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 * Ensure you're following the latest advice
34 In case the advice in this guide has been updated recently, read the
35 latest version directly from the perl source:
37 % perldoc pod/perlhack.pod
39 =item * Make your change
43 =item * Test your change
45 You can run all the tests with the following commands:
47 % ./Configure -des -Dusedevel
50 Keep hacking until the tests pass.
52 =item * Commit your change
54 Committing your work will save the change I<on your local system>:
56 % git commit -a -m 'Commit message goes here'
58 Make sure the commit message describes your change in a single
59 sentence. For example, "Fixed spelling errors in perlhack.pod".
61 =item * Send your change to perlbug
63 The next step is to submit your patch to the Perl core ticket system
66 If your changes are in a single git commit, run the following commands
67 to generate the patch file and attach it to your bug report:
70 % ./perl -Ilib utils/perlbug -p 0001-*.patch
72 The perlbug program will ask you a few questions about your email
73 address and the patch you're submitting. Once you've answered them it
74 will submit your patch via email.
76 If your changes are in multiple commits, generate a patch file for each
77 one and provide them to perlbug's C<-p> option separated by commas:
80 % ./perl -Ilib utils/perlbug -p 0001-fix1.patch,0002-fix2.patch,\
83 When prompted, pick a subject that summarizes your changes.
87 The porters appreciate the time you spent helping to make Perl better.
92 The next time you wish to make a patch, you need to start from the
93 latest perl in a pristine state. Check you don't have any local changes
94 or added files in your perl check-out which you wish to keep, then run
98 % git reset --hard origin/blead
105 If you want to report a bug in Perl, you must use the F<perlbug>
106 command line tool. This tool will ensure that your bug report includes
107 all the relevant system and configuration information.
109 To browse existing Perl bugs and patches, you can use the web interface
110 at L<http://rt.perl.org/>.
112 Please check the archive of the perl5-porters list (see below) and/or
113 the bug tracking system before submitting a bug report. Often, you'll
114 find that the bug has been reported already.
116 You can log in to the bug tracking system and comment on existing bug
117 reports. If you have additional information regarding an existing bug,
118 please add it. This will help the porters fix the bug.
120 =head1 PERL 5 PORTERS
122 The perl5-porters (p5p) mailing list is where the Perl standard
123 distribution is maintained and developed. The people who maintain Perl
124 are also referred to as the "Perl 5 Porters", "p5p" or just the
127 A searchable archive of the list is available at
128 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/>. There is
129 also another archive at
130 L<http://archive.develooper.com/perl5-porters@perl.org/>.
132 =head2 perl-changes mailing list
134 The perl5-changes mailing list receives a copy of each patch that gets
135 submitted to the maintenance and development branches of the perl
136 repository. See L<http://lists.perl.org/list/perl5-changes.html> for
137 subscription and archive information.
141 Many porters are also active on the L<irc://irc.perl.org/#p5p> channel.
142 Feel free to join the channel and ask questions about hacking on the
145 =head1 GETTING THE PERL SOURCE
147 All of Perl's source code is kept centrally in a Git repository at
148 I<perl5.git.perl.org>. The repository contains many Perl revisions
149 from Perl 1 onwards and all the revisions from Perforce, the previous
150 version control system.
152 For much more detail on using git with the Perl repository, please see
155 =head2 Read access via Git
157 You will need a copy of Git for your computer. You can fetch a copy of
158 the repository using the git protocol:
160 % git clone git://perl5.git.perl.org/perl.git perl
162 This clones the repository and makes a local copy in the F<perl>
165 If you cannot use the git protocol for firewall reasons, you can also
166 clone via http, though this is much slower:
168 % git clone http://perl5.git.perl.org/perl.git perl
170 =head2 Read access via the web
172 You may access the repository over the web. This allows you to browse
173 the tree, see recent commits, subscribe to RSS feeds for the changes,
174 search for particular commits and more. You may access it at
175 L<http://perl5.git.perl.org/perl.git>. A mirror of the repository is
176 found at L<https://github.com/Perl/perl5>.
178 =head2 Read access via rsync
180 You can also choose to use rsync to get a copy of the current source
181 tree for the bleadperl branch and all maintenance branches:
183 % rsync -avz rsync://perl5.git.perl.org/perl-current .
184 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
185 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
186 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
187 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
188 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
190 (Add the C<--delete> option to remove leftover files.)
