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 it
68 will submit your patch via email.
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>
80 command line tool. This tool will ensure that your bug report includes
81 all the 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
101 A searchable archive of the list is available at
102 L<http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/>. There is
103 also another archive at
104 L<http://archive.develooper.com/perl5-porters@perl.org/>.
106 =head2 perl-changes mailing list
108 The perl5-changes mailing list receives a copy of each patch that gets
109 submitted to the maintenance and development branches of the perl
110 repository. See L<http://lists.perl.org/list/perl5-changes.html> for
111 subscription and archive information.
115 Many porters are also active on the L<irc://irc.perl.org/#p5p> channel.
116 Feel free to join the channel and ask questions about hacking on the
119 =head1 GETTING THE PERL SOURCE
121 All of Perl's source code is kept centrally in a Git repository at
122 I<perl5.git.perl.org>. The repository contains many Perl revisions from
123 Perl 1 onwards and all the revisions from Perforce, the previous
124 version control system.
126 For much more detail on using git with the Perl repository, please see
129 =head2 Read access via Git
131 You will need a copy of Git for your computer. You can fetch a copy of
132 the repository using the git protocol:
134 % git clone git://perl5.git.perl.org/perl.git perl
136 This clones the repository and makes a local copy in the F<perl>
139 If you cannot use the git protocol for firewall reasons, you can also
140 clone via http, though this is much slower:
142 % git clone http://perl5.git.perl.org/perl.git perl
144 =head2 Read access via the web
146 You may access the repository over the web. This allows you to browse
147 the tree, see recent commits, subscribe to RSS feeds for the changes,
148 search for particular commits and more. You may access it at
149 L<http://perl5.git.perl.org/perl.git>. A mirror of the repository is
150 found at L<http://github.com/mirrors/perl>.
152 =head2 Read access via rsync
154 You can also choose to use rsync to get a copy of the current source
155 tree for the bleadperl branch and all maintenance branches:
157 % rsync -avz rsync://perl5.git.perl.org/perl-current .
158 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
159 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
160 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
161 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
162 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
164 (Add the C<--delete> option to remove leftover files.)
166 To get a full list of the available sync points:
168 % rsync perl5.git.perl.org::
170 =head2 Write access via git
172 If you have a commit bit, please see L<perlgit> for more details on
177 If you're planning to do more extensive work than a single small fix,
178 we encourage you to read the documentation below. This will help you
179 focus your work and make your patches easier to incorporate into the
182 =head2 Submitting patches
184 If you have a small patch to submit, please submit it via perlbug. You
185 can also send email directly to perlbug@perl.org. Please note that
186 messages sent to perlbug may be held in a moderation queue, so you
187 won't receive a response immediately.
189 You'll know your submission has been processed when you receive an
190 email from our ticket tracking system. This email will give you a
191 ticket number. Once your patch has made it to the ticket tracking
192 system, it will also be sent to the perl5-porters@perl.org list.
194 Patches are reviewed and discussed on the p5p list. Simple,
195 uncontroversial patches will usually be applied without any discussion.
196 When the patch is applied, the ticket will be updated and you will
197 receive email. In addition, an email will be sent to the p5p list.
199 In other cases, the patch will need more work or discussion. That will
200 happen on the p5p list.
202 You are encouraged to participate in the discussion and advocate for
203 your patch. Sometimes your patch may get lost in the shuffle. It's
204 appropriate to send a reminder email to p5p if no action has been taken
205 in a month. Please remember that the Perl 5 developers are all
206 volunteers, and be polite.
208 Changes are always applied directly to the main development branch,
209 called "blead". Some patches may be backported to a maintenance branch.
210 If you think your patch is appropriate for the maintenance branch,
211 please explain why when you submit it.
213 =head2 Getting your patch accepted
215 If you are submitting a code patch there are several things that you
216 can do to help the Perl 5 Porters accept your patch.
