=encoding utf8
=
for
comment
Consistent formatting of this file is achieved
with
:
perl ./Porting/podtidy pod/perlhack.pod
=head1 NAME
perlhack - How to hack on Perl
=head1 DESCRIPTION
This document explains how Perl development works. It includes details
about the Perl 5 Porters email list, the Perl repository, the Perlbug
bug tracker, patch guidelines, and commentary on Perl development
philosophy.
=head1 SUPER QUICK PATCH GUIDE
If you just want to submit a single small patch like a pod fix, a test
for
a bug, comment fixes, etc., it
's easy! Here'
s how:
=over 4
=item * Check out the source repository
The perl source is in a git repository. You can clone the repository
with
the following command:
=item * Make your change
Hack, hack, hack.
=item * Test your change
You can run all the tests
with
the following commands:
% ./Configure -des -Dusedevel
% make test
Keep hacking
until
the tests pass.
=item * Commit your change
Committing your work will save the change I<on your
local
system
>:
% git commit -a -m
'Commit message goes here'
Make sure the commit message describes your change in a single
sentence. For example,
"Fixed spelling errors in perlhack.pod"
.
=item * Send your change to perlbug
The
next
step is to submit your patch to the Perl core ticket
system
via email.
Assuming your patch consists of a single git commit, the following
writes the file as a MIME attachment, and sends it
with
a meaningful
subject:
% git
format
-patch -1 --attach
% perlbug -s
"[PATCH] $(git log -1 --oneline HEAD)"
-f 0001-*.patch
The perlbug program will ask you a few questions about your email
address and the patch you
're submitting. Once you'
ve answered them it
will submit your patch via email.
=item * Thank you
The porters appreciate the
time
you spent helping to make Perl better.
Thank you!
=back
=head1 BUG REPORTING
If you want to report a bug in Perl, you must
use
the F<perlbug>
command line tool. This tool will ensure that your bug report includes
all the relevant
system
and configuration information.
To browse existing Perl bugs and patches, you can
use
the web interface
Please check the archive of the perl5-porters list (see below) and/or
the bug tracking
system
before
submitting a bug report. Often, you'll
find that the bug
has
been reported already.
You can
log
in to the bug tracking
system
and comment on existing bug
reports. If you have additional information regarding an existing bug,
please add it. This will help the porters fix the bug.
=head1 PERL 5 PORTERS
The perl5-porters (p5p) mailing list is where the Perl standard
distribution is maintained and developed. The people who maintain Perl
are also referred to as the
"Perl 5 Porters"
,
"p5p"
or just the
"porters"
.
A searchable archive of the list is available at
also another archive at
=head2 perl-changes mailing list
The perl5-changes mailing list receives a copy of
each
patch that gets
submitted to the maintenance and development branches of the perl
subscription and archive information.
=head2
Feel free to
join
the channel and ask questions about hacking on the
Perl core.
=head1 GETTING THE PERL SOURCE
All of Perl's source code is kept centrally in a Git repository at
I<perl5.git.perl.org>. The repository contains many Perl revisions from
Perl 1 onwards and all the revisions from Perforce, the previous
version control
system
.
For much more detail on using git
with
the Perl repository, please see
L<perlgit>.
=head2 Read access via Git
You will need a copy of Git
for
your computer. You can fetch a copy of
the repository using the git protocol:
This clones the repository and makes a
local
copy in the F<perl>
directory.
If you cannot
use
the git protocol
for
firewall reasons, you can also
clone via http, though this is much slower:
=head2 Read access via the web
You may access the repository over the web. This allows you to browse
the tree, see recent commits, subscribe to RSS feeds
for
the changes,
search
for
particular commits and more. You may access it at
=head2 Read access via rsync
You can also choose to
use
rsync to get a copy of the current source
tree
for
the bleadperl branch and all maintenance branches:
(Add the C<--
delete
> option to remove leftover files.)
To get a full list of the available sync points:
% rsync perl5.git.perl.org::
=head2 Write access via git
If you have a commit bit, please see L<perlgit>
for
more details on
using git.
