
  /usr/lib/perl/5.8.4/Config.pm
  /usr/lib/perl/5.8.4/Cwd.pm
  /usr/lib/perl/5.8.4/Data/Dumper.pm
  /usr/lib/perl/5.8.4/DynaLoader.pm
  /usr/lib/perl/5.8.4/Errno.pm
  /usr/lib/perl/5.8.4/Fcntl.pm
  /usr/lib/perl/5.8.4/File/Glob.pm
  /usr/lib/perl/5.8.4/IO.pm
  /usr/lib/perl/5.8.4/IO/File.pm
  /usr/lib/perl/5.8.4/IO/Handle.pm
  /usr/lib/perl/5.8.4/IO/Pipe.pm
  /usr/lib/perl/5.8.4/IO/Seekable.pm
  /usr/lib/perl/5.8.4/IO/Select.pm
  /usr/lib/perl/5.8.4/IO/Socket.pm
  /usr/lib/perl/5.8.4/POSIX.pm
  /usr/lib/perl/5.8.4/Socket.pm
  /usr/lib/perl/5.8.4/XSLoader.pm
  /usr/lib/perl/5.8.4/auto/Cwd/Cwd.bs
  /usr/lib/perl/5.8.4/auto/Cwd/Cwd.so
  /usr/lib/perl/5.8.4/auto/Data/Dumper/Dumper.bs
  /usr/lib/perl/5.8.4/auto/Data/Dumper/Dumper.so
  /usr/lib/perl/5.8.4/auto/DynaLoader/DynaLoader.a
  /usr/lib/perl/5.8.4/auto/DynaLoader/autosplit.ix
  /usr/lib/perl/5.8.4/auto/DynaLoader/dl_expandspec.al
  /usr/lib/perl/5.8.4/auto/DynaLoader/dl_find_symbol_anywhere.al
  /usr/lib/perl/5.8.4/auto/DynaLoader/dl_findfile.al
  /usr/lib/perl/5.8.4/auto/DynaLoader/extralibs.ld
  /usr/lib/perl/5.8.4/auto/Fcntl/Fcntl.bs
  /usr/lib/perl/5.8.4/auto/Fcntl/Fcntl.so
  /usr/lib/perl/5.8.4/auto/File/Glob/Glob.bs
  /usr/lib/perl/5.8.4/auto/File/Glob/Glob.so
  /usr/lib/perl/5.8.4/auto/IO/IO.bs
  /usr/lib/perl/5.8.4/auto/IO/IO.so
  /usr/lib/perl/5.8.4/auto/POSIX/POSIX.bs
  /usr/lib/perl/5.8.4/auto/POSIX/POSIX.so
  /usr/lib/perl/5.8.4/auto/POSIX/autosplit.ix
  /usr/lib/perl/5.8.4/auto/POSIX/load_imports.al
  /usr/lib/perl/5.8.4/auto/Socket/Socket.bs
  /usr/lib/perl/5.8.4/auto/Socket/Socket.so
  /usr/lib/perl/5.8.4/lib.pm
  /usr/lib/perl/5.8.4/re.pm
  /usr/share/doc/perl-base
  /usr/share/doc/perl/AUTHORS.gz
  /usr/share/doc/perl/Documentation
  /usr/share/doc/perl/README.Debian.gz
  /usr/share/doc/perl/changelog.Debian.gz
  /usr/share/doc/perl/copyright
  /usr/share/man/man1/perl.1.gz
  /usr/share/perl/5.8
  /usr/share/perl/5.8.4/AutoLoader.pm
  /usr/share/perl/5.8.4/Carp.pm
  /usr/share/perl/5.8.4/Carp/Heavy.pm
  /usr/share/perl/5.8.4/Exporter.pm
  /usr/share/perl/5.8.4/Exporter/Heavy.pm
  /usr/share/perl/5.8.4/File/Spec.pm
  /usr/share/perl/5.8.4/File/Spec/Unix.pm
  /usr/share/perl/5.8.4/FileHandle.pm
  /usr/share/perl/5.8.4/Getopt/Long.pm
  /usr/share/perl/5.8.4/IO/Socket/INET.pm
  /usr/share/perl/5.8.4/IO/Socket/UNIX.pm
  /usr/share/perl/5.8.4/IPC/Open2.pm
  /usr/share/perl/5.8.4/IPC/Open3.pm
  /usr/share/perl/5.8.4/List/Util.pm
  /usr/share/perl/5.8.4/Scalar/Util.pm
  /usr/share/perl/5.8.4/SelectSaver.pm
  /usr/share/perl/5.8.4/Symbol.pm
  /usr/share/perl/5.8.4/Text/ParseWords.pm
  /usr/share/perl/5.8.4/Text/Tabs.pm
  /usr/share/perl/5.8.4/Text/Wrap.pm
  /usr/share/perl/5.8.4/attributes.pm
  /usr/share/perl/5.8.4/base.pm
  /usr/share/perl/5.8.4/bytes.pm
  /usr/share/perl/5.8.4/bytes_heavy.pl
  /usr/share/perl/5.8.4/constant.pm
  /usr/share/perl/5.8.4/fields.pm
  /usr/share/perl/5.8.4/integer.pm
  /usr/share/perl/5.8.4/locale.pm
  /usr/share/perl/5.8.4/overload.pm
  /usr/share/perl/5.8.4/strict.pm
  /usr/share/perl/5.8.4/utf8.pm
  /usr/share/perl/5.8.4/utf8_heavy.pl
  /usr/share/perl/5.8.4/vars.pm
  /usr/share/perl/5.8.4/warnings.pm
  /usr/share/perl/5.8.4/warnings/register.pm

A nice trick to find out the minimal set of Perl library files you will
need to run a Perl program is

   perl -e 'do "prog.pl"; END { print "$_\n" for sort keys %INC }'

(this will not find libraries required in runtime, unfortunately, but
it's a minimal set) and if you want to find out all the files you can
use something like the below

   strace perl -le 'do "x.pl"' 2>&1 | perl -nle '/^open\(\"(.+?)"/ && print $1'

(The 'strace' is Linux-specific, other similar utilities include 'truss'
and 'ktrace'.)

=head2 C<-DNO_MATHOMS>

If you configure perl with C<-Accflags=-DNO_MATHOMS>, the functions from
F<mathoms.c> will not be compiled in. Those functions are no longer used
by perl itself; for source compatibility reasons, though, they weren't
completely removed.

=head1 DOCUMENTATION

Read the manual entries before running perl.  The main documentation
is in the pod/ subdirectory and should have been installed during the
build process.  Type B<man perl> to get started.  Alternatively, you
can type B<perldoc perl> to use the supplied perldoc script.  This is
sometimes useful for finding things in the library modules.

=head1 AUTHOR

Original author:  Andy Dougherty doughera@lafayette.edu , borrowing very
heavily from the original README by Larry Wall, with lots of helpful
feedback and additions from the perl5-porters@perl.org folks.

If you have problems, corrections, or questions, please see
L<"Reporting Problems"> above.

=head1 REDISTRIBUTION

This document is part of the Perl package and may be distributed under
the same terms as perl itself, with the following additional request:
If you are distributing a modified version of perl (perhaps as part of
a larger package) please B<do> modify these installation instructions
and the contact information to match your distribution.