220 If you used git to check out the Perl source, then using C<git
221 format-patch> will produce a patch in a style suitable for Perl. The
222 C<format-patch> command produces one patch file for each commit you
223 made. If you prefer to send a single patch for all commits, you can use
228 % git diff blead my-branch-name
230 This produces a patch based on the difference between blead and your
231 current branch. It's important to make sure that blead is up to date
232 before producing the diff, that's why we call C<git pull> first.
234 We strongly recommend that you use git if possible. It will make your
235 life easier, and ours as well.
237 However, if you're not using git, you can still produce a suitable
238 patch. You'll need a pristine copy of the Perl source to diff against.
239 The porters prefer unified diffs. Using GNU C<diff>, you can produce a
242 % diff -Npurd perl.pristine perl.mine
244 Make sure that you C<make realclean> in your copy of Perl to remove any
245 build artifacts, or you may get a confusing result.
247 =head3 Commit message
249 As you craft each patch you intend to submit to the Perl core, it's
250 important to write a good commit message. This is especially important
251 if your submission will consist of a series of commits.
253 The first line of the commit message should be a short description
254 without a period. It should be no longer than the subject line of an
255 email, 50 characters being a good rule of thumb.
257 A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
258 only display the first line (cut off at 50 characters) when presenting
261 The commit message should include a description of the problem that the
262 patch corrects or new functionality that the patch adds.
264 As a general rule of thumb, your commit message should help a
265 programmer who knows the Perl core quickly understand what you were
266 trying to do, how you were trying to do it, and why the change matters
273 Your commit message should describe why the change you are making is
274 important. When someone looks at your change in six months or six
275 years, your intent should be clear.
277 If you're deprecating a feature with the intent of later simplifying
278 another bit of code, say so. If you're fixing a performance problem or
279 adding a new feature to support some other bit of the core, mention
284 Your commit message should describe what part of the Perl core you're
285 changing and what you expect your patch to do.
289 While it's not necessary for documentation changes, new tests or
290 trivial patches, it's often worth explaining how your change works.
291 Even if it's clear to you today, it may not be clear to a porter next
296 A commit message isn't intended to take the place of comments in your
297 code. Commit messages should describe the change you made, while code
298 comments should describe the current state of the code.
300 If you've just implemented a new feature, complete with doc, tests and
301 well-commented code, a brief commit message will often suffice. If,
302 however, you've just changed a single character deep in the parser or
303 lexer, you might need to write a small novel to ensure that future
304 readers understand what you did and why you did it.
306 =head3 Comments, Comments, Comments
308 Be sure to adequately comment your code. While commenting every line is
309 unnecessary, anything that takes advantage of side effects of
310 operators, that creates changes that will be felt outside of the
311 function being patched, or that others may find confusing should be
312 documented. If you are going to err, it is better to err on the side of
313 adding too many comments than too few.
315 The best comments explain I<why> the code does what it does, not I<what
320 In general, please follow the particular style of the code you are
323 In particular, follow these general guidelines for patching Perl
330 8-wide tabs (no exceptions!)
334 4-wide indents for code, 2-wide indents for nested CPP #defines
338 Try hard not to exceed 79-columns
346 Uncuddled elses and "K&R" style for indenting control constructs
350 No C++ style (//) comments
354 Mark places that need to be revisited with XXX (and revisit often!)
358 Opening brace lines up with "if" when conditional spans multiple lines;
359 should be at end-of-line otherwise
363 In function definitions, name starts in column 0 (return value is on
368 Single space after keywords that are followed by parens, no space
369 between function name and following paren
373 Avoid assignments in conditionals, but if they're unavoidable, use
374 extra paren, e.g. "if (a && (b = c)) ..."
378 "return foo;" rather than "return(foo);"
382 "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
386 Do not declare variables using "register". It may be counterproductive
387 with modern compilers, and is deprecated in C++, under which the Perl
388 source is regularly compiled.