=head1 PATCHING PERL
If you're planning to
do
more extensive work than a single small fix,
we encourage you to
read
the documentation below. This will help you
focus your work and make your patches easier to incorporate into the
Perl source.
=head2 Submitting patches
If you have a small patch to submit, please submit it via perlbug. You
can also
send
email directly to perlbug
@perl
.org. Please note that
messages sent to perlbug may be held in a moderation queue, so you
won't receive a response immediately.
You'll know your submission
has
been processed
when
you receive an
email from
our
ticket tracking
system
. This email will give you a
ticket number. Once your patch
has
made it to the ticket tracking
system
, it will also be sent to the perl5-porters
@perl
.org list.
Patches are reviewed and discussed on the p5p list. Simple,
uncontroversial patches will usually be applied without any discussion.
When the patch is applied, the ticket will be updated and you will
receive email. In addition, an email will be sent to the p5p list.
In other cases, the patch will need more work or discussion. That will
happen on the p5p list.
You are encouraged to participate in the discussion and advocate
for
your patch. Sometimes your patch may get lost in the shuffle. It's
appropriate to
send
a reminder email to p5p
if
no
action
has
been taken
in a month. Please remember that the Perl 5 developers are all
volunteers, and be polite.
Changes are always applied directly to the main development branch,
called
"blead"
. Some patches may be backported to a maintenance branch.
If you think your patch is appropriate
for
the maintenance branch,
please explain why
when
you submit it.
=head2 Getting your patch accepted
If you are submitting a code patch there are several things that you
can
do
to help the Perl 5 Porters
accept
your patch.
=head3 Patch style
If you used git to check out the Perl source, then using C<git
format
-patch> will produce a patch in a style suitable
for
Perl. The
C<
format
-patch> command produces one patch file
for
each
commit you
made. If you prefer to
send
a single patch
for
all commits, you can
use
C<git diff>.
% git checkout blead
% git pull
% git diff blead
my
-branch-name
This produces a patch based on the difference between blead and your
current branch. It's important to make sure that blead is up to date
before
producing the diff, that's why we call C<git pull> first.
We strongly recommend that you
use
git
if
possible. It will make your
life easier, and ours as well.
However,
if
you're not using git, you can still produce a suitable
patch. You'll need a pristine copy of the Perl source to diff against.
The porters prefer unified diffs. Using GNU C<diff>, you can produce a
diff like this:
% diff -Npurd perl.pristine perl.mine
Make sure that you C<make realclean> in your copy of Perl to remove any
build artifacts, or you may get a confusing result.
=head3 Commit message
As you craft
each
patch you intend to submit to the Perl core, it's
important to
write
a good commit message. This is especially important
if
your submission will consist of a series of commits.
The first line of the commit message should be a short description
without a period. It should be
no
longer than the subject line of an
email, 50 characters being a good rule of thumb.
A lot of Git tools (Gitweb, GitHub, git
log
--pretty=oneline, ...) will
only display the first line (cut off at 50 characters)
when
presenting
commit summaries.
The commit message should include a description of the problem that the
patch corrects or new functionality that the patch adds.
As a general rule of thumb, your commit message should help a
programmer who knows the Perl core quickly understand what you were
trying to
do
, how you were trying to
do
it, and why the change matters
to Perl.
=over 4
=item * Why
Your commit message should describe why the change you are making is
important. When someone looks at your change in six months or six
years, your intent should be clear.
If you're deprecating a feature
with
the intent of later simplifying
another bit of code,
say
so. If you're fixing a performance problem or
adding a new feature to support some other bit of the core, mention
that.
=item * What
Your commit message should describe what part of the Perl core you're
changing and what you expect your patch to
do
.
=item * How
While it's not necessary
for
documentation changes, new tests or
trivial patches, it's often worth explaining how your change works.
Even
if
it's clear to you today, it may not be clear to a porter
next
month or
next
year.
=back
A commit message isn't intended to take the place of comments in your
code. Commit messages should describe the change you made,
while
code
comments should describe the current state of the code.