192 To get a full list of the available sync points:
194 % rsync perl5.git.perl.org::
196 =head2 Write access via git
198 If you have a commit bit, please see L<perlgit> for more details on
203 If you're planning to do more extensive work than a single small fix,
204 we encourage you to read the documentation below. This will help you
205 focus your work and make your patches easier to incorporate into the
208 =head2 Submitting patches
210 If you have a small patch to submit, please submit it via perlbug. You
211 can also send email directly to perlbug@perl.org. Please note that
212 messages sent to perlbug may be held in a moderation queue, so you
213 won't receive a response immediately.
215 You'll know your submission has been processed when you receive an
216 email from our ticket tracking system. This email will give you a
217 ticket number. Once your patch has made it to the ticket tracking
218 system, it will also be sent to the perl5-porters@perl.org list.
220 Patches are reviewed and discussed on the p5p list. Simple,
221 uncontroversial patches will usually be applied without any discussion.
222 When the patch is applied, the ticket will be updated and you will
223 receive email. In addition, an email will be sent to the p5p list.
225 In other cases, the patch will need more work or discussion. That will
226 happen on the p5p list.
228 You are encouraged to participate in the discussion and advocate for
229 your patch. Sometimes your patch may get lost in the shuffle. It's
230 appropriate to send a reminder email to p5p if no action has been taken
231 in a month. Please remember that the Perl 5 developers are all
232 volunteers, and be polite.
234 Changes are always applied directly to the main development branch,
235 called "blead". Some patches may be backported to a maintenance
236 branch. If you think your patch is appropriate for the maintenance
237 branch (see L<perlpolicy/MAINTENANCE BRANCHES>), please explain why
240 =head2 Getting your patch accepted
242 If you are submitting a code patch there are several things that you
243 can do to help the Perl 5 Porters accept your patch.
247 If you used git to check out the Perl source, then using C<git
248 format-patch> will produce a patch in a style suitable for Perl. The
249 C<format-patch> command produces one patch file for each commit you
250 made. If you prefer to send a single patch for all commits, you can
255 % git diff blead my-branch-name
257 This produces a patch based on the difference between blead and your
258 current branch. It's important to make sure that blead is up to date
259 before producing the diff, that's why we call C<git pull> first.
261 We strongly recommend that you use git if possible. It will make your
262 life easier, and ours as well.
264 However, if you're not using git, you can still produce a suitable
265 patch. You'll need a pristine copy of the Perl source to diff against.
266 The porters prefer unified diffs. Using GNU C<diff>, you can produce a
269 % diff -Npurd perl.pristine perl.mine
271 Make sure that you C<make realclean> in your copy of Perl to remove any
272 build artifacts, or you may get a confusing result.
274 =head3 Commit message
276 As you craft each patch you intend to submit to the Perl core, it's
277 important to write a good commit message. This is especially important
278 if your submission will consist of a series of commits.
280 The first line of the commit message should be a short description
281 without a period. It should be no longer than the subject line of an
282 email, 50 characters being a good rule of thumb.
284 A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
285 only display the first line (cut off at 50 characters) when presenting
288 The commit message should include a description of the problem that the
289 patch corrects or new functionality that the patch adds.
291 As a general rule of thumb, your commit message should help a
292 programmer who knows the Perl core quickly understand what you were
293 trying to do, how you were trying to do it, and why the change matters
300 Your commit message should describe why the change you are making is
301 important. When someone looks at your change in six months or six
302 years, your intent should be clear.
304 If you're deprecating a feature with the intent of later simplifying
305 another bit of code, say so. If you're fixing a performance problem or
306 adding a new feature to support some other bit of the core, mention
311 Your commit message should describe what part of the Perl core you're
312 changing and what you expect your patch to do.
316 While it's not necessary for documentation changes, new tests or
317 trivial patches, it's often worth explaining how your change works.
318 Even if it's clear to you today, it may not be clear to a porter next
323 A commit message isn't intended to take the place of comments in your
324 code. Commit messages should describe the change you made, while code
325 comments should describe the current state of the code.
327 If you've just implemented a new feature, complete with doc, tests and
328 well-commented code, a brief commit message will often suffice. If,
329 however, you've just changed a single character deep in the parser or
330 lexer, you might need to write a small novel to ensure that future
331 readers understand what you did and why you did it.