394 If your patch changes code (rather than just changing documentation),
395 you should also include one or more test cases which illustrate the bug
396 you're fixing or validate the new functionality you're adding. In
397 general, you should update an existing test file rather than create a
400 Your test suite additions should generally follow these guidelines
401 (courtesy of Gurusamy Sarathy <gsar@activestate.com>):
407 Know what you're testing. Read the docs, and the source.
411 Tend to fail, not succeed.
415 Interpret results strictly.
419 Use unrelated features (this will flush out bizarre interactions).
423 Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
427 Avoid using hardcoded test numbers whenever possible (the EXPECTED/GOT
428 found in t/op/tie.t is much more maintainable, and gives better failure
433 Give meaningful error messages when a test fails.
437 Avoid using qx// and system() unless you are testing for them. If you
438 do use them, make sure that you cover _all_ perl platforms.
442 Unlink any temporary files you create.
446 Promote unforeseen warnings to errors with $SIG{__WARN__}.
450 Be sure to use the libraries and modules shipped with the version being
451 tested, not those that were already installed.
455 Add comments to the code explaining what you are testing for.
459 Make updating the '1..42' string unnecessary. Or make sure that you
464 Test _all_ behaviors of a given operator, library, or function.
466 Test all optional arguments.
468 Test return values in various contexts (boolean, scalar, list, lvalue).
470 Use both global and lexical variables.
472 Don't forget the exceptional, pathological cases.
476 =head2 Patching a core module
478 This works just like patching anything else, with one extra
481 Modules in the F<cpan/> directory of the source tree are maintained
482 outside of the Perl core. When the author updates the module, the
483 updates are simply copied into the core. See that module's
484 documentation or its listing on L<http://search.cpan.org/> for more
485 information on reporting bugs and submitting patches.
487 In most cases, patches to modules in F<cpan/> should be sent upstream
488 and should not be applied to the Perl core individually. If a patch to
489 a file in F<cpan/> absolutely cannot wait for the fix to be made
490 upstream, released to CPAN and copied to blead, you must add (or
491 update) a C<CUSTOMIZED> entry in the F<"Porting/Maintainers.pl"> file
492 to flag that a local modification has been made. See
493 F<"Porting/Maintainers.pl"> for more details.
495 In contrast, modules in the F<dist/> directory are maintained in the
498 =head2 Updating perldelta
500 For changes significant enough to warrant a F<pod/perldelta.pod> entry,
501 the porters will greatly appreciate it if you submit a delta entry
502 along with your actual change. Significant changes include, but are not
509 Adding, deprecating, or removing core features
513 Adding, deprecating, removing, or upgrading core or dual-life modules
517 Adding new core tests
521 Fixing security issues and user-visible bugs in the core
525 Changes that might break existing code, either on the perl or C level
529 Significant performance improvements
533 Adding, removing, or significantly changing documentation in the
538 Important platform-specific changes
542 Please make sure you add the perldelta entry to the right section
543 within F<pod/perldelta.pod>. More information on how to write good
544 perldelta entries is available in the C<Style> section of
545 F<Porting/how_to_write_a_perldelta.pod>.
547 =head2 What makes for a good patch?
549 New features and extensions to the language can be contentious. There
550 is no specific set of criteria which determine what features get added,
551 but here are some questions to consider when developing a patch:
553 =head3 Does the concept match the general goals of Perl?
555 Our goals include, but are not limited to:
561 Keep it fast, simple, and useful.
565 Keep features/concepts as orthogonal as possible.
569 No arbitrary limits (platforms, data sizes, cultures).
573 Keep it open and exciting to use/patch/advocate Perl everywhere.
577 Either assimilate new technologies, or build bridges to them.
581 =head3 Where is the implementation?
583 All the talk in the world is useless without an implementation. In
584 almost every case, the person or people who argue for a new feature
585 will be expected to be the ones who implement it. Porters capable of
586 coding new features have their own agendas, and are not available to
587 implement your (possibly good) idea.
589 =head3 Backwards compatibility
591 It's a cardinal sin to break existing Perl programs. New warnings can
592 be contentious--some say that a program that emits warnings is not
593 broken, while others say it is. Adding keywords has the potential to
594 break programs, changing the meaning of existing token sequences or
595 functions might break programs.
597 The Perl 5 core includes mechanisms to help porters make backwards
598 incompatible changes more compatible such as the L<feature> and
599 L<deprecate> modules. Please use them when appropriate.
601 =head3 Could it be a module instead?
