4 Consistent formatting of this file is achieved with:
5 perl ./Porting/podtidy pod/perlhack.pod
9 perlhack - How to hack on Perl
13 This document explains how Perl development works. It includes details
14 about the Perl 5 Porters email list, the Perl repository, the Perlbug
15 bug tracker, patch guidelines, and commentary on Perl development
18 =head1 SUPER QUICK PATCH GUIDE
20 If you just want to submit a single small patch like a pod fix, a test
21 for a bug, comment fixes, etc., it's easy! Here's how:
25 =item * Check out the source repository
27 The perl source is in a git repository. You can clone the repository
28 with the following command:
30 % git clone git://perl5.git.perl.org/perl.git perl
32 =item * Make your change
36 =item * Test your change
38 You can run all the tests with the following commands:
40 % ./Configure -des -Dusedevel
43 Keep hacking until the tests pass.
45 =item * Commit your change
47 Committing your work will save the change I<on your local system>:
49 % git commit -a -m 'Commit message goes here'
51 Make sure the commit message describes your change in a single
52 sentence. For example, "Fixed spelling errors in perlhack.pod".
54 =item * Send your change to perlbug
56 The next step is to submit your patch to the Perl core ticket system
59 Assuming your patch consists of a single git commit, the following
60 writes the file as a MIME attachment, and sends it with a meaningful
63 % git format-patch -1 --attach
64 % perlbug -s "[PATCH] $(git log -1 --oneline HEAD)" -f 0001-*.patch
66 The perlbug program will ask you a few questions about your email
67 address and the patch you're submitting. Once you've answered them you
68 can submit your patch.
72 The porters appreciate the time you spent helping to make Perl better.
79 If you want to report a bug in Perl, you must use the F<perlbug> command
80 line tool. This tool will ensure that your bug report includes all the
81 relevant system and configuration information.
83 To browse existing Perl bugs and patches, you can use the web interface
84 at L<http://rt.perl.org/>.
86 Please check the archive of the perl5-porters list (see below) and/or
87 the bug tracking system before submitting a bug report. Often, you'll
88 find that the bug has been reported already.
90 You can log in to the bug tracking system and comment on existing bug
91 reports. If you have additional information regarding an existing bug,
92 please add it. This will help the porters fix the bug.
96 The perl5-porters (p5p) mailing list is where the Perl standard
97 distribution is maintained and developed. The people who maintain Perl
98 are also referred to as the "Perl 5 Porters", "p5p" or just the "porters".
100 A searchable archive of the list is available at
101 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/>. There is
102 also another archive at
103 L<http://archive.develooper.com/perl5-porters@perl.org/>.
105 =head2 perl-changes mailing list
107 The perl5-changes mailing list receives a copy of each patch that gets
108 submitted to the maintenance and development branches of the perl
109 repository. See L<http://lists.perl.org/list/perl5-changes.html> for
110 subscription and archive information.
112 =head1 GETTING THE PERL SOURCE
114 All of Perl's source code is kept centrally in a Git repository at
115 I<perl5.git.perl.org>. The repository contains many Perl revisions from
116 Perl 1 onwards and all the revisions from Perforce, the previous
117 version control system.
119 For much more detail on using git with the Perl repository, please see
122 =head2 Read access via Git
124 You will need a copy of Git for your computer. You can fetch a copy of
125 the repository using the git protocol:
127 % git clone git://perl5.git.perl.org/perl.git perl
129 This clones the repository and makes a local copy in the F<perl>
132 If you cannot use the git protocol for firewall reasons, you can also
133 clone via http, though this is much slower:
135 % git clone http://perl5.git.perl.org/perl.git perl
137 =head2 Read access via the web
139 You may access the repository over the web. This allows you to browse
140 the tree, see recent commits, subscribe to RSS feeds for the changes,
141 search for particular commits and more. You may access it at
142 L<http://perl5.git.perl.org/perl.git>. A mirror of the repository is
143 found at L<http://github.com/mirrors/perl>.
145 =head2 Read access via rsync
147 You can also choose to use rsync to get a copy of the current source
148 tree for the bleadperl branch and all maintenance branches:
150 % rsync -avz rsync://perl5.git.perl.org/perl-current .
151 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
152 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
153 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
154 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
155 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
157 (Add the C<--delete> option to remove leftover files.)