333 =head3 Comments, Comments, Comments
335 Be sure to adequately comment your code. While commenting every line
336 is unnecessary, anything that takes advantage of side effects of
337 operators, that creates changes that will be felt outside of the
338 function being patched, or that others may find confusing should be
339 documented. If you are going to err, it is better to err on the side
340 of adding too many comments than too few.
342 The best comments explain I<why> the code does what it does, not I<what
347 In general, please follow the particular style of the code you are
350 In particular, follow these general guidelines for patching Perl
357 8-wide tabs (no exceptions!)
361 4-wide indents for code, 2-wide indents for nested CPP #defines
365 Try hard not to exceed 79-columns
373 Uncuddled elses and "K&R" style for indenting control constructs
377 No C++ style (//) comments
381 Mark places that need to be revisited with XXX (and revisit often!)
385 Opening brace lines up with "if" when conditional spans multiple lines;
386 should be at end-of-line otherwise
390 In function definitions, name starts in column 0 (return value is on
395 Single space after keywords that are followed by parens, no space
396 between function name and following paren
400 Avoid assignments in conditionals, but if they're unavoidable, use
401 extra paren, e.g. "if (a && (b = c)) ..."
405 "return foo;" rather than "return(foo);"
409 "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
413 Do not declare variables using "register". It may be counterproductive
414 with modern compilers, and is deprecated in C++, under which the Perl
415 source is regularly compiled.
419 In-line functions that are in headers that are accessible to XS code
420 need to be able to compile without warnings with commonly used extra
421 compilation flags, such as gcc's C<-Wswitch-default> which warns
422 whenever a switch statement does not have a "default" case. The use of
423 these extra flags is to catch potential problems in legal C code, and
424 is often used by Perl aggregators, such as Linux distributors.
430 If your patch changes code (rather than just changing documentation),
431 you should also include one or more test cases which illustrate the bug
432 you're fixing or validate the new functionality you're adding. In
433 general, you should update an existing test file rather than create a
436 Your test suite additions should generally follow these guidelines
437 (courtesy of Gurusamy Sarathy <gsar@activestate.com>):
443 Know what you're testing. Read the docs, and the source.
447 Tend to fail, not succeed.
451 Interpret results strictly.
455 Use unrelated features (this will flush out bizarre interactions).
459 Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
463 Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
464 found in t/op/tie.t is much more maintainable, and gives better failure
469 Give meaningful error messages when a test fails.
473 Avoid using qx// and system() unless you are testing for them. If you
474 do use them, make sure that you cover _all_ perl platforms.
478 Unlink any temporary files you create.
482 Promote unforeseen warnings to errors with $SIG{__WARN__}.
486 Be sure to use the libraries and modules shipped with the version being
487 tested, not those that were already installed.
491 Add comments to the code explaining what you are testing for.
495 Make updating the '1..42' string unnecessary. Or make sure that you
500 Test _all_ behaviors of a given operator, library, or function.
502 Test all optional arguments.
504 Test return values in various contexts (boolean, scalar, list, lvalue).
506 Use both global and lexical variables.
508 Don't forget the exceptional, pathological cases.
512 =head2 Patching a core module
514 This works just like patching anything else, with one extra
517 Modules in the F<cpan/> directory of the source tree are maintained
518 outside of the Perl core. When the author updates the module, the
519 updates are simply copied into the core. See that module's
520 documentation or its listing on L<http://search.cpan.org/> for more
521 information on reporting bugs and submitting patches.
523 In most cases, patches to modules in F<cpan/> should be sent upstream
524 and should not be applied to the Perl core individually. If a patch to
525 a file in F<cpan/> absolutely cannot wait for the fix to be made
526 upstream, released to CPAN and copied to blead, you must add (or
527 update) a C<CUSTOMIZED> entry in the F<"Porting/Maintainers.pl"> file
528 to flag that a local modification has been made. See
529 F<"Porting/Maintainers.pl"> for more details.
531 In contrast, modules in the F<dist/> directory are maintained in the
534 =head2 Updating perldelta
536 For changes significant enough to warrant a F<pod/perldelta.pod> entry,
537 the porters will greatly appreciate it if you submit a delta entry
538 along with your actual change. Significant changes include, but are
545 Adding, deprecating, or removing core features
549 Adding, deprecating, removing, or upgrading core or dual-life modules
553 Adding new core tests
557 Fixing security issues and user-visible bugs in the core
561 Changes that might break existing code, either on the perl or C level
565 Significant performance improvements
569 Adding, removing, or significantly changing documentation in the
574 Important platform-specific changes
578 Please make sure you add the perldelta entry to the right section
579 within F<pod/perldelta.pod>. More information on how to write good
580 perldelta entries is available in the C<Style> section of
581 F<Porting/how_to_write_a_perldelta.pod>.
583 =head2 What makes for a good patch?
