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
41 Hack, hack, hack. Keep in mind that Perl runs on many different
42 platforms, with different operating systems that have different
43 capabilities, different filesystem organizations, and even different
44 character sets. L<perlhacktips> gives advice on this.
46 =item * Test your change
48 You can run all the tests with the following commands:
50 % ./Configure -des -Dusedevel
53 Keep hacking until the tests pass.
55 =item * Commit your change
57 Committing your work will save the change I<on your local system>:
59 % git commit -a -m 'Commit message goes here'
61 Make sure the commit message describes your change in a single
62 sentence. For example, "Fixed spelling errors in perlhack.pod".
64 =item * Send your change to perlbug
66 The next step is to submit your patch to the Perl core ticket system
69 If your changes are in a single git commit, run the following commands
70 to generate the patch file and attach it to your bug report:
73 % ./perl -Ilib utils/perlbug -p 0001-*.patch
75 The perlbug program will ask you a few questions about your email
76 address and the patch you're submitting. Once you've answered them it
77 will submit your patch via email.
79 If your changes are in multiple commits, generate a patch file for each
80 one and provide them to perlbug's C<-p> option separated by commas:
83 % ./perl -Ilib utils/perlbug -p 0001-fix1.patch,0002-fix2.patch,\
86 When prompted, pick a subject that summarizes your changes.
90 The porters appreciate the time you spent helping to make Perl better.
95 The next time you wish to make a patch, you need to start from the
96 latest perl in a pristine state. Check you don't have any local changes
97 or added files in your perl check-out which you wish to keep, then run
101 % git reset --hard origin/blead
108 If you want to report a bug in Perl, you must use the F<perlbug>
109 command line tool. This tool will ensure that your bug report includes
110 all the relevant system and configuration information.
112 To browse existing Perl bugs and patches, you can use the web interface
113 at L<http://rt.perl.org/>.
115 Please check the archive of the perl5-porters list (see below) and/or
116 the bug tracking system before submitting a bug report. Often, you'll
117 find that the bug has been reported already.
119 You can log in to the bug tracking system and comment on existing bug
120 reports. If you have additional information regarding an existing bug,
121 please add it. This will help the porters fix the bug.
123 =head1 PERL 5 PORTERS
125 The perl5-porters (p5p) mailing list is where the Perl standard
126 distribution is maintained and developed. The people who maintain Perl
127 are also referred to as the "Perl 5 Porters", "p5p" or just the
130 A searchable archive of the list is available at
131 L<http://markmail.org/search/?q=perl5-porters>. There is also an archive at
132 L<http://archive.develooper.com/perl5-porters@perl.org/>.
134 =head2 perl-changes mailing list
136 The perl5-changes mailing list receives a copy of each patch that gets
137 submitted to the maintenance and development branches of the perl
138 repository. See L<http://lists.perl.org/list/perl5-changes.html> for
139 subscription and archive information.
143 Many porters are also active on the L<irc://irc.perl.org/#p5p> channel.
144 Feel free to join the channel and ask questions about hacking on the
147 =head1 GETTING THE PERL SOURCE
149 All of Perl's source code is kept centrally in a Git repository at
150 I<perl5.git.perl.org>. The repository contains many Perl revisions
151 from Perl 1 onwards and all the revisions from Perforce, the previous
152 version control system.
154 For much more detail on using git with the Perl repository, please see
157 =head2 Read access via Git
159 You will need a copy of Git for your computer. You can fetch a copy of
160 the repository using the git protocol:
162 % git clone git://perl5.git.perl.org/perl.git perl
164 This clones the repository and makes a local copy in the F<perl>
167 If you cannot use the git protocol for firewall reasons, you can also
168 clone via http, though this is much slower:
170 % git clone http://perl5.git.perl.org/perl.git perl
172 =head2 Read access via the web
174 You may access the repository over the web. This allows you to browse
175 the tree, see recent commits, subscribe to RSS feeds for the changes,
176 search for particular commits and more. You may access it at
177 L<http://perl5.git.perl.org/perl.git>. A mirror of the repository is
178 found at L<https://github.com/Perl/perl5>.
180 =head2 Read access via rsync
182 You can also choose to use rsync to get a copy of the current source
183 tree for the bleadperl branch and all maintenance branches:
185 % rsync -avz rsync://perl5.git.perl.org/perl-current .