159 To get a full list of the available sync points:
161 % rsync perl5.git.perl.org::
163 =head2 Write access via git
165 If you have a commit bit, please see L<perlgit> for more details on
170 If you're planning to do more extensive work than a single small fix,
171 we encourage you to read the documentation below. This will help you
172 focus your work and make your patches easier to incorporate into the
175 =head2 Submitting patches
177 If you have a small patch to submit, please submit it via perlbug. You
178 can also send email directly to perlbug@perl.org. Please note that
179 messages sent to perlbug may be held in a moderation queue, so you
180 won't receive a response immediately.
182 You'll know your submission has been processed when you receive an
183 email from our ticket tracking system. This email will give you a
184 ticket number. Once your patch has made it to the ticket tracking
185 system, it will also be sent to the perl5-porters@perl.org list.
187 Patches are reviewed and discussed on the p5p list. Simple,
188 uncontroversial patches will usually be applied without any discussion.
189 When the patch is applied, the ticket will be updated and you will
190 receive email. In addition, an email will be sent to the p5p list.
192 In other cases, the patch will need more work or discussion. That will
193 happen on the p5p list.
195 You are encouraged to participate in the discussion and advocate for
196 your patch. Sometimes your patch may get lost in the shuffle. It's
197 appropriate to send a reminder email to p5p if no action has been taken
198 in a month. Please remember that the Perl 5 developers are all
199 volunteers, and be polite.
201 Changes are always applied directly to the main development branch,
202 called "blead". Some patches may be backported to a maintenance branch.
203 If you think your patch is appropriate for the maintenance branch,
204 please explain why when you submit it.
206 =head2 Getting your patch accepted
208 If you are submitting a code patch there are several things that you
209 can do to help the Perl 5 Porters accept your patch.
213 If you used git to check out the Perl source, then using C<git
214 format-patch> will produce a patch in a style suitable for Perl. The
215 C<format-patch> command produces one patch file for each commit you
216 made. If you prefer to send a single patch for all commits, you can use
221 % git diff blead my-branch-name
223 This produces a patch based on the difference between blead and your
224 current branch. It's important to make sure that blead is up to date
225 before producing the diff, that's why we call C<git pull> first.
227 We strongly recommend that you use git if possible. It will make your
228 life easier, and ours as well.
230 However, if you're not using git, you can still produce a suitable
231 patch. You'll need a pristine copy of the Perl source to diff against.
232 The porters prefer unified diffs. Using GNU C<diff>, you can produce a
235 % diff -Npurd perl.pristine perl.mine
237 Make sure that you C<make realclean> in your copy of Perl to remove any
238 build artifacts, or you may get a confusing result.
240 =head3 Commit message
242 As you craft each patch you intend to submit to the Perl core, it's
243 important to write a good commit message. This is especially important
244 if your submission will consist of a series of commits.
246 The first line of the commit message should be a short description
247 without a period. It should be no longer than the subject line of an
248 email, 50 characters being a good rule of thumb.
250 A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
251 only display the first line (cut off at 50 characters) when presenting
254 The commit message should include a description of the problem that the
255 patch corrects or new functionality that the patch adds.
257 As a general rule of thumb, your commit message should help a
258 programmer who knows the Perl core quickly understand what you were
259 trying to do, how you were trying to do it, and why the change matters
266 Your commit message should describe why the change you are making is
267 important. When someone looks at your change in six months or six
268 years, your intent should be clear.
270 If you're deprecating a feature with the intent of later simplifying
271 another bit of code, say so. If you're fixing a performance problem or
272 adding a new feature to support some other bit of the core, mention
277 Your commit message should describe what part of the Perl core you're
278 changing and what you expect your patch to do.
282 While it's not necessary for documentation changes, new tests or
283 trivial patches, it's often worth explaining how your change works.
284 Even if it's clear to you today, it may not be clear to a porter next
289 A commit message isn't intended to take the place of comments in your
290 code. Commit messages should describe the change you made, while code
291 comments should describe the current state of the code.
293 If you've just implemented a new feature, complete with doc, tests and
294 well-commented code, a brief commit message will often suffice. If,
295 however, you've just changed a single character deep in the parser or
296 lexer, you might need to write a small novel to ensure that future
297 readers understand what you did and why you did it.