585 New features and extensions to the language can be contentious. There
586 is no specific set of criteria which determine what features get added,
587 but here are some questions to consider when developing a patch:
589 =head3 Does the concept match the general goals of Perl?
591 Our goals include, but are not limited to:
597 Keep it fast, simple, and useful.
601 Keep features/concepts as orthogonal as possible.
605 No arbitrary limits (platforms, data sizes, cultures).
609 Keep it open and exciting to use/patch/advocate Perl everywhere.
613 Either assimilate new technologies, or build bridges to them.
617 =head3 Where is the implementation?
619 All the talk in the world is useless without an implementation. In
620 almost every case, the person or people who argue for a new feature
621 will be expected to be the ones who implement it. Porters capable of
622 coding new features have their own agendas, and are not available to
623 implement your (possibly good) idea.
625 =head3 Backwards compatibility
627 It's a cardinal sin to break existing Perl programs. New warnings can
628 be contentious--some say that a program that emits warnings is not
629 broken, while others say it is. Adding keywords has the potential to
630 break programs, changing the meaning of existing token sequences or
631 functions might break programs.
633 The Perl 5 core includes mechanisms to help porters make backwards
634 incompatible changes more compatible such as the L<feature> and
635 L<deprecate> modules. Please use them when appropriate.
637 =head3 Could it be a module instead?
639 Perl 5 has extension mechanisms, modules and XS, specifically to avoid
640 the need to keep changing the Perl interpreter. You can write modules
641 that export functions, you can give those functions prototypes so they
642 can be called like built-in functions, you can even write XS code to
643 mess with the runtime data structures of the Perl interpreter if you
644 want to implement really complicated things.
646 Whenever possible, new features should be prototyped in a CPAN module
647 before they will be considered for the core.
649 =head3 Is the feature generic enough?
651 Is this something that only the submitter wants added to the language,
652 or is it broadly useful? Sometimes, instead of adding a feature with a
653 tight focus, the porters might decide to wait until someone implements
654 the more generalized feature.
656 =head3 Does it potentially introduce new bugs?
658 Radical rewrites of large chunks of the Perl interpreter have the
659 potential to introduce new bugs.
661 =head3 How big is it?
663 The smaller and more localized the change, the better. Similarly, a
664 series of small patches is greatly preferred over a single large patch.
666 =head3 Does it preclude other desirable features?
668 A patch is likely to be rejected if it closes off future avenues of
669 development. For instance, a patch that placed a true and final
670 interpretation on prototypes is likely to be rejected because there are
671 still options for the future of prototypes that haven't been addressed.
673 =head3 Is the implementation robust?
675 Good patches (tight code, complete, correct) stand more chance of going
676 in. Sloppy or incorrect patches might be placed on the back burner
677 until the pumpking has time to fix, or might be discarded altogether
678 without further notice.
680 =head3 Is the implementation generic enough to be portable?
682 The worst patches make use of system-specific features. It's highly
683 unlikely that non-portable additions to the Perl language will be
686 =head3 Is the implementation tested?
688 Patches which change behaviour (fixing bugs or introducing new
689 features) must include regression tests to verify that everything works
692 Without tests provided by the original author, how can anyone else
693 changing perl in the future be sure that they haven't unwittingly
694 broken the behaviour the patch implements? And without tests, how can
695 the patch's author be confident that his/her hard work put into the
696 patch won't be accidentally thrown away by someone in the future?
698 =head3 Is there enough documentation?
700 Patches without documentation are probably ill-thought out or
701 incomplete. No features can be added or changed without documentation,
702 so submitting a patch for the appropriate pod docs as well as the
703 source code is important.
705 =head3 Is there another way to do it?
707 Larry said "Although the Perl Slogan is I<There's More Than One Way to
708 Do It>, I hesitate to make 10 ways to do something". This is a tricky
709 heuristic to navigate, though--one man's essential addition is another
710 man's pointless cruft.