603 Perl 5 has extension mechanisms, modules and XS, specifically to avoid
604 the need to keep changing the Perl interpreter. You can write modules
605 that export functions, you can give those functions prototypes so they
606 can be called like built-in functions, you can even write XS code to
607 mess with the runtime data structures of the Perl interpreter if you
608 want to implement really complicated things.
610 Whenever possible, new features should be prototyped in a CPAN module
611 before they will be considered for the core.
613 =head3 Is the feature generic enough?
615 Is this something that only the submitter wants added to the language,
616 or is it broadly useful? Sometimes, instead of adding a feature with a
617 tight focus, the porters might decide to wait until someone implements
618 the more generalized feature.
620 =head3 Does it potentially introduce new bugs?
622 Radical rewrites of large chunks of the Perl interpreter have the
623 potential to introduce new bugs.
625 =head3 How big is it?
627 The smaller and more localized the change, the better. Similarly, a
628 series of small patches is greatly preferred over a single large patch.
630 =head3 Does it preclude other desirable features?
632 A patch is likely to be rejected if it closes off future avenues of
633 development. For instance, a patch that placed a true and final
634 interpretation on prototypes is likely to be rejected because there are
635 still options for the future of prototypes that haven't been addressed.
637 =head3 Is the implementation robust?
639 Good patches (tight code, complete, correct) stand more chance of going
640 in. Sloppy or incorrect patches might be placed on the back burner
641 until the pumpking has time to fix, or might be discarded altogether
642 without further notice.
644 =head3 Is the implementation generic enough to be portable?
646 The worst patches make use of system-specific features. It's highly
647 unlikely that non-portable additions to the Perl language will be
650 =head3 Is the implementation tested?
652 Patches which change behaviour (fixing bugs or introducing new
653 features) must include regression tests to verify that everything works
656 Without tests provided by the original author, how can anyone else
657 changing perl in the future be sure that they haven't unwittingly
658 broken the behaviour the patch implements? And without tests, how can
659 the patch's author be confident that his/her hard work put into the
660 patch won't be accidentally thrown away by someone in the future?
662 =head3 Is there enough documentation?
664 Patches without documentation are probably ill-thought out or
665 incomplete. No features can be added or changed without documentation,
666 so submitting a patch for the appropriate pod docs as well as the
667 source code is important.
669 =head3 Is there another way to do it?
671 Larry said "Although the Perl Slogan is I<There's More Than One Way to
672 Do It>, I hesitate to make 10 ways to do something". This is a tricky
673 heuristic to navigate, though--one man's essential addition is another
674 man's pointless cruft.
676 =head3 Does it create too much work?
678 Work for the pumpking, work for Perl programmers, work for module
679 authors, ... Perl is supposed to be easy.
681 =head3 Patches speak louder than words
683 Working code is always preferred to pie-in-the-sky ideas. A patch to
684 add a feature stands a much higher chance of making it to the language
685 than does a random feature request, no matter how fervently argued the
686 request might be. This ties into "Will it be useful?", as the fact that
687 someone took the time to make the patch demonstrates a strong desire
692 The core uses the same testing style as the rest of Perl, a simple
693 "ok/not ok" run through Test::Harness, but there are a few special
696 There are three ways to write a test in the core. L<Test::More>,
697 F<t/test.pl> and ad hoc C<print $test ? "ok 42\n" : "not ok 42\n">. The
698 decision of which to use depends on what part of the test suite you're
699 working on. This is a measure to prevent a high-level failure (such as
700 Config.pm breaking) from causing basic functionality tests to fail.
702 The F<t/test.pl> library provides some of the features of
703 L<Test::More>, but avoids loading most modules and uses as few core
704 features as possible.
706 If you write your own test, use the L<Test Anything
707 Protocol|http://testanything.org>.
711 =item * F<t/base>, F<t/comp> and F<t/opbasic>
713 Since we don't know if require works, or even subroutines, use ad hoc
714 tests for these three. Step carefully to avoid using the feature being
715 tested. Tests in F<t/opbasic>, for instance, have been placed there rather
716 than in F<t/op> because they test functionality which F<t/test.pl> presumes
717 has already been demonstrated to work.