299 =head3 Comments, Comments, Comments
301 Be sure to adequately comment your code. While commenting every line is
302 unnecessary, anything that takes advantage of side effects of
303 operators, that creates changes that will be felt outside of the
304 function being patched, or that others may find confusing should be
305 documented. If you are going to err, it is better to err on the side of
306 adding too many comments than too few.
308 The best comments explain I<why> the code does what it does, not I<what
313 In general, please follow the particular style of the code you are
316 In particular, follow these general guidelines for patching Perl
323 8-wide tabs (no exceptions!)
327 4-wide indents for code, 2-wide indents for nested CPP #defines
331 Try hard not to exceed 79-columns
339 Uncuddled elses and "K&R" style for indenting control constructs
343 No C++ style (//) comments
347 Mark places that need to be revisited with XXX (and revisit often!)
351 Opening brace lines up with "if" when conditional spans multiple lines;
352 should be at end-of-line otherwise
356 In function definitions, name starts in column 0 (return value is on
361 Single space after keywords that are followed by parens, no space
362 between function name and following paren
366 Avoid assignments in conditionals, but if they're unavoidable, use
367 extra paren, e.g. "if (a && (b = c)) ..."
371 "return foo;" rather than "return(foo);"
375 "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
381 If your patch changes code (rather than just changing documentation),
382 you should also include one or more test cases which illustrate the bug
383 you're fixing or validate the new functionality you're adding. In
384 general, you should update an existing test file rather than create a
387 Your test suite additions should generally follow these guidelines
388 (courtesy of Gurusamy Sarathy <gsar@activestate.com>):
394 Know what you're testing. Read the docs, and the source.
398 Tend to fail, not succeed.
402 Interpret results strictly.
406 Use unrelated features (this will flush out bizarre interactions).
410 Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
414 Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
415 found in t/op/tie.t is much more maintainable, and gives better failure
420 Give meaningful error messages when a test fails.
424 Avoid using qx// and system() unless you are testing for them. If you
425 do use them, make sure that you cover _all_ perl platforms.
429 Unlink any temporary files you create.
433 Promote unforeseen warnings to errors with $SIG{__WARN__}.
437 Be sure to use the libraries and modules shipped with the version being
438 tested, not those that were already installed.
442 Add comments to the code explaining what you are testing for.
446 Make updating the '1..42' string unnecessary. Or make sure that you
451 Test _all_ behaviors of a given operator, library, or function.
453 Test all optional arguments.
455 Test return values in various contexts (boolean, scalar, list, lvalue).
457 Use both global and lexical variables.
459 Don't forget the exceptional, pathological cases.
463 =head2 Patching a core module
465 This works just like patching anything else, with one extra
468 Modules in the F<cpan/> directory of the source tree are maintained
469 outside of the Perl core. When the author updates the module, the
470 updates are simply copied into the core. See that module's
471 documentation or its listing on L<http://search.cpan.org/> for more
472 information on reporting bugs and submitting patches.
474 In most cases, patches to modules in F<cpan/> should be sent upstream
475 and should not be applied to the Perl core individually. If a patch
476 to a file in F<cpan/> absolutely cannot wait for the fix to be made
477 upstream, released to CPAN and copied to blead, you must add (or
478 update) a C<CUSTOMIZED> entry in the F<"Porting/Maintainers.pl"> file
479 to flag that a local modification has been made. See
480 F<"Porting/Maintainers.pl"> for more details.
482 In contrast, modules in the F<dist/> directory are maintained in the
485 =head2 Updating perldelta
487 For changes significant enough to warrant a F<pod/perldelta.pod> entry,
488 the porters will greatly appreciate it if you submit a delta entry
489 along with your actual change. Significant changes include, but are not
496 Adding, deprecating, or removing core features
500 Adding, deprecating, removing, or upgrading core or dual-life modules
504 Adding new core tests
508 Fixing security issues and user-visible bugs in the core
512 Changes that might break existing code, either on the perl or C level
516 Significant performance improvements
520 Adding, removing, or significantly changing documentation in the
525 Important platform-specific changes
529 Please make sure you add the perldelta entry to the right section
530 within F<pod/perldelta.pod>. More information on how to write good
531 perldelta entries is available in the C<Style> section of
532 F<Porting/how_to_write_a_perldelta.pod>.
534 =head2 What makes for a good patch?
536 New features and extensions to the language can be contentious. There
537 is no specific set of criteria which determine what features get added,
538 but here are some questions to consider when developing a patch:
540 =head3 Does the concept match the general goals of Perl?