186 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
187 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
188 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
189 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
190 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
192 (Add the C<--delete> option to remove leftover files.)
194 To get a full list of the available sync points:
196 % rsync perl5.git.perl.org::
198 =head2 Write access via git
200 If you have a commit bit, please see L<perlgit> for more details on
205 If you're planning to do more extensive work than a single small fix,
206 we encourage you to read the documentation below. This will help you
207 focus your work and make your patches easier to incorporate into the
210 =head2 Submitting patches
212 If you have a small patch to submit, please submit it via perlbug. You
213 can also send email directly to perlbug@perl.org. Please note that
214 messages sent to perlbug may be held in a moderation queue, so you
215 won't receive a response immediately.
217 You'll know your submission has been processed when you receive an
218 email from our ticket tracking system. This email will give you a
219 ticket number. Once your patch has made it to the ticket tracking
220 system, it will also be sent to the perl5-porters@perl.org list.
222 Patches are reviewed and discussed on the p5p list. Simple,
223 uncontroversial patches will usually be applied without any discussion.
224 When the patch is applied, the ticket will be updated and you will
225 receive email. In addition, an email will be sent to the p5p list.
227 In other cases, the patch will need more work or discussion. That will
228 happen on the p5p list.
230 You are encouraged to participate in the discussion and advocate for
231 your patch. Sometimes your patch may get lost in the shuffle. It's
232 appropriate to send a reminder email to p5p if no action has been taken
233 in a month. Please remember that the Perl 5 developers are all
234 volunteers, and be polite.
236 Changes are always applied directly to the main development branch,
237 called "blead". Some patches may be backported to a maintenance
238 branch. If you think your patch is appropriate for the maintenance
239 branch (see L<perlpolicy/MAINTENANCE BRANCHES>), please explain why
242 =head2 Getting your patch accepted
244 If you are submitting a code patch there are several things that you
245 can do to help the Perl 5 Porters accept your patch.
249 If you used git to check out the Perl source, then using C<git
250 format-patch> will produce a patch in a style suitable for Perl. The
251 C<format-patch> command produces one patch file for each commit you
252 made. If you prefer to send a single patch for all commits, you can
257 % git diff blead my-branch-name
259 This produces a patch based on the difference between blead and your
260 current branch. It's important to make sure that blead is up to date
261 before producing the diff, that's why we call C<git pull> first.
263 We strongly recommend that you use git if possible. It will make your
264 life easier, and ours as well.
266 However, if you're not using git, you can still produce a suitable
267 patch. You'll need a pristine copy of the Perl source to diff against.
268 The porters prefer unified diffs. Using GNU C<diff>, you can produce a
271 % diff -Npurd perl.pristine perl.mine
273 Make sure that you C<make realclean> in your copy of Perl to remove any
274 build artifacts, or you may get a confusing result.
276 =head3 Commit message
278 As you craft each patch you intend to submit to the Perl core, it's
279 important to write a good commit message. This is especially important
280 if your submission will consist of a series of commits.
282 The first line of the commit message should be a short description
283 without a period. It should be no longer than the subject line of an
284 email, 50 characters being a good rule of thumb.
286 A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
287 only display the first line (cut off at 50 characters) when presenting
290 The commit message should include a description of the problem that the
291 patch corrects or new functionality that the patch adds.
293 As a general rule of thumb, your commit message should help a
294 programmer who knows the Perl core quickly understand what you were
295 trying to do, how you were trying to do it, and why the change matters
302 Your commit message should describe why the change you are making is
303 important. When someone looks at your change in six months or six
304 years, your intent should be clear.
306 If you're deprecating a feature with the intent of later simplifying
307 another bit of code, say so. If you're fixing a performance problem or
308 adding a new feature to support some other bit of the core, mention
313 Your commit message should describe what part of the Perl core you're
314 changing and what you expect your patch to do.
318 While it's not necessary for documentation changes, new tests or
319 trivial patches, it's often worth explaining how your change works.
320 Even if it's clear to you today, it may not be clear to a porter next
325 A commit message isn't intended to take the place of comments in your
326 code. Commit messages should describe the change you made, while code
327 comments should describe the current state of the code.