719 =item * F<t/cmd>, F<t/run>, F<t/io> and F<t/op>
721 Now that basic require() and subroutines are tested, you can use the
722 F<t/test.pl> library.
724 You can also use certain libraries like Config conditionally, but be
725 sure to skip the test gracefully if it's not there.
727 =item * Everything else
729 Now that the core of Perl is tested, L<Test::More> can and should be
730 used. You can also use the full suite of core modules in the tests.
734 When you say "make test", Perl uses the F<t/TEST> program to run the
735 test suite (except under Win32 where it uses F<t/harness> instead). All
736 tests are run from the F<t/> directory, B<not> the directory which
737 contains the test. This causes some problems with the tests in F<lib/>,
738 so here's some opportunity for some patching.
740 You must be triply conscious of cross-platform concerns. This usually
741 boils down to using L<File::Spec> and avoiding things like C<fork()>
742 and C<system()> unless absolutely necessary.
744 =head2 Special C<make test> targets
746 There are various special make targets that can be used to test Perl
747 slightly differently than the standard "test" target. Not all them are
748 expected to give a 100% success rate. Many of them have several
749 aliases, and many of them are not available on certain operating
756 This runs some basic sanity tests on the source tree and helps catch
757 basic errors before you submit a patch.
761 Run F<perl> on all core tests (F<t/*> and F<lib/[a-z]*> pragma tests).
763 (Not available on Win32)
767 Run all the tests through L<B::Deparse>. Not all tests will succeed.
769 (Not available on Win32)
771 =item * test.taintwarn
773 Run all tests with the B<-t> command-line switch. Not all tests are
774 expected to succeed (until they're specifically fixed, of course).
776 (Not available on Win32)
780 Run F<miniperl> on F<t/base>, F<t/comp>, F<t/cmd>, F<t/run>, F<t/io>,
781 F<t/op>, F<t/uni> and F<t/mro> tests.
783 =item * test.valgrind check.valgrind utest.valgrind ucheck.valgrind
785 (Only in Linux) Run all the tests using the memory leak + naughty
786 memory access tool "valgrind". The log files will be named
787 F<testname.valgrind>.
789 =item * test.torture torturetest
791 Run all the usual tests and some extra tests. As of Perl 5.8.0, the
792 only extra tests are Abigail's JAPHs, F<t/japh/abigail.t>.
794 You can also run the torture test with F<t/harness> by giving
795 C<-torture> argument to F<t/harness>.
797 =item * utest ucheck test.utf8 check.utf8
799 Run all the tests with -Mutf8. Not all tests will succeed.
801 (Not available on Win32)
803 =item * minitest.utf16 test.utf16
805 Runs the tests with UTF-16 encoded scripts, encoded with different
806 versions of this encoding.
808 C<make utest.utf16> runs the test suite with a combination of C<-utf8>
809 and C<-utf16> arguments to F<t/TEST>.
811 (Not available on Win32)
815 Run the test suite with the F<t/harness> controlling program, instead
816 of F<t/TEST>. F<t/harness> is more sophisticated, and uses the
817 L<Test::Harness> module, thus using this test target supposes that perl
818 mostly works. The main advantage for our purposes is that it prints a
819 detailed summary of failed tests at the end. Also, unlike F<t/TEST>, it
820 doesn't redirect stderr to stdout.
822 Note that under Win32 F<t/harness> is always used instead of F<t/TEST>,
823 so there is no special "test_harness" target.
825 Under Win32's "test" target you may use the TEST_SWITCHES and
826 TEST_FILES environment variables to control the behaviour of
827 F<t/harness>. This means you can say
829 nmake test TEST_FILES="op/*.t"
830 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
832 =item * test-notty test_notty
834 Sets PERL_SKIP_TTY_TEST to true before running normal test.
838 =head2 Parallel tests
840 The core distribution can now run its regression tests in parallel on
841 Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS>
842 in your environment to the number of tests to run in parallel, and run
843 C<make test_harness>. On a Bourne-like shell, this can be done as
845 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
847 An environment variable is used, rather than parallel make itself,
848 because L<TAP::Harness> needs to be able to schedule individual
849 non-conflicting test scripts itself, and there is no standard interface
850 to C<make> utilities to interact with their job schedulers.