542 Our goals include, but are not limited to:
548 Keep it fast, simple, and useful.
552 Keep features/concepts as orthogonal as possible.
556 No arbitrary limits (platforms, data sizes, cultures).
560 Keep it open and exciting to use/patch/advocate Perl everywhere.
564 Either assimilate new technologies, or build bridges to them.
568 =head3 Where is the implementation?
570 All the talk in the world is useless without an implementation. In
571 almost every case, the person or people who argue for a new feature
572 will be expected to be the ones who implement it. Porters capable of
573 coding new features have their own agendas, and are not available to
574 implement your (possibly good) idea.
576 =head3 Backwards compatibility
578 It's a cardinal sin to break existing Perl programs. New warnings can
579 be contentious--some say that a program that emits warnings is not
580 broken, while others say it is. Adding keywords has the potential to
581 break programs, changing the meaning of existing token sequences or
582 functions might break programs.
584 The Perl 5 core includes mechanisms to help porters make backwards
585 incompatible changes more compatible such as the L<feature> and
586 L<deprecate> modules. Please use them when appropriate.
588 =head3 Could it be a module instead?
590 Perl 5 has extension mechanisms, modules and XS, specifically to avoid
591 the need to keep changing the Perl interpreter. You can write modules
592 that export functions, you can give those functions prototypes so they
593 can be called like built-in functions, you can even write XS code to
594 mess with the runtime data structures of the Perl interpreter if you
595 want to implement really complicated things.
597 Whenever possible, new features should be prototyped in a CPAN module
598 before they will be considered for the core.
600 =head3 Is the feature generic enough?
602 Is this something that only the submitter wants added to the language,
603 or is it broadly useful? Sometimes, instead of adding a feature with a
604 tight focus, the porters might decide to wait until someone implements
605 the more generalized feature.
607 =head3 Does it potentially introduce new bugs?
609 Radical rewrites of large chunks of the Perl interpreter have the
610 potential to introduce new bugs.
612 =head3 How big is it?
614 The smaller and more localized the change, the better. Similarly, a
615 series of small patches is greatly preferred over a single large patch.
617 =head3 Does it preclude other desirable features?
619 A patch is likely to be rejected if it closes off future avenues of
620 development. For instance, a patch that placed a true and final
621 interpretation on prototypes is likely to be rejected because there are
622 still options for the future of prototypes that haven't been addressed.
624 =head3 Is the implementation robust?
626 Good patches (tight code, complete, correct) stand more chance of going
627 in. Sloppy or incorrect patches might be placed on the back burner
628 until the pumpking has time to fix, or might be discarded altogether
629 without further notice.
631 =head3 Is the implementation generic enough to be portable?
633 The worst patches make use of system-specific features. It's highly
634 unlikely that non-portable additions to the Perl language will be
637 =head3 Is the implementation tested?
639 Patches which change behaviour (fixing bugs or introducing new
640 features) must include regression tests to verify that everything works
643 Without tests provided by the original author, how can anyone else
644 changing perl in the future be sure that they haven't unwittingly
645 broken the behaviour the patch implements? And without tests, how can
646 the patch's author be confident that his/her hard work put into the
647 patch won't be accidentally thrown away by someone in the future?
649 =head3 Is there enough documentation?
651 Patches without documentation are probably ill-thought out or
652 incomplete. No features can be added or changed without documentation,
653 so submitting a patch for the appropriate pod docs as well as the
654 source code is important.
656 =head3 Is there another way to do it?
658 Larry said "Although the Perl Slogan is I<There's More Than One Way to
659 Do It>, I hesitate to make 10 ways to do something". This is a tricky
660 heuristic to navigate, though--one man's essential addition is another
661 man's pointless cruft.
663 =head3 Does it create too much work?
665 Work for the pumpking, work for Perl programmers, work for module
666 authors, ... Perl is supposed to be easy.
668 =head3 Patches speak louder than words
670 Working code is always preferred to pie-in-the-sky ideas. A patch to
671 add a feature stands a much higher chance of making it to the language
672 than does a random feature request, no matter how fervently argued the
673 request might be. This ties into "Will it be useful?", as the fact that
674 someone took the time to make the patch demonstrates a strong desire
679 The core uses the same testing style as the rest of Perl, a simple
680 "ok/not ok" run through Test::Harness, but there are a few special
683 There are three ways to write a test in the core. L<Test::More>,
684 F<t/test.pl> and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The
685 decision of which to use depends on what part of the test suite you're
686 working on. This is a measure to prevent a high-level failure (such as
687 Config.pm breaking) from causing basic functionality tests to fail.
689 The F<t/test.pl> library provides some of the features of
690 L<Test::More>, but avoids loading most modules and uses as few core
691 features as possible.