329 If you've just implemented a new feature, complete with doc, tests and
330 well-commented code, a brief commit message will often suffice. If,
331 however, you've just changed a single character deep in the parser or
332 lexer, you might need to write a small novel to ensure that future
333 readers understand what you did and why you did it.
335 =head3 Comments, Comments, Comments
337 Be sure to adequately comment your code. While commenting every line
338 is unnecessary, anything that takes advantage of side effects of
339 operators, that creates changes that will be felt outside of the
340 function being patched, or that others may find confusing should be
341 documented. If you are going to err, it is better to err on the side
342 of adding too many comments than too few.
344 The best comments explain I<why> the code does what it does, not I<what
349 In general, please follow the particular style of the code you are
352 In particular, follow these general guidelines for patching Perl
359 8-wide tabs (no exceptions!)
363 4-wide indents for code, 2-wide indents for nested CPP #defines
367 Try hard not to exceed 79-columns
375 Uncuddled elses and "K&R" style for indenting control constructs
379 No C++ style (//) comments
383 Mark places that need to be revisited with XXX (and revisit often!)
387 Opening brace lines up with "if" when conditional spans multiple lines;
388 should be at end-of-line otherwise
392 In function definitions, name starts in column 0 (return value-type is on
397 Single space after keywords that are followed by parens, no space
398 between function name and following paren
402 Avoid assignments in conditionals, but if they're unavoidable, use
403 extra paren, e.g. "if (a && (b = c)) ..."
407 "return foo;" rather than "return(foo);"
411 "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
415 Do not declare variables using "register". It may be counterproductive
416 with modern compilers, and is deprecated in C++, under which the Perl
417 source is regularly compiled.
421 In-line functions that are in headers that are accessible to XS code
422 need to be able to compile without warnings with commonly used extra
423 compilation flags, such as gcc's C<-Wswitch-default> which warns
424 whenever a switch statement does not have a "default" case. The use of
425 these extra flags is to catch potential problems in legal C code, and
426 is often used by Perl aggregators, such as Linux distributors.
432 If your patch changes code (rather than just changing documentation),
433 you should also include one or more test cases which illustrate the bug
434 you're fixing or validate the new functionality you're adding. In
435 general, you should update an existing test file rather than create a
438 Your test suite additions should generally follow these guidelines
439 (courtesy of Gurusamy Sarathy <gsar@activestate.com>):
445 Know what you're testing. Read the docs, and the source.
449 Tend to fail, not succeed.
453 Interpret results strictly.
457 Use unrelated features (this will flush out bizarre interactions).
461 Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
465 Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
466 found in t/op/tie.t is much more maintainable, and gives better failure
471 Give meaningful error messages when a test fails.
475 Avoid using qx// and system() unless you are testing for them. If you
476 do use them, make sure that you cover _all_ perl platforms.
480 Unlink any temporary files you create.
484 Promote unforeseen warnings to errors with $SIG{__WARN__}.
488 Be sure to use the libraries and modules shipped with the version being
489 tested, not those that were already installed.
493 Add comments to the code explaining what you are testing for.
497 Make updating the '1..42' string unnecessary. Or make sure that you
502 Test _all_ behaviors of a given operator, library, or function.
504 Test all optional arguments.
506 Test return values in various contexts (boolean, scalar, list, lvalue).
508 Use both global and lexical variables.
510 Don't forget the exceptional, pathological cases.
514 =head2 Patching a core module
516 This works just like patching anything else, with one extra
519 Modules in the F<cpan/> directory of the source tree are maintained
520 outside of the Perl core. When the author updates the module, the
521 updates are simply copied into the core. See that module's
522 documentation or its listing on L<http://search.cpan.org/> for more
523 information on reporting bugs and submitting patches.