712 =head3 Does it create too much work?
714 Work for the pumpking, work for Perl programmers, work for module
715 authors, ... Perl is supposed to be easy.
717 =head3 Patches speak louder than words
719 Working code is always preferred to pie-in-the-sky ideas. A patch to
720 add a feature stands a much higher chance of making it to the language
721 than does a random feature request, no matter how fervently argued the
722 request might be. This ties into "Will it be useful?", as the fact
723 that someone took the time to make the patch demonstrates a strong
724 desire for the feature.
728 The core uses the same testing style as the rest of Perl, a simple
729 "ok/not ok" run through Test::Harness, but there are a few special
732 There are three ways to write a test in the core: L<Test::More>,
733 F<t/test.pl> and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">.
734 The decision of which to use depends on what part of the test suite
735 you're working on. This is a measure to prevent a high-level failure
736 (such as Config.pm breaking) from causing basic functionality tests to
739 The F<t/test.pl> library provides some of the features of
740 L<Test::More>, but avoids loading most modules and uses as few core
741 features as possible.
743 If you write your own test, use the L<Test Anything
744 Protocol|http://testanything.org>.
748 =item * F<t/base>, F<t/comp> and F<t/opbasic>
750 Since we don't know if require works, or even subroutines, use ad hoc
751 tests for these three. Step carefully to avoid using the feature being
752 tested. Tests in F<t/opbasic>, for instance, have been placed there
753 rather than in F<t/op> because they test functionality which
754 F<t/test.pl> presumes has already been demonstrated to work.
756 =item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
758 Now that basic require() and subroutines are tested, you can use the
759 F<t/test.pl> library.
761 You can also use certain libraries like Config conditionally, but be
762 sure to skip the test gracefully if it's not there.
764 =item * Everything else
766 Now that the core of Perl is tested, L<Test::More> can and should be
767 used. You can also use the full suite of core modules in the tests.
771 When you say "make test", Perl uses the F<t/TEST> program to run the
772 test suite (except under Win32 where it uses F<t/harness> instead).
773 All tests are run from the F<t/> directory, B<not> the directory which
774 contains the test. This causes some problems with the tests in
775 F<lib/>, so here's some opportunity for some patching.
777 You must be triply conscious of cross-platform concerns. This usually
778 boils down to using L<File::Spec> and avoiding things like C<fork()>
779 and C<system()> unless absolutely necessary.
781 =head2 Special C<make test> targets
783 There are various special make targets that can be used to test Perl
784 slightly differently than the standard "test" target. Not all them are
785 expected to give a 100% success rate. Many of them have several
786 aliases, and many of them are not available on certain operating
793 This runs some basic sanity tests on the source tree and helps catch
794 basic errors before you submit a patch.
798 Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
799 F<t/op>, F<t/uni> and F<t/mro> tests.
801 =item * test.valgrind check.valgrind
803 (Only in Linux) Run all the tests using the memory leak + naughty
804 memory access tool "valgrind". The log files will be named
805 F<testname.valgrind>.
809 Run the test suite with the F<t/harness> controlling program, instead
810 of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
811 L<Test::Harness> module, thus using this test target supposes that perl
812 mostly works. The main advantage for our purposes is that it prints a
813 detailed summary of failed tests at the end. Also, unlike F<t/TEST>,
814 it doesn't redirect stderr to stdout.
816 Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
817 so there is no special "test_harness" target.
819 Under Win32's "test" target you may use the TEST_SWITCHES and
820 TEST_FILES environment variables to control the behaviour of
821 F<t/harness>. This means you can say
823 nmake test TEST_FILES="op/*.t"
824 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
826 =item * test-notty test_notty
828 Sets PERL_SKIP_TTY_TEST to true before running normal test.
832 =head2 Parallel tests
834 The core distribution can now run its regression tests in parallel on
835 Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
836 in your environment to the number of tests to run in parallel, and run
837 C<make test_harness>. On a Bourne-like shell, this can be done as
839 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
841 An environment variable is used, rather than parallel make itself,
842 because L<TAP::Harness> needs to be able to schedule individual
843 non-conflicting test scripts itself, and there is no standard interface
844 to C<make> utilities to interact with their job schedulers.