693 If you write your own test, use the L<Test Anything Protocol|http://testanything.org>.
697 =item * F<t/base> and F<t/comp>
699 Since we don't know if require works, or even subroutines, use ad hoc
700 tests for these two. Step carefully to avoid using the feature being
703 =item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
705 Now that basic require() and subroutines are tested, you can use the
706 F<t/test.pl> library.
708 You can also use certain libraries like Config conditionally, but be
709 sure to skip the test gracefully if it's not there.
711 =item * Everything else
713 Now that the core of Perl is tested, L<Test::More> can and should be
714 used. You can also use the full suite of core modules in the tests.
718 When you say "make test", Perl uses the F<t/TEST> program to run the
719 test suite (except under Win32 where it uses F<t/harness> instead). All
720 tests are run from the F<t/> directory, B<not> the directory which
721 contains the test. This causes some problems with the tests in F<lib/>,
722 so here's some opportunity for some patching.
724 You must be triply conscious of cross-platform concerns. This usually
725 boils down to using L<File::Spec> and avoiding things like C<fork()>
726 and C<system()> unless absolutely necessary.
728 =head2 Special C<make test> targets
730 There are various special make targets that can be used to test Perl
731 slightly differently than the standard "test" target. Not all them are
732 expected to give a 100% success rate. Many of them have several
733 aliases, and many of them are not available on certain operating
740 This runs some basic sanity tests on the source tree and helps catch
741 basic errors before you submit a patch.
745 Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests).
747 (Not available on Win32)
751 Run all the tests through L<B::Deparse>. Not all tests will succeed.
753 (Not available on Win32)
755 =item * test.taintwarn
757 Run all tests with the B<-t> command-line switch. Not all tests are
758 expected to succeed (until they're specifically fixed, of course).
760 (Not available on Win32)
764 Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
765 F<t/op>, F<t/uni> and F<t/mro> tests.
767 =item * test.valgrind check.valgrind utest.valgrind ucheck.valgrind
769 (Only in Linux) Run all the tests using the memory leak + naughty
770 memory access tool "valgrind". The log files will be named
771 F<testname.valgrind>.
773 =item * test.torture torturetest
775 Run all the usual tests and some extra tests. As of Perl 5.8.0, the only
776 extra tests are Abigail's JAPHs, F<t/japh/abigail.t>.
778 You can also run the torture test with F<t/harness> by giving
779 C<-torture> argument to F<t/harness>.
781 =item * utest ucheck test.utf8 check.utf8
783 Run all the tests with -Mutf8. Not all tests will succeed.
785 (Not available on Win32)
787 =item * minitest.utf16 test.utf16
789 Runs the tests with UTF-16 encoded scripts, encoded with different
790 versions of this encoding.
792 C<make utest.utf16> runs the test suite with a combination of C<-utf8>
793 and C<-utf16> arguments to F<t/TEST>.
795 (Not available on Win32)
799 Run the test suite with the F<t/harness> controlling program, instead
800 of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
801 L<Test::Harness> module, thus using this test target supposes that perl
802 mostly works. The main advantage for our purposes is that it prints a
803 detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it
804 doesn't redirect stderr to stdout.
806 Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
807 so there is no special "test_harness" target.
809 Under Win32's "test" target you may use the TEST_SWITCHES and
810 TEST_FILES environment variables to control the behaviour of
811 F<t/harness>. This means you can say
813 nmake test TEST_FILES="op/*.t"
814 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
816 =item * test-notty test_notty
818 Sets PERL_SKIP_TTY_TEST to true before running normal test.
822 =head2 Parallel tests
824 The core distribution can now run its regression tests in parallel on
825 Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
826 in your environment to the number of tests to run in parallel, and run
827 C<make test_harness>. On a Bourne-like shell, this can be done as
829 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
831 An environment variable is used, rather than parallel make itself,
832 because L<TAP::Harness> needs to be able to schedule individual
833 non-conflicting test scripts itself, and there is no standard interface
834 to C<make> utilities to interact with their job schedulers.