525 In most cases, patches to modules in F<cpan/> should be sent upstream
526 and should not be applied to the Perl core individually. If a patch to
527 a file in F<cpan/> absolutely cannot wait for the fix to be made
528 upstream, released to CPAN and copied to blead, you must add (or
529 update) a C<CUSTOMIZED> entry in the F<"Porting/Maintainers.pl"> file
530 to flag that a local modification has been made. See
531 F<"Porting/Maintainers.pl"> for more details.
533 In contrast, modules in the F<dist/> directory are maintained in the
536 =head2 Updating perldelta
538 For changes significant enough to warrant a F<pod/perldelta.pod> entry,
539 the porters will greatly appreciate it if you submit a delta entry
540 along with your actual change. Significant changes include, but are
547 Adding, deprecating, or removing core features
551 Adding, deprecating, removing, or upgrading core or dual-life modules
555 Adding new core tests
559 Fixing security issues and user-visible bugs in the core
563 Changes that might break existing code, either on the perl or C level
567 Significant performance improvements
571 Adding, removing, or significantly changing documentation in the
576 Important platform-specific changes
580 Please make sure you add the perldelta entry to the right section
581 within F<pod/perldelta.pod>. More information on how to write good
582 perldelta entries is available in the C<Style> section of
583 F<Porting/how_to_write_a_perldelta.pod>.
585 =head2 What makes for a good patch?
587 New features and extensions to the language can be contentious. There
588 is no specific set of criteria which determine what features get added,
589 but here are some questions to consider when developing a patch:
591 =head3 Does the concept match the general goals of Perl?
593 Our goals include, but are not limited to:
599 Keep it fast, simple, and useful.
603 Keep features/concepts as orthogonal as possible.
607 No arbitrary limits (platforms, data sizes, cultures).
611 Keep it open and exciting to use/patch/advocate Perl everywhere.
615 Either assimilate new technologies, or build bridges to them.
619 =head3 Where is the implementation?
621 All the talk in the world is useless without an implementation. In
622 almost every case, the person or people who argue for a new feature
623 will be expected to be the ones who implement it. Porters capable of
624 coding new features have their own agendas, and are not available to
625 implement your (possibly good) idea.
627 =head3 Backwards compatibility
629 It's a cardinal sin to break existing Perl programs. New warnings can
630 be contentious--some say that a program that emits warnings is not
631 broken, while others say it is. Adding keywords has the potential to
632 break programs, changing the meaning of existing token sequences or
633 functions might break programs.
635 The Perl 5 core includes mechanisms to help porters make backwards
636 incompatible changes more compatible such as the L<feature> and
637 L<deprecate> modules. Please use them when appropriate.
639 =head3 Could it be a module instead?
641 Perl 5 has extension mechanisms, modules and XS, specifically to avoid
642 the need to keep changing the Perl interpreter. You can write modules
643 that export functions, you can give those functions prototypes so they
644 can be called like built-in functions, you can even write XS code to
645 mess with the runtime data structures of the Perl interpreter if you
646 want to implement really complicated things.
648 Whenever possible, new features should be prototyped in a CPAN module
649 before they will be considered for the core.
651 =head3 Is the feature generic enough?
653 Is this something that only the submitter wants added to the language,
654 or is it broadly useful? Sometimes, instead of adding a feature with a
655 tight focus, the porters might decide to wait until someone implements
656 the more generalized feature.
658 =head3 Does it potentially introduce new bugs?
660 Radical rewrites of large chunks of the Perl interpreter have the
661 potential to introduce new bugs.
663 =head3 How big is it?
665 The smaller and more localized the change, the better. Similarly, a
666 series of small patches is greatly preferred over a single large patch.
668 =head3 Does it preclude other desirable features?
670 A patch is likely to be rejected if it closes off future avenues of
671 development. For instance, a patch that placed a true and final
672 interpretation on prototypes is likely to be rejected because there are
673 still options for the future of prototypes that haven't been addressed.
675 =head3 Is the implementation robust?
677 Good patches (tight code, complete, correct) stand more chance of going
678 in. Sloppy or incorrect patches might be placed on the back burner
679 until the pumpking has time to fix, or might be discarded altogether
680 without further notice.
682 =head3 Is the implementation generic enough to be portable?
684 The worst patches make use of system-specific features. It's highly
685 unlikely that non-portable additions to the Perl language will be
688 =head3 Is the implementation tested?
690 Patches which change behaviour (fixing bugs or introducing new
691 features) must include regression tests to verify that everything works
694 Without tests provided by the original author, how can anyone else
695 changing perl in the future be sure that they haven't unwittingly
696 broken the behaviour the patch implements? And without tests, how can
697 the patch's author be confident that his/her hard work put into the
698 patch won't be accidentally thrown away by someone in the future?