If you've just implemented a new feature, complete
with
doc, tests and
well-commented code, a brief commit message will often suffice. If,
however, you've just changed a single character deep in the parser or
lexer, you might need to
write
a small novel to ensure that future
readers understand what you did and why you did it.
=head3 Comments, Comments, Comments
Be sure to adequately comment your code. While commenting every line is
unnecessary, anything that takes advantage of side effects of
operators, that creates changes that will be felt outside of the
function being patched, or that others may find confusing should be
documented. If you are going to err, it is better to err on the side of
adding too many comments than too few.
The best comments explain I<why> the code does what it does, not I<what
it does>.
=head3 Style
In general, please follow the particular style of the code you are
patching.
In particular, follow these general guidelines
for
patching Perl
sources:
=over 4
=item *
8-wide tabs (
no
exceptions!)
=item *
4-wide indents
for
code, 2-wide indents
for
nested CPP
=item *
Try hard not to exceed 79-columns
=item *
ANSI C prototypes
=item *
Uncuddled elses and
"K&R"
style
for
indenting control constructs
=item *
No C++ style (//) comments
=item *
Mark places that need to be revisited
with
XXX (and revisit often!)
=item *
Opening brace lines up
with
"if"
when
conditional spans multiple lines;
should be at end-of-line otherwise
=item *
In function definitions, name starts in column 0 (
return
value is on
previous line)
=item *
Single space
after
keywords that are followed by parens,
no
space
between function name and following paren
=item *
Avoid assignments in conditionals, but
if
they're unavoidable,
use
extra paren, e.g.
"if (a && (b = c)) ..."
=item *
"return foo;"
rather than
"return(foo);"
=item *
"if (!foo) ..."
rather than
"if (foo == FALSE) ..."
etc.
=back
=head3 Test suite
If your patch changes code (rather than just changing documentation),
you should also include one or more test cases which illustrate the bug
you
're fixing or validate the new functionality you'
re adding. In
general, you should update an existing test file rather than create a
new one.
Your test suite additions should generally follow these guidelines
(courtesy of Gurusamy Sarathy <gsar
@activestate
.com>):
=over 4
=item *
Know what you're testing. Read the docs, and the source.
=item *
Tend to fail, not succeed.
=item *
Interpret results strictly.
=item *
Use unrelated features (this will flush out bizarre interactions).
=item *
Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
=item *
Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
found in t/op/
tie
.t is much more maintainable, and gives better failure
reports).
=item *
Give meaningful error messages
when
a test fails.
=item *
Avoid using
qx//
and
system
()
unless
you are testing
for
them. If you
do
use
them, make sure that you cover _all_ perl platforms.
=item *
Unlink any temporary files you create.
=item *
Promote unforeseen warnings to errors
with
$SIG
{__WARN__}.
=item *
Be sure to
use
the libraries and modules shipped
with
the version being
tested, not those that were already installed.
=item *
Add comments to the code explaining what you are testing
for
.
=item *
Make updating the
'1..42'
string unnecessary. Or make sure that you
update it.
=item *
Test _all_ behaviors of a
given
operator, library, or function.
Test all optional arguments.
Test
return
values
in various contexts (boolean,
scalar
, list, lvalue).
Use both global and lexical variables.
Don't forget the exceptional, pathological cases.
=back
=head2 Patching a core module
This works just like patching anything
else
,
with
one extra
consideration.
Modules in the F<cpan/> directory of the source tree are maintained
outside of the Perl core. When the author updates the module, the
updates are simply copied into the core. See that module's
information on reporting bugs and submitting patches.
In most cases, patches to modules in F<cpan/> should be sent upstream
and should not be applied to the Perl core individually. If a patch to
a file in F<cpan/> absolutely cannot
wait
for
the fix to be made
upstream, released to CPAN and copied to blead, you must add (or
update) a C<CUSTOMIZED> entry in the F<
"Porting/Maintainers.pl"
> file
to flag that a
local
modification
has
been made. See
F<
"Porting/Maintainers.pl"
>
for
more details.
