Интерактивная система просмотра системных руководств (man-ов)
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perlhack - How to hack at the Perl internals
This document attempts to explain how Perl development takes
place, and ends with some suggestions for people wanting to
become bona fide porters.
The perl5-porters mailing list is where the Perl standard
distribution is maintained and developed. The list can get
anywhere from 10 to 150 messages a day, depending on the
heatedness of the debate. Most days there are two or three
patches, extensions, features, or bugs being discussed at a
A searchable archive of the list is at:
The list is also archived under the usenet group name
List subscribers (the porters themselves) come in several
flavours. Some are quiet curious lurkers, who rarely pitch
in and instead watch the ongoing development to ensure
they're forewarned of new changes or features in Perl. Some
are representatives of vendors, who are there to make sure
that Perl continues to compile and work on their platforms.
Some patch any reported bug that they know how to fix, some
are actively patching their pet area (threads, Win32, the
regexp engine), while others seem to do nothing but
complain. In other words, it's your usual mix of technical
Over this group of porters presides Larry Wall. He has the
final word in what does and does not change in the Perl
language. Various releases of Perl are shepherded by a
``pumpking'', a porter responsible for gathering patches,
deciding on a patch-by-patch feature-by-feature basis what
will and will not go into the release. For instance,
Gurusamy Sarathy is the pumpking for the 5.6 release of
In addition, various people are pumpkings for different
things. For instance, Andy Dougherty and Jarkko Hietaniemi
share the Configure pumpkin, and Tom Christiansen is the
Larry sees Perl development along the lines of the US
government: there's the Legislature (the porters), the
Executive branch (the pumpkings), and the Supreme Court
(Larry). The legislature can discuss and submit patches to
the executive branch all they like, but the executive branch
is free to veto them. Rarely, the Supreme Court will side
with the executive branch over the legislature, or the
legislature over the executive branch. Mostly, however, the
legislature and the executive branch are supposed to get
along and work out their differences without impeachment or
You might sometimes see reference to Rule 1 and Rule 2.
Larry's power as Supreme Court is expressed in The Rules:
1 Larry is always by definition right about how Perl
should behave. This means he has final veto power on
the core functionality.
2 Larry is allowed to change his mind about any matter at
a later date, regardless of whether he previously
invoked Rule 1.
Got that? Larry is always right, even when he was wrong.
It's rare to see either Rule exercised, but they are often
New features and extensions to the language are contentious,
because the criteria used by the pumpkings, Larry, and other
porters to decide which features should be implemented and
incorporated are not codified in a few small design goals as
with some other languages. Instead, the heuristics are
flexible and often difficult to fathom. Here is one
person's list, roughly in decreasing order of importance, of
heuristics that new features have to be weighed against:
Does concept match the general goals of Perl?
These haven't been written anywhere in stone, but one
1. Keep it fast, simple, and useful.
2. Keep features/concepts as orthogonal as possible.
3. No arbitrary limits (platforms, data sizes, cultures).
4. Keep it open and exciting to use/patch/advocate Perl everywhere.
5. Either assimilate new technologies, or build bridges to them.
Where is the implementation?
All the talk in the world is useless without an
implementation. In almost every case, the person or
people who argue for a new feature will be expected to
be the ones who implement it. Porters capable of coding
new features have their own agendas, and are not
available to implement your (possibly good) idea.
It's a cardinal sin to break existing Perl programs.
New warnings are contentious--some say that a program
that emits warnings is not broken, while others say it
is. Adding keywords has the potential to break
programs, changing the meaning of existing token
sequences or functions might break programs.
Could it be a module instead?
Perl 5 has extension mechanisms, modules and XS,
specifically to avoid the need to keep changing the Perl
interpreter. You can write modules that export
functions, you can give those functions prototypes so
they can be called like built-in functions, you can even
write XS code to mess with the runtime data structures
of the Perl interpreter if you want to implement really
complicated things. If it can be done in a module
instead of in the core, it's highly unlikely to be
Is the feature generic enough?
Is this something that only the submitter wants added to
the language, or would it be broadly useful? Sometimes,
instead of adding a feature with a tight focus, the
porters might decide to wait until someone implements
the more generalized feature. For instance, instead of
implementing a ``delayed evaluation'' feature, the
porters are waiting for a macro system that would permit
delayed evaluation and much more.
Does it potentially introduce new bugs?
Radical rewrites of large chunks of the Perl interpreter
have the potential to introduce new bugs. The smaller
and more localized the change, the better.
Does it preclude other desirable features?
A patch is likely to be rejected if it closes off future
avenues of development. For instance, a patch that
placed a true and final interpretation on prototypes is
likely to be rejected because there are still options
for the future of prototypes that haven't been
Is the implementation robust?
Good patches (tight code, complete, correct) stand more
chance of going in. Sloppy or incorrect patches might
be placed on the back burner until the pumpking has time
to fix, or might be discarded altogether without further
Is the implementation generic enough to be portable?
The worst patches make use of a system-specific
features. It's highly unlikely that nonportable
additions to the Perl language will be accepted.