700 =head3 Is there enough documentation?
702 Patches without documentation are probably ill-thought out or
703 incomplete. No features can be added or changed without documentation,
704 so submitting a patch for the appropriate pod docs as well as the
705 source code is important.
707 =head3 Is there another way to do it?
709 Larry said "Although the Perl Slogan is I<There's More Than One Way to
710 Do It>, I hesitate to make 10 ways to do something". This is a tricky
711 heuristic to navigate, though--one man's essential addition is another
712 man's pointless cruft.
714 =head3 Does it create too much work?
716 Work for the pumpking, work for Perl programmers, work for module
717 authors, ... Perl is supposed to be easy.
719 =head3 Patches speak louder than words
721 Working code is always preferred to pie-in-the-sky ideas. A patch to
722 add a feature stands a much higher chance of making it to the language
723 than does a random feature request, no matter how fervently argued the
724 request might be. This ties into "Will it be useful?", as the fact
725 that someone took the time to make the patch demonstrates a strong
726 desire for the feature.
730 The core uses the same testing style as the rest of Perl, a simple
731 "ok/not ok" run through Test::Harness, but there are a few special
734 There are three ways to write a test in the core: L<Test::More>,
735 F<t/test.pl> and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">.
736 The decision of which to use depends on what part of the test suite
737 you're working on. This is a measure to prevent a high-level failure
738 (such as Config.pm breaking) from causing basic functionality tests to
741 The F<t/test.pl> library provides some of the features of
742 L<Test::More>, but avoids loading most modules and uses as few core
743 features as possible.
745 If you write your own test, use the L<Test Anything
746 Protocol|http://testanything.org>.
750 =item * F<t/base>, F<t/comp> and F<t/opbasic>
752 Since we don't know if C<require> works, or even subroutines, use ad hoc
753 tests for these three. Step carefully to avoid using the feature being
754 tested. Tests in F<t/opbasic>, for instance, have been placed there
755 rather than in F<t/op> because they test functionality which
756 F<t/test.pl> presumes has already been demonstrated to work.
758 =item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
760 Now that basic require() and subroutines are tested, you can use the
761 F<t/test.pl> library.
763 You can also use certain libraries like Config conditionally, but be
764 sure to skip the test gracefully if it's not there.
766 =item * Everything else
768 Now that the core of Perl is tested, L<Test::More> can and should be
769 used. You can also use the full suite of core modules in the tests.
773 When you say "make test", Perl uses the F<t/TEST> program to run the
774 test suite (except under Win32 where it uses F<t/harness> instead).
775 All tests are run from the F<t/> directory, B<not> the directory which
776 contains the test. This causes some problems with the tests in
777 F<lib/>, so here's some opportunity for some patching.
779 You must be triply conscious of cross-platform concerns. This usually
780 boils down to using L<File::Spec>, avoiding things like C<fork()>
781 and C<system()> unless absolutely necessary, and not assuming that a
782 given character has a particular ordinal value (code point) or that its
783 UTF-8 representation is composed of particular bytes.
785 There are several functions available to specify characters and code
786 points portably in tests. The always-preloaded functions
787 C<utf8::unicode_to_native()> and its inverse
788 C<utf8::native_to_unicode()> take code points and translate
789 appropriately. The file F<t/charset_tools.pl> has several functions
790 that can be useful. It has versions of the previous two functions
791 that take strings as inputs -- not single numeric code points:
792 C<uni_to_native()> and C<native_to_uni()>. If you must look at the
793 individual bytes comprising a UTF-8 encoded string,
794 C<byte_utf8a_to_utf8n()> takes as input a string of those bytes encoded
795 for an ASCII platform, and returns the equivalent string in the native
796 platform. For example, C<byte_utf8a_to_utf8n("\xC2\xA0")> returns the
797 byte sequence on the current platform that form the UTF-8 for C<U+00A0>,
798 since C<"\xC2\xA0"> are the UTF-8 bytes on an ASCII platform for that
799 code point. This function returns C<"\xC2\xA0"> on an ASCII platform, and
800 C<"\x80\x41"> on an EBCDIC 1047 one.
802 But easiest is, if the character is specifiable as a literal, like
803 C<"A"> or C<"%">, to use that; if not so specificable, you can use use
804 C<\N{}> , if the side effects aren't troublesome. Simply specify all
805 your characters in hex, using C<\N{U+ZZ}> instead of C<\xZZ>. C<\N{}>
806 is the Unicode name, and so it
807 always gives you the Unicode character. C<\N{U+41}> is the character
808 whose Unicode code point is C<0x41>, hence is C<'A'> on all platforms.