836 Note that currently some test scripts may fail when run in parallel (most
837 notably F<ext/IO/t/io_dir.t>). If necessary, run just the failing scripts
838 again sequentially and see if the failures go away.
840 =head2 Running tests by hand
842 You can run part of the test suite by hand by using one of the following
843 commands from the F<t/> directory:
845 ./perl -I../lib TEST list-of-.t-files
849 ./perl -I../lib harness list-of-.t-files
851 (If you don't specify test scripts, the whole test suite will be run.)
853 =head2 Using F<t/harness> for testing
855 If you use C<harness> for testing, you have several command line options
856 available to you. The arguments are as follows, and are in the order
857 that they must appear if used together.
859 harness -v -torture -re=pattern LIST OF FILES TO TEST
860 harness -v -torture -re LIST OF PATTERNS TO MATCH
862 If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
863 the manifest. The file list may include shell wildcards which will be
870 Run the tests under verbose mode so you can see what tests were run,
875 Run the torture tests as well as the normal set.
879 Filter the file list so that all the test files run match PATTERN. Note
880 that this form is distinct from the B<-re LIST OF PATTERNS> form below
881 in that it allows the file list to be provided as well.
883 =item * -re LIST OF PATTERNS
885 Filter the file list so that all the test files run match
886 /(LIST|OF|PATTERNS)/. Note that with this form the patterns are joined
887 by '|' and you cannot supply a list of files, instead the test files
888 are obtained from the MANIFEST.
892 You can run an individual test by a command similar to
894 ./perl -I../lib path/to/foo.t
896 except that the harnesses set up some environment variables that may
897 affect the execution of the test:
903 indicates that we're running this test as part of the perl core test
904 suite. This is useful for modules that have a dual life on CPAN.
906 =item * PERL_DESTRUCT_LEVEL=2
908 is set to 2 if it isn't set already (see
909 L<perlhacktips/PERL_DESTRUCT_LEVEL>).
913 (used only by F<t/TEST>) if set, overrides the path to the perl
914 executable that should be used to run the tests (the default being
917 =item * PERL_SKIP_TTY_TEST
919 if set, tells to skip the tests that need a terminal. It's actually set
920 automatically by the Makefile, but can also be forced artificially by
921 running 'make test_notty'.
925 =head3 Other environment variables that may influence tests
929 =item * PERL_TEST_Net_Ping
931 Setting this variable runs all the Net::Ping modules tests, otherwise
932 some tests that interact with the outside world are skipped. See
935 =item * PERL_TEST_NOVREXX
937 Setting this variable skips the vrexx.t tests for OS2::REXX.
939 =item * PERL_TEST_NUMCONVERTS
941 This sets a variable in op/numconvert.t.
945 See also the documentation for the Test and Test::Harness modules, for
946 more environment variables that affect testing.
948 =head1 MORE READING FOR GUTS HACKERS
950 To hack on the Perl guts, you'll need to read the following things:
954 =item * L<perlsource>
956 An overview of the Perl source tree. This will help you find the files
959 =item * L<perlinterp>
961 An overview of the Perl interpreter source code and some details on how
962 Perl does what it does.
964 =item * L<perlhacktut>
966 This document walks through the creation of a small patch to Perl's C
967 code. If you're just getting started with Perl core hacking, this will
968 help you understand how it works.
970 =item * L<perlhacktips>
972 More details on hacking the Perl core. This document focuses on lower
973 level details such as how to write tests, compilation issues,
974 portability, debugging, etc.
976 If you plan on doing serious C hacking, make sure to read this.
980 This is of paramount importance, since it's the documentation of what
981 goes where in the Perl source. Read it over a couple of times and it
982 might start to make sense - don't worry if it doesn't yet, because the
983 best way to study it is to read it in conjunction with poking at Perl
984 source, and we'll do that later on.
986 Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very
989 L<http://search.cpan.org/dist/illguts/>
991 =item * L<perlxstut> and L<perlxs>
993 A working knowledge of XSUB programming is incredibly useful for core
994 hacking; XSUBs use techniques drawn from the PP code, the portion of
995 the guts that actually executes a Perl program. It's a lot gentler to
996 learn those techniques from simple examples and explanation than from
1001 The documentation for the Perl API explains what some of the internal
1002 functions do, as well as the many macros used in the source.