846 Note that currently some test scripts may fail when run in parallel
847 (most notably F<ext/IO/t/io_dir.t>). If necessary, run just the
848 failing scripts again sequentially and see if the failures go away.
850 =head2 Running tests by hand
852 You can run part of the test suite by hand by using one of the
853 following commands from the F<t/> directory:
855 ./perl -I../lib TEST list-of-.t-files
859 ./perl -I../lib harness list-of-.t-files
861 (If you don't specify test scripts, the whole test suite will be run.)
863 =head2 Using F<t/harness> for testing
865 If you use C<harness> for testing, you have several command line
866 options available to you. The arguments are as follows, and are in the
867 order that they must appear if used together.
869 harness -v -torture -re=pattern LIST OF FILES TO TEST
870 harness -v -torture -re LIST OF PATTERNS TO MATCH
872 If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
873 the manifest. The file list may include shell wildcards which will be
880 Run the tests under verbose mode so you can see what tests were run,
885 Run the torture tests as well as the normal set.
889 Filter the file list so that all the test files run match PATTERN.
890 Note that this form is distinct from the B<-re LIST OF PATTERNS> form
891 below in that it allows the file list to be provided as well.
893 =item * -re LIST OF PATTERNS
895 Filter the file list so that all the test files run match
896 /(LIST|OF|PATTERNS)/. Note that with this form the patterns are joined
897 by '|' and you cannot supply a list of files, instead the test files
898 are obtained from the MANIFEST.
902 You can run an individual test by a command similar to
904 ./perl -I../lib path/to/foo.t
906 except that the harnesses set up some environment variables that may
907 affect the execution of the test:
913 indicates that we're running this test as part of the perl core test
914 suite. This is useful for modules that have a dual life on CPAN.
916 =item * PERL_DESTRUCT_LEVEL=2
918 is set to 2 if it isn't set already (see
919 L<perlhacktips/PERL_DESTRUCT_LEVEL>).
923 (used only by F<t/TEST>) if set, overrides the path to the perl
924 executable that should be used to run the tests (the default being
927 =item * PERL_SKIP_TTY_TEST
929 if set, tells to skip the tests that need a terminal. It's actually
930 set automatically by the Makefile, but can also be forced artificially
931 by running 'make test_notty'.
935 =head3 Other environment variables that may influence tests
939 =item * PERL_TEST_Net_Ping
941 Setting this variable runs all the Net::Ping modules tests, otherwise
942 some tests that interact with the outside world are skipped. See
945 =item * PERL_TEST_NOVREXX
947 Setting this variable skips the vrexx.t tests for OS2::REXX.
949 =item * PERL_TEST_NUMCONVERTS
951 This sets a variable in op/numconvert.t.
953 =item * PERL_TEST_MEMORY
955 Setting this variable includes the tests in F<t/bigmem/>. This should
956 be set to the number of gigabytes of memory available for testing, eg.
957 C<PERL_TEST_MEMORY=4> indicates that tests that require 4GiB of
958 available memory can be run safely.
962 See also the documentation for the Test and Test::Harness modules, for
963 more environment variables that affect testing.
965 =head1 MORE READING FOR GUTS HACKERS
967 To hack on the Perl guts, you'll need to read the following things:
971 =item * L<perlsource>
973 An overview of the Perl source tree. This will help you find the files
976 =item * L<perlinterp>
978 An overview of the Perl interpreter source code and some details on how
979 Perl does what it does.
981 =item * L<perlhacktut>
983 This document walks through the creation of a small patch to Perl's C
984 code. If you're just getting started with Perl core hacking, this will
985 help you understand how it works.
987 =item * L<perlhacktips>
989 More details on hacking the Perl core. This document focuses on lower
990 level details such as how to write tests, compilation issues,
991 portability, debugging, etc.
993 If you plan on doing serious C hacking, make sure to read this.
997 This is of paramount importance, since it's the documentation of what
998 goes where in the Perl source. Read it over a couple of times and it
999 might start to make sense - don't worry if it doesn't yet, because the
1000 best way to study it is to read it in conjunction with poking at Perl
1001 source, and we'll do that later on.
1003 Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very
1006 L<http://search.cpan.org/dist/illguts/>
1008 =item * L<perlxstut> and L<perlxs>
1010 A working knowledge of XSUB programming is incredibly useful for core
1011 hacking; XSUBs use techniques drawn from the PP code, the portion of
1012 the guts that actually executes a Perl program. It's a lot gentler to
1013 learn those techniques from simple examples and explanation than from
1018 The documentation for the Perl API explains what some of the internal
1019 functions do, as well as the many macros used in the source.