809 The side effects are:
815 These select Unicode rules. That means that in double-quotish strings,
816 the string is always converted to UTF-8 to force a Unicode
817 interpretation (you can C<utf8::downgrade()> afterwards to convert back
818 to non-UTF8, if possible). In regular expression patterns, the
819 conversion isn't done, but if the character set modifier would
820 otherwise be C</d>, it is changed to C</u>.
824 If you use the form C<\N{I<character name>}>, the L<charnames> module
825 gets automatically loaded. This may not be suitable for the test level
830 If you are testing locales (see L<perllocale>), there are helper
831 functions in F<t/loc_tools.pl> to enable you to see what locales there
832 are on the current platform.
834 =head2 Special C<make test> targets
836 There are various special make targets that can be used to test Perl
837 slightly differently than the standard "test" target. Not all them are
838 expected to give a 100% success rate. Many of them have several
839 aliases, and many of them are not available on certain operating
846 This runs some basic sanity tests on the source tree and helps catch
847 basic errors before you submit a patch.
851 Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
852 F<t/op>, F<t/uni> and F<t/mro> tests.
854 =item * test.valgrind check.valgrind
856 (Only in Linux) Run all the tests using the memory leak + naughty
857 memory access tool "valgrind". The log files will be named
858 F<testname.valgrind>.
862 Run the test suite with the F<t/harness> controlling program, instead
863 of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
864 L<Test::Harness> module, thus using this test target supposes that perl
865 mostly works. The main advantage for our purposes is that it prints a
866 detailed summary of failed tests at the end. Also, unlike F<t/TEST>,
867 it doesn't redirect stderr to stdout.
869 Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
870 so there is no special "test_harness" target.
872 Under Win32's "test" target you may use the TEST_SWITCHES and
873 TEST_FILES environment variables to control the behaviour of
874 F<t/harness>. This means you can say
876 nmake test TEST_FILES="op/*.t"
877 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
879 =item * test-notty test_notty
881 Sets PERL_SKIP_TTY_TEST to true before running normal test.
885 =head2 Parallel tests
887 The core distribution can now run its regression tests in parallel on
888 Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
889 in your environment to the number of tests to run in parallel, and run
890 C<make test_harness>. On a Bourne-like shell, this can be done as
892 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
894 An environment variable is used, rather than parallel make itself,
895 because L<TAP::Harness> needs to be able to schedule individual
896 non-conflicting test scripts itself, and there is no standard interface
897 to C<make> utilities to interact with their job schedulers.
899 Note that currently some test scripts may fail when run in parallel
900 (most notably F<dist/IO/t/io_dir.t>). If necessary, run just the
901 failing scripts again sequentially and see if the failures go away.
903 =head2 Running tests by hand
905 You can run part of the test suite by hand by using one of the
906 following commands from the F<t/> directory:
908 ./perl -I../lib TEST list-of-.t-files
912 ./perl -I../lib harness list-of-.t-files
914 (If you don't specify test scripts, the whole test suite will be run.)
916 =head2 Using F<t/harness> for testing
918 If you use C<harness> for testing, you have several command line
919 options available to you. The arguments are as follows, and are in the
920 order that they must appear if used together.
922 harness -v -torture -re=pattern LIST OF FILES TO TEST
923 harness -v -torture -re LIST OF PATTERNS TO MATCH
925 If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
926 the manifest. The file list may include shell wildcards which will be
933 Run the tests under verbose mode so you can see what tests were run,
938 Run the torture tests as well as the normal set.
942 Filter the file list so that all the test files run match PATTERN.
943 Note that this form is distinct from the B<-re LIST OF PATTERNS> form
944 below in that it allows the file list to be provided as well.
946 =item * -re LIST OF PATTERNS
948 Filter the file list so that all the test files run match
949 /(LIST|OF|PATTERNS)/. Note that with this form the patterns are joined
950 by '|' and you cannot supply a list of files, instead the test files
951 are obtained from the MANIFEST.