In contrast, modules in the F<dist/> directory are maintained in the
core.
=head2 Updating perldelta
For changes significant enough to warrant a F<pod/perldelta.pod> entry,
the porters will greatly appreciate it
if
you submit a delta entry
along
with
your actual change. Significant changes include, but are not
limited to:
=over 4
=item *
Adding, deprecating, or removing core features
=item *
Adding, deprecating, removing, or upgrading core or dual-life modules
=item *
Adding new core tests
=item *
Fixing security issues and user-visible bugs in the core
=item *
Changes that might break existing code, either on the perl or C level
=item *
Significant performance improvements
=item *
Adding, removing, or significantly changing documentation in the
F<pod/> directory
=item *
Important platform-specific changes
=back
Please make sure you add the perldelta entry to the right section
within F<pod/perldelta.pod>. More information on how to
write
good
perldelta entries is available in the C<Style> section of
F<Porting/how_to_write_a_perldelta.pod>.
=head2 What makes
for
a good patch?
New features and extensions to the language can be contentious. There
is
no
specific set of criteria which determine what features get added,
but here are some questions to consider
when
developing a patch:
=head3 Does the concept match the general goals of Perl?
Our goals include, but are not limited to:
=over 4
=item 1.
Keep it fast, simple, and useful.
=item 2.
Keep features/concepts as orthogonal as possible.
=item 3.
No arbitrary limits (platforms, data sizes, cultures).
=item 4.
Keep it
open
and exciting to
use
/patch/advocate Perl everywhere.
=item 5.
Either assimilate new technologies, or build bridges to them.
=back
=head3 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.
=head3 Backwards compatibility
It's a cardinal
sin
to break existing Perl programs. New warnings can
be 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.
The Perl 5 core includes mechanisms to help porters make backwards
incompatible changes more compatible such as the L<feature> and
L<deprecate> modules. Please
use
them
when
appropriate.
=head3 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.
Whenever possible, new features should be prototyped in a CPAN module
before
they will be considered
for
the core.
=head3 Is the feature generic enough?
Is this something that only the submitter wants added to the language,
or is it 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.
=head3 Does it potentially introduce new bugs?
Radical rewrites of large chunks of the Perl interpreter have the
potential to introduce new bugs.
=head3 How big is it?
The smaller and more localized the change, the better. Similarly, a
series of small patches is greatly preferred over a single large patch.
=head3 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 addressed.
=head3 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 notice.
=head3 Is the implementation generic enough to be portable?
The worst patches make
use
of
system
-specific features. It's highly
unlikely that non-portable additions to the Perl language will be
accepted.
=head3 Is the implementation tested?
Patches which change behaviour (fixing bugs or introducing new
features) must include regression tests to verify that everything works
as expected.
Without tests provided by the original author, how can anyone
else
changing perl in the future be sure that they haven't unwittingly
broken the behaviour the patch implements? And without tests, how can
the patch's author be confident that his/her hard work put into the
patch won't be accidentally thrown away by someone in the future?
=head3 Is there enough documentation?
Patches without documentation are probably ill-thought out or
incomplete. No features can be added or changed without documentation,
so submitting a patch
for
the appropriate pod docs as well as the
source code is important.
=head3 Is there another way to
do
it?
Larry said "Although the Perl Slogan is I<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 pointless cruft.
=head3 Does it create too much work?
Work
for
the pumpking, work
for
Perl programmers, work
for
module
authors, ... Perl is supposed to be easy.
=head3 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 feature.
=head1 TESTING
The core uses the same testing style as the rest of Perl, a simple
"ok/not ok"
run through Test::Harness, but there are a few special
considerations.
There are three ways to
write
a test in the core. L<Test::More>,
F<t/test.pl> and ad hoc C<
print
$test
?
"ok 42\n"
:
"not ok 42\n"
>. The
decision of which to
use
depends on what part of the test suite you're
working on. This is a measure to prevent a high-level failure (such as
Config.pm breaking) from causing basic functionality tests to fail.
The F<t/test.pl> library provides some of the features of
L<Test::More>, but avoids loading most modules and uses as few core
features as possible.