Is there enough documentation?
Patches without documentation are probably ill-thought
out or incomplete. Nothing can be added without
documentation, so submitting a patch for the appropriate
manpages as well as the source code is always a good
idea. If appropriate, patches should add to the test
suite as well.
Is there another way to do it?
Larry said ``Although the Perl Slogan is There's More
Than One Way to Do It, I hesitate to make 10 ways to do
something''. This is a tricky heuristic to navigate,
though--one man's essential addition is another man's
Does it create too much work?
Work for the pumpking, work for Perl programmers, work
for module authors, ... Perl is supposed to be easy.
Patches speak louder than words
Working code is always preferred to pie-in-the-sky
ideas. A patch to add a feature stands a much higher
chance of making it to the language than does a random
feature request, no matter how fervently argued the
request might be. This ties into ``Will it be
useful?'', as the fact that someone took the time to
make the patch demonstrates a strong desire for the
If you're on the list, you might hear the word ``core''
bandied around. It refers to the standard distribution.
``Hacking on the core'' means you're changing the C source
code to the Perl interpreter. ``A core module'' is one that
ships with Perl.
The source code to the Perl interpreter, in its different
versions, is kept in a repository managed by a revision
control system (which is currently the Perforce program, see
http://perforce.com/). The pumpkings and a few others have
access to the repository to check in changes. Periodically
the pumpking for the development version of Perl will
release a new version, so the rest of the porters can see
what's changed. The current state of the main trunk of
repository, and patches that describe the individual changes
that have happened since the last public release are
available at this location:
Selective parts are also visible via the rsync protocol. To
get all the individual changes to the mainline since the
last development release, use the following command:
rsync -avuz rsync://ftp.linux.activestate.com/perl-diffs perl-diffs
Use this to get the latest source tree in full:
rsync -avuz rsync://ftp.linux.activestate.com/perl-current perl-current
Needless to say, the source code in perl-current is usually
in a perpetual state of evolution. You should expect it to
be very buggy. Do not use it for any purpose other than
testing and development.
Always submit patches to email@example.com. This lets
other porters review your patch, which catches a surprising
number of errors in patches. Either use the diff program
(available in source code form from
ftp://ftp.gnu.org/pub/gnu/), or use Johan Vromans' makepatch
(available from CPAN/authors/id/JV/). Unified diffs are
preferred, but context diffs are accepted. Do not send
RCS-style diffs or diffs without context lines. More
information is given in the Porting/patching.pod file in the
Perl source distribution. Please patch against the latest
development version (e.g., if you're fixing a bug in the
5.005 track, patch against the latest 5.005_5x version).
Only patches that survive the heat of the development branch
get applied to maintenance versions.
Your patch should update the documentation and test suite.
To report a bug in Perl, use the program perlbug which comes
with Perl (if you can't get Perl to work, send mail to the
address firstname.lastname@example.org or email@example.com). Reporting
bugs through perlbug feeds into the automated bug-tracking
system, access to which is provided through the web at
http://bugs.perl.org/. It often pays to check the archives
of the perl5-porters mailing list to see whether the bug
you're reporting has been reported before, and if so whether
it was considered a bug. See above for the location of the
The CPAN testers (http://testers.cpan.org/) are a group of
volunteers who test CPAN modules on a variety of platforms.
Perl Labs (http://labs.perl.org/) automatically tests Perl
source releases on platforms and gives feedback to the CPAN
testers mailing list. Both efforts welcome volunteers.
To become an active and patching Perl porter, you'll need to
learn how Perl works on the inside. Chip Salzenberg, a
pumpking, has written articles on Perl internals for The
Perl Journal (http://www.tpj.com/) which explain how various
parts of the Perl interpreter work. The `perlguts' manpage
explains the internal data structures. And, of course, the
C source code (sometimes sparsely commented, sometimes
commented well) is a great place to start (begin with
`perl.c' and see where it goes from there). A lot of the
style of the Perl source is explained in the
Porting/pumpkin.pod file in the source distribution.
It is essential that you be comfortable using a good
debugger (e.g. gdb, dbx) before you can patch perl.
Stepping through perl as it executes a script is perhaps the
best (if sometimes tedious) way to gain a precise
understanding of the overall architecture of the language.
If you build a version of the Perl interpreter with
`-DDEBUGGING', Perl's -D command line flag will cause
copious debugging information to be emitted (see the
`perlrun' manpage). If you build a version of Perl with
compiler debugging information (e.g. with the C compiler's
`-g' option instead of `-O') then you can step through the
execution of the interpreter with your favourite C symbolic
debugger, setting breakpoints on particular functions.
It's a good idea to read and lurk for a while before
chipping in. That way you'll get to see the dynamic of the
conversations, learn the personalities of the players, and
hopefully be better prepared to make a useful contribution
when do you speak up.
If after all this you still think you want to join the
perl5-porters mailing list, send mail to perl5-porters-
firstname.lastname@example.org. To unsubscribe, send mail to
This document was written by Nathan Torkington, and is
maintained by the perl5-porters mailing list.