955 You can run an individual test by a command similar to
957 ./perl -I../lib path/to/foo.t
959 except that the harnesses set up some environment variables that may
960 affect the execution of the test:
966 indicates that we're running this test as part of the perl core test
967 suite. This is useful for modules that have a dual life on CPAN.
969 =item * PERL_DESTRUCT_LEVEL=2
971 is set to 2 if it isn't set already (see
972 L<perlhacktips/PERL_DESTRUCT_LEVEL>).
976 (used only by F<t/TEST>) if set, overrides the path to the perl
977 executable that should be used to run the tests (the default being
980 =item * PERL_SKIP_TTY_TEST
982 if set, tells to skip the tests that need a terminal. It's actually
983 set automatically by the Makefile, but can also be forced artificially
984 by running 'make test_notty'.
988 =head3 Other environment variables that may influence tests
992 =item * PERL_TEST_Net_Ping
994 Setting this variable runs all the Net::Ping modules tests, otherwise
995 some tests that interact with the outside world are skipped. See
998 =item * PERL_TEST_NOVREXX
1000 Setting this variable skips the vrexx.t tests for OS2::REXX.
1002 =item * PERL_TEST_NUMCONVERTS
1004 This sets a variable in op/numconvert.t.
1006 =item * PERL_TEST_MEMORY
1008 Setting this variable includes the tests in F<t/bigmem/>. This should
1009 be set to the number of gigabytes of memory available for testing, eg.
1010 C<PERL_TEST_MEMORY=4> indicates that tests that require 4GiB of
1011 available memory can be run safely.
1015 See also the documentation for the Test and Test::Harness modules, for
1016 more environment variables that affect testing.
1018 =head2 Performance testing
1020 The file F<t/perf/benchmarks> contains snippets of perl code which are
1021 intended to be benchmarked across a range of perls by the
1022 F<Porting/bench.pl> tool. If you fix or enhance a performance issue, you
1023 may want to add a representative code sample to the file, then run
1024 F<bench.pl> against the previous and current perls to see what difference
1025 it has made, and whether anything else has slowed down as a consequence.
1027 The file F<t/perf/opcount.t> is designed to test whether a particular
1028 code snippet has been compiled into an optree containing specified
1029 numbers of particular op types. This is good for testing whether
1030 optimisations which alter ops, such as converting an C<aelem> op into an
1031 C<aelemfast> op, are really doing that.
1033 The files F<t/perf/speed.t> and F<t/re/speed.t> are designed to test
1034 things that run thousands of times slower if a particular optimisation
1035 is broken (for example, the utf8 length cache on long utf8 strings).
1036 Add a test that will take a fraction of a second normally, and minutes
1037 otherwise, causing the test file to time out on failure.
1039 =head1 MORE READING FOR GUTS HACKERS
1041 To hack on the Perl guts, you'll need to read the following things:
1045 =item * L<perlsource>
1047 An overview of the Perl source tree. This will help you find the files
1050 =item * L<perlinterp>
1052 An overview of the Perl interpreter source code and some details on how
1053 Perl does what it does.
1055 =item * L<perlhacktut>
1057 This document walks through the creation of a small patch to Perl's C
1058 code. If you're just getting started with Perl core hacking, this will
1059 help you understand how it works.
1061 =item * L<perlhacktips>
1063 More details on hacking the Perl core. This document focuses on lower
1064 level details such as how to write tests, compilation issues,
1065 portability, debugging, etc.
1067 If you plan on doing serious C hacking, make sure to read this.
1071 This is of paramount importance, since it's the documentation of what
1072 goes where in the Perl source. Read it over a couple of times and it
1073 might start to make sense - don't worry if it doesn't yet, because the
1074 best way to study it is to read it in conjunction with poking at Perl
1075 source, and we'll do that later on.
1077 Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very
1080 L<http://search.cpan.org/dist/illguts/>
1082 =item * L<perlxstut> and L<perlxs>
1084 A working knowledge of XSUB programming is incredibly useful for core
1085 hacking; XSUBs use techniques drawn from the PP code, the portion of
1086 the guts that actually executes a Perl program. It's a lot gentler to
1087 learn those techniques from simple examples and explanation than from
1092 The documentation for the Perl API explains what some of the internal
1093 functions do, as well as the many macros used in the source.