If you
write
your own test,
use
the L<Test Anything
=over 4
=item * F<t/base> and F<t/comp>
Since we don't know
if
require
works, or even subroutines,
use
ad hoc
tests
for
these two. Step carefully to avoid using the feature being
tested.
=item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
Now that basic
require
() and subroutines are tested, you can
use
the
F<t/test.pl> library.
You can also
use
certain libraries like Config conditionally, but be
sure to skip the test gracefully
if
it's not there.
=item * Everything
else
Now that the core of Perl is tested, L<Test::More> can and should be
used. You can also
use
the full suite of core modules in the tests.
=back
When you
say
"make test"
, Perl uses the F<t/TEST> program to run the
test suite (except under Win32 where it uses F<t/harness> instead). All
tests are run from the F<t/> directory, B<not> the directory which
contains the test. This causes some problems
with
the tests in F<lib/>,
so here's some opportunity
for
some patching.
You must be triply conscious of cross-platform concerns. This usually
boils down to using L<File::Spec> and avoiding things like C<
fork
()>
and C<
system
()>
unless
absolutely necessary.
=head2 Special C<make test> targets
There are various special make targets that can be used to test Perl
slightly differently than the standard
"test"
target. Not all them are
expected to give a 100% success rate. Many of them have several
aliases, and many of them are not available on certain operating
systems.
=over 4
=item * test_porting
This runs some basic sanity tests on the source tree and helps
catch
basic errors
before
you submit a patch.
=item * coretest
Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests).
(Not available on Win32)
=item * test.deparse
Run all the tests through L<B::Deparse>. Not all tests will succeed.
(Not available on Win32)
=item * test.taintwarn
Run all tests
with
the B<-t> command-line switch. Not all tests are
expected to succeed (
until
they're specifically fixed, of course).
(Not available on Win32)
=item * minitest
Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
F<t/op>, F<t/uni> and F<t/mro> tests.
=item * test.valgrind check.valgrind utest.valgrind ucheck.valgrind
(Only in Linux) Run all the tests using the memory leak + naughty
memory access tool
"valgrind"
. The
log
files will be named
F<testname.valgrind>.
=item * test.torture torturetest
Run all the usual tests and some extra tests. As of Perl 5.8.0, the
only extra tests are Abigail's JAPHs, F<t/japh/abigail.t>.
You can also run the torture test
with
F<t/harness> by giving
C<-torture> argument to F<t/harness>.
=item * utest ucheck test.utf8 check.utf8
Run all the tests
with
-Mutf8. Not all tests will succeed.
(Not available on Win32)
=item * minitest.utf16 test.utf16
Runs the tests
with
UTF-16 encoded scripts, encoded
with
different
versions of this encoding.
C<make utest.utf16> runs the test suite
with
a combination of C<-utf8>
and C<-utf16> arguments to F<t/TEST>.
(Not available on Win32)
=item * test_harness
Run the test suite
with
the F<t/harness> controlling program, instead
of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
L<Test::Harness> module, thus using this test target supposes that perl
mostly works. The main advantage
for
our
purposes is that it prints a
detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it
doesn't redirect stderr to stdout.
Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
so there is
no
special
"test_harness"
target.
Under Win32's
"test"
target you may
use
the TEST_SWITCHES and
TEST_FILES environment variables to control the behaviour of
F<t/harness>. This means you can
say
nmake test TEST_FILES=
"op/*.t"
nmake test TEST_SWITCHES=
"-torture"
TEST_FILES=
"op/*.t"
=item * test-notty test_notty
Sets PERL_SKIP_TTY_TEST to true
before
running normal test.
=back
=head2 Parallel tests
The core distribution can now run its regression tests in parallel on
Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
in your environment to the number of tests to run in parallel, and run
C<make test_harness>. On a Bourne-like shell, this can be done as
TEST_JOBS=3 make test_harness
An environment variable is used, rather than parallel make itself,
because L<TAP::Harness> needs to be able to schedule individual
non-conflicting test scripts itself, and there is
no
standard interface
to C<make> utilities to interact
with
their job schedulers.