1004 =item * F<Porting/pumpkin.pod>
1006 This is a collection of words of wisdom for a Perl porter; some of it
1007 is only useful to the pumpkin holder, but most of it applies to anyone
1008 wanting to go about Perl development.
1010 =item * The perl5-porters FAQ
1012 This should be available from
1013 http://dev.perl.org/perl5/docs/p5p-faq.html . It contains hints on
1014 reading perl5-porters, information on how perl5-porters works and how
1015 Perl development in general works.
1019 =head1 CPAN TESTERS AND PERL SMOKERS
1021 The CPAN testers ( http://testers.cpan.org/ ) are a group of volunteers
1022 who test CPAN modules on a variety of platforms.
1024 Perl Smokers ( http://www.nntp.perl.org/group/perl.daily-build/ and
1025 http://www.nntp.perl.org/group/perl.daily-build.reports/ )
1026 automatically test Perl source releases on platforms with various
1029 Both efforts welcome volunteers. In order to get involved in smoke
1030 testing of the perl itself visit
1031 L<http://search.cpan.org/dist/Test-Smoke/>. In order to start smoke
1032 testing CPAN modules visit
1033 L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> or
1034 L<http://search.cpan.org/dist/minismokebox/> or
1035 L<http://search.cpan.org/dist/CPAN-Reporter/>.
1039 If you've read all the documentation in the document and the ones
1040 listed above, you're more than ready to hack on Perl.
1042 Here's some more recommendations
1048 Subscribe to perl5-porters, follow the patches and try and understand
1049 them; don't be afraid to ask if there's a portion you're not clear on -
1050 who knows, you may unearth a bug in the patch...
1054 Do read the README associated with your operating system, e.g.
1055 README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
1056 README if you find anything missing or changed over a new OS release.
1060 Find an area of Perl that seems interesting to you, and see if you can
1061 work out how it works. Scan through the source, and step over it in the
1062 debugger. Play, poke, investigate, fiddle! You'll probably get to
1063 understand not just your chosen area but a much wider range of
1064 F<perl>'s activity as well, and probably sooner than you'd think.
1068 =head2 "The Road goes ever on and on, down from the door where it began."
1070 If you can do these things, you've started on the long road to Perl
1071 porting. Thanks for wanting to help make Perl better - and happy
1074 =head2 Metaphoric Quotations
1076 If you recognized the quote about the Road above, you're in luck.
1078 Most software projects begin each file with a literal description of
1079 each file's purpose. Perl instead begins each with a literary allusion
1080 to that file's purpose.
1082 Like chapters in many books, all top-level Perl source files (along
1083 with a few others here and there) begin with an epigrammatic inscription
1084 that alludes, indirectly and metaphorically, to the material you're
1087 Quotations are taken from writings of J.R.R. Tolkien pertaining to his
1088 Legendarium, almost always from I<The Lord of the Rings>. Chapters and
1089 page numbers are given using the following editions:
1095 I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
1096 edition of 2007 was used, published in the UK by Harper Collins
1097 Publishers and in the US by the Houghton Mifflin Company.
1101 I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
1102 50th-anniversary edition of 2004 was used, published in the UK by
1103 Harper Collins Publishers and in the US by the Houghton Mifflin
1108 I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
1109 by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
1110 12 volumes in Christopher's mammoth I<History of Middle Earth>. Page
1111 numbers derive from the hardcover edition, first published in 1983 by
1112 George Allen & Unwin; no page numbers changed for the special 3-volume
1113 omnibus edition of 2002 or the various trade-paper editions, all again
1114 now by Harper Collins or Houghton Mifflin.
1118 Other JRRT books fair game for quotes would thus include I<The
1119 Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
1120 and I<The Tale of the Children of Hurin>, all but the first
1121 posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
1122 perfectly fine and probably best to quote from, provided you can find a
1123 suitable quote there.
1125 So if you were to supply a new, complete, top-level source file to add
1126 to Perl, you should conform to this peculiar practice by yourself
1127 selecting an appropriate quotation from Tolkien, retaining the original
1128 spelling and punctuation and using the same format the rest of the
1129 quotes are in. Indirect and oblique is just fine; remember, it's a
1130 metaphor, so being meta is, after all, what it's for.
1134 This document was originally written by Nathan Torkington, and is
1135 maintained by the perl5-porters mailing list.