1095 =item * F<Porting/pumpkin.pod>
1097 This is a collection of words of wisdom for a Perl porter; some of it
1098 is only useful to the pumpkin holder, but most of it applies to anyone
1099 wanting to go about Perl development.
1103 =head1 CPAN TESTERS AND PERL SMOKERS
1105 The CPAN testers ( http://testers.cpan.org/ ) are a group of volunteers
1106 who test CPAN modules on a variety of platforms.
1108 Perl Smokers ( http://www.nntp.perl.org/group/perl.daily-build/ and
1109 http://www.nntp.perl.org/group/perl.daily-build.reports/ )
1110 automatically test Perl source releases on platforms with various
1113 Both efforts welcome volunteers. In order to get involved in smoke
1114 testing of the perl itself visit
1115 L<http://search.cpan.org/dist/Test-Smoke/>. In order to start smoke
1116 testing CPAN modules visit
1117 L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> or
1118 L<http://search.cpan.org/dist/minismokebox/> or
1119 L<http://search.cpan.org/dist/CPAN-Reporter/>.
1123 If you've read all the documentation in the document and the ones
1124 listed above, you're more than ready to hack on Perl.
1126 Here's some more recommendations
1132 Subscribe to perl5-porters, follow the patches and try and understand
1133 them; don't be afraid to ask if there's a portion you're not clear on -
1134 who knows, you may unearth a bug in the patch...
1138 Do read the README associated with your operating system, e.g.
1139 README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
1140 README if you find anything missing or changed over a new OS release.
1144 Find an area of Perl that seems interesting to you, and see if you can
1145 work out how it works. Scan through the source, and step over it in
1146 the debugger. Play, poke, investigate, fiddle! You'll probably get to
1147 understand not just your chosen area but a much wider range of
1148 F<perl>'s activity as well, and probably sooner than you'd think.
1152 =head2 "The Road goes ever on and on, down from the door where it began."
1154 If you can do these things, you've started on the long road to Perl
1155 porting. Thanks for wanting to help make Perl better - and happy
1158 =head2 Metaphoric Quotations
1160 If you recognized the quote about the Road above, you're in luck.
1162 Most software projects begin each file with a literal description of
1163 each file's purpose. Perl instead begins each with a literary allusion
1164 to that file's purpose.
1166 Like chapters in many books, all top-level Perl source files (along
1167 with a few others here and there) begin with an epigrammatic
1168 inscription that alludes, indirectly and metaphorically, to the
1169 material you're about to read.
1171 Quotations are taken from writings of J.R.R. Tolkien pertaining to his
1172 Legendarium, almost always from I<The Lord of the Rings>. Chapters and
1173 page numbers are given using the following editions:
1179 I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
1180 edition of 2007 was used, published in the UK by Harper Collins
1181 Publishers and in the US by the Houghton Mifflin Company.
1185 I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
1186 50th-anniversary edition of 2004 was used, published in the UK by
1187 Harper Collins Publishers and in the US by the Houghton Mifflin
1192 I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
1193 by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
1194 12 volumes in Christopher's mammoth I<History of Middle Earth>. Page
1195 numbers derive from the hardcover edition, first published in 1983 by
1196 George Allen & Unwin; no page numbers changed for the special 3-volume
1197 omnibus edition of 2002 or the various trade-paper editions, all again
1198 now by Harper Collins or Houghton Mifflin.
1202 Other JRRT books fair game for quotes would thus include I<The
1203 Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
1204 and I<The Tale of the Children of Hurin>, all but the first
1205 posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
1206 perfectly fine and probably best to quote from, provided you can find a
1207 suitable quote there.
1209 So if you were to supply a new, complete, top-level source file to add
1210 to Perl, you should conform to this peculiar practice by yourself
1211 selecting an appropriate quotation from Tolkien, retaining the original
1212 spelling and punctuation and using the same format the rest of the
1213 quotes are in. Indirect and oblique is just fine; remember, it's a
1214 metaphor, so being meta is, after all, what it's for.
1218 This document was originally written by Nathan Torkington, and is
1219 maintained by the perl5-porters mailing list.