Note that currently some test scripts may fail
when
run in parallel
(most notably F<ext/IO/t/io_dir.t>). If necessary, run just the failing
scripts again sequentially and see
if
the failures go away.
=head2 Running tests by hand
You can run part of the test suite by hand by using one of the
following commands from the F<t/> directory:
./perl -I../lib TEST list-of-.t-files
or
./perl -I../lib harness list-of-.t-files
(If you don't specify test scripts, the whole test suite will be run.)
=head2 Using F<t/harness>
for
testing
If you
use
C<harness>
for
testing, you have several command line
options available to you. The arguments are as follows, and are in the
order that they must appear
if
used together.
harness -v -torture -re=pattern LIST OF FILES TO TEST
harness -v -torture -re LIST OF PATTERNS TO MATCH
If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
the manifest. The file list may include shell wildcards which will be
expanded out.
=over 4
=item * -v
Run the tests under verbose mode so you can see what tests were run,
and debug output.
=item * -torture
Run the torture tests as well as the normal set.
=item * -re=PATTERN
Filter the file list so that all the test files run match PATTERN. Note
that this form is distinct from the B<-re LIST OF PATTERNS> form below
in that it allows the file list to be provided as well.
=item * -re LIST OF PATTERNS
Filter the file list so that all the test files run match
/(LIST|OF|PATTERNS)/. Note that
with
this form the patterns are joined
by
'|'
and you cannot supply a list of files, instead the test files
are obtained from the MANIFEST.
=back
You can run an individual test by a command similar to
./perl -I../lib path/to/foo.t
except that the harnesses set up some environment variables that may
affect the execution of the test:
=over 4
=item * PERL_CORE=1
indicates that we're running this test as part of the perl core test
suite. This is useful
for
modules that have a dual life on CPAN.
=item * PERL_DESTRUCT_LEVEL=2
is set to 2
if
it isn't set already (see
L<perlhacktips/PERL_DESTRUCT_LEVEL>).
=item * PERL
(used only by F<t/TEST>)
if
set, overrides the path to the perl
executable that should be used to run the tests (the
default
being
F<./perl>).
=item * PERL_SKIP_TTY_TEST
if
set, tells to skip the tests that need a terminal. It's actually set
automatically by the Makefile, but can also be forced artificially by
running
'make test_notty'
.
=back
=head3 Other environment variables that may influence tests
=over 4
=item * PERL_TEST_Net_Ping
Setting this variable runs all the Net::Ping modules tests, otherwise
some tests that interact
with
the outside world are skipped. See
L<perl58delta>.
=item * PERL_TEST_NOVREXX
Setting this variable skips the vrexx.t tests
for
OS2::REXX.
=item * PERL_TEST_NUMCONVERTS
This sets a variable in op/numconvert.t.
=back
See also the documentation
for
the Test and Test::Harness modules,
for
more environment variables that affect testing.
=head1 MORE READING FOR GUTS HACKERS
To hack on the Perl guts, you'll need to
read
the following things:
=over 4
=item * L<perlsource>
An overview of the Perl source tree. This will help you find the files
you're looking
for
.
=item * L<perlinterp>
An overview of the Perl interpreter source code and some details on how
Perl does what it does.
=item * L<perlhacktut>
This document walks through the creation of a small patch to Perl's C
code. If you're just getting started
with
Perl core hacking, this will
help you understand how it works.
=item * L<perlhacktips>
More details on hacking the Perl core. This document focuses on lower
level details such as how to
write
tests, compilation issues,
portability, debugging, etc.
If you plan on doing serious C hacking, make sure to
read
this.
=item * L<perlguts>
This is of paramount importance, since it's the documentation of what
goes where in the Perl source. Read it over a couple of
times
and it
might start to make sense - don
't worry if it doesn'
t yet, because the
best way to
study
it is to
read
it in conjunction
with
poking at Perl
source, and we'll
do
that later on.