1021 =item * F<Porting/pumpkin.pod>
1023 This is a collection of words of wisdom for a Perl porter; some of it
1024 is only useful to the pumpkin holder, but most of it applies to anyone
1025 wanting to go about Perl development.
1029 =head1 CPAN TESTERS AND PERL SMOKERS
1031 The CPAN testers ( http://testers.cpan.org/ ) are a group of volunteers
1032 who test CPAN modules on a variety of platforms.
1034 Perl Smokers ( http://www.nntp.perl.org/group/perl.daily-build/ and
1035 http://www.nntp.perl.org/group/perl.daily-build.reports/ )
1036 automatically test Perl source releases on platforms with various
1039 Both efforts welcome volunteers. In order to get involved in smoke
1040 testing of the perl itself visit
1041 L<http://search.cpan.org/dist/Test-Smoke/>. In order to start smoke
1042 testing CPAN modules visit
1043 L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> or
1044 L<http://search.cpan.org/dist/minismokebox/> or
1045 L<http://search.cpan.org/dist/CPAN-Reporter/>.
1049 If you've read all the documentation in the document and the ones
1050 listed above, you're more than ready to hack on Perl.
1052 Here's some more recommendations
1058 Subscribe to perl5-porters, follow the patches and try and understand
1059 them; don't be afraid to ask if there's a portion you're not clear on -
1060 who knows, you may unearth a bug in the patch...
1064 Do read the README associated with your operating system, e.g.
1065 README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
1066 README if you find anything missing or changed over a new OS release.
1070 Find an area of Perl that seems interesting to you, and see if you can
1071 work out how it works. Scan through the source, and step over it in
1072 the debugger. Play, poke, investigate, fiddle! You'll probably get to
1073 understand not just your chosen area but a much wider range of
1074 F<perl>'s activity as well, and probably sooner than you'd think.
1078 =head2 "The Road goes ever on and on, down from the door where it began."
1080 If you can do these things, you've started on the long road to Perl
1081 porting. Thanks for wanting to help make Perl better - and happy
1084 =head2 Metaphoric Quotations
1086 If you recognized the quote about the Road above, you're in luck.
1088 Most software projects begin each file with a literal description of
1089 each file's purpose. Perl instead begins each with a literary allusion
1090 to that file's purpose.
1092 Like chapters in many books, all top-level Perl source files (along
1093 with a few others here and there) begin with an epigrammatic
1094 inscription that alludes, indirectly and metaphorically, to the
1095 material you're about to read.
1097 Quotations are taken from writings of J.R.R. Tolkien pertaining to his
1098 Legendarium, almost always from I<The Lord of the Rings>. Chapters and
1099 page numbers are given using the following editions:
1105 I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
1106 edition of 2007 was used, published in the UK by Harper Collins
1107 Publishers and in the US by the Houghton Mifflin Company.
1111 I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
1112 50th-anniversary edition of 2004 was used, published in the UK by
1113 Harper Collins Publishers and in the US by the Houghton Mifflin
1118 I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
1119 by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
1120 12 volumes in Christopher's mammoth I<History of Middle Earth>. Page
1121 numbers derive from the hardcover edition, first published in 1983 by
1122 George Allen & Unwin; no page numbers changed for the special 3-volume
1123 omnibus edition of 2002 or the various trade-paper editions, all again
1124 now by Harper Collins or Houghton Mifflin.
1128 Other JRRT books fair game for quotes would thus include I<The
1129 Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
1130 and I<The Tale of the Children of Hurin>, all but the first
1131 posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
1132 perfectly fine and probably best to quote from, provided you can find a
1133 suitable quote there.
1135 So if you were to supply a new, complete, top-level source file to add
1136 to Perl, you should conform to this peculiar practice by yourself
1137 selecting an appropriate quotation from Tolkien, retaining the original
1138 spelling and punctuation and using the same format the rest of the
1139 quotes are in. Indirect and oblique is just fine; remember, it's a
1140 metaphor, so being meta is, after all, what it's for.
1144 This document was originally written by Nathan Torkington, and is
1145 maintained by the perl5-porters mailing list.