Gisle Aas's
"illustrated perlguts"
, also known as I<illguts>,
has
very
helpful pictures:
=item * L<perlxstut> and L<perlxs>
A working knowledge of XSUB programming is incredibly useful
for
core
hacking; XSUBs
use
techniques drawn from the PP code, the portion of
the guts that actually executes a Perl program. It's a lot gentler to
learn those techniques from simple examples and explanation than from
the core itself.
=item * L<perlapi>
The documentation
for
the Perl API explains what some of the internal
functions
do
, as well as the many macros used in the source.
=item * F<Porting/pumpkin.pod>
This is a collection of words of wisdom
for
a Perl porter; some of it
is only useful to the pumpkin holder, but most of it applies to anyone
wanting to go about Perl development.
=item * The perl5-porters FAQ
This should be available from
reading perl5-porters, information on how perl5-porters works and how
Perl development in general works.
=back
=head1 CPAN TESTERS AND PERL SMOKERS
who test CPAN modules on a variety of platforms.
automatically test Perl source releases on platforms
with
various
configurations.
Both efforts welcome volunteers. In order to get involved in smoke
testing of the perl itself visit
testing CPAN modules visit
=head1 WHAT NEXT?
If you've
read
all the documentation in the document and the ones
listed above, you're more than ready to hack on Perl.
Here's some more recommendations
=over 4
=item *
Subscribe to perl5-porters, follow the patches and
try
and understand
them; don
't be afraid to ask if there'
s a portion you're not clear on -
who knows, you may unearth a bug in the patch...
=item *
Do
read
the README associated
with
your operating
system
, e.g.
README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
README
if
you find anything missing or changed over a new OS release.
=item *
Find an area of Perl that seems interesting to you, and see
if
you can
work out how it works. Scan through the source, and step over it in the
debugger. Play, poke, investigate, fiddle! You'll probably get to
understand not just your chosen area but a much wider range of
F<perl>
's activity as well, and probably sooner than you'
d think.
=back
=head2
"The Road goes ever on and on, down from the door where it began."
If you can
do
these things, you've started on the long road to Perl
porting. Thanks
for
wanting to help make Perl better - and happy
hacking!
=head2 Metaphoric Quotations
If you recognized the quote about the Road above, you're in luck.
Most software projects begin
each
file
with
a literal description of
each
file's purpose. Perl instead begins
each
with
a literary allusion
to that file's purpose.
Like chapters in many books, all top-level Perl source files (along
with
a few others here and there) begin
with
an epigrammatic
inscription that alludes, indirectly and metaphorically, to the
material you're about to
read
.
Quotations are taken from writings of J.R.R. Tolkien pertaining to his
Legendarium, almost always from I<The Lord of the Rings>. Chapters and
page numbers are
given
using the following editions:
=over 4
=item *
I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
edition of 2007 was used, published in the UK by Harper Collins
Publishers and in the US by the Houghton Mifflin Company.
=item *
I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
50th-anniversary edition of 2004 was used, published in the UK by
Harper Collins Publishers and in the US by the Houghton Mifflin
Company.
=item *
I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
12 volumes in Christopher's mammoth I<History of Middle Earth>. Page
numbers derive from the hardcover edition, first published in 1983 by
George Allen & Unwin;
no
page numbers changed
for
the special 3-volume
omnibus edition of 2002 or the various trade-paper editions, all again
now by Harper Collins or Houghton Mifflin.
=back
Other JRRT books fair game
for
quotes would thus include I<The
Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
and I<The Tale of the Children of Hurin>, all but the first
posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
perfectly fine and probably best to quote from, provided you can find a
suitable quote there.
So
if
you were to supply a new, complete, top-level source file to add
to Perl, you should conform to this peculiar practice by yourself
selecting an appropriate quotation from Tolkien, retaining the original
spelling and punctuation and using the same
format
the rest of the
quotes are in. Indirect and oblique is just fine; remember, it's a
metaphor, so being meta is,
after
all, what it's
for
.
=head1 AUTHOR
This document was originally written by Nathan Torkington, and is
maintained by the perl5-porters mailing list.