852 Note that currently some test scripts may fail when run in parallel
853 (most notably F<ext/IO/t/io_dir.t>). If necessary, run just the failing
854 scripts again sequentially and see if the failures go away.
856 =head2 Running tests by hand
858 You can run part of the test suite by hand by using one of the
859 following commands from the F<t/> directory:
861 ./perl -I../lib TEST list-of-.t-files
865 ./perl -I../lib harness list-of-.t-files
867 (If you don't specify test scripts, the whole test suite will be run.)
869 =head2 Using F<t/harness> for testing
871 If you use C<harness> for testing, you have several command line
872 options available to you. The arguments are as follows, and are in the
873 order that they must appear if used together.
875 harness -v -torture -re=pattern LIST OF FILES TO TEST
876 harness -v -torture -re LIST OF PATTERNS TO MATCH
878 If C<LIST OF FILES TO TEST> is omitted, the file list is obtained from
879 the manifest. The file list may include shell wildcards which will be
886 Run the tests under verbose mode so you can see what tests were run,
891 Run the torture tests as well as the normal set.
895 Filter the file list so that all the test files run match PATTERN. Note
896 that this form is distinct from the B<-re LIST OF PATTERNS> form below
897 in that it allows the file list to be provided as well.
899 =item * -re LIST OF PATTERNS
901 Filter the file list so that all the test files run match
902 /(LIST|OF|PATTERNS)/. Note that with this form the patterns are joined
903 by '|' and you cannot supply a list of files, instead the test files
904 are obtained from the MANIFEST.
908 You can run an individual test by a command similar to
910 ./perl -I../lib path/to/foo.t
912 except that the harnesses set up some environment variables that may
913 affect the execution of the test:
919 indicates that we're running this test as part of the perl core test
920 suite. This is useful for modules that have a dual life on CPAN.
922 =item * PERL_DESTRUCT_LEVEL=2
924 is set to 2 if it isn't set already (see
925 L<perlhacktips/PERL_DESTRUCT_LEVEL>).
929 (used only by F<t/TEST>) if set, overrides the path to the perl
930 executable that should be used to run the tests (the default being
933 =item * PERL_SKIP_TTY_TEST
935 if set, tells to skip the tests that need a terminal. It's actually set
936 automatically by the Makefile, but can also be forced artificially by
937 running 'make test_notty'.
941 =head3 Other environment variables that may influence tests
945 =item * PERL_TEST_Net_Ping
947 Setting this variable runs all the Net::Ping modules tests, otherwise
948 some tests that interact with the outside world are skipped. See
951 =item * PERL_TEST_NOVREXX
953 Setting this variable skips the vrexx.t tests for OS2::REXX.
955 =item * PERL_TEST_NUMCONVERTS
957 This sets a variable in op/numconvert.t.
959 =item * PERL_TEST_MEMORY
961 Setting this variable includes the tests in F<t/bigmem/>. This should
962 be set to the number of gigabytes of memory available for testing,
963 eg. C<PERL_TEST_MEMORY=4> indicates that tests that require 4GiB of
964 available memory can be run safely.
968 See also the documentation for the Test and Test::Harness modules, for
969 more environment variables that affect testing.
971 =head1 MORE READING FOR GUTS HACKERS
973 To hack on the Perl guts, you'll need to read the following things:
977 =item * L<perlsource>
979 An overview of the Perl source tree. This will help you find the files
982 =item * L<perlinterp>
984 An overview of the Perl interpreter source code and some details on how
985 Perl does what it does.
987 =item * L<perlhacktut>
989 This document walks through the creation of a small patch to Perl's C
990 code. If you're just getting started with Perl core hacking, this will
991 help you understand how it works.
993 =item * L<perlhacktips>
995 More details on hacking the Perl core. This document focuses on lower
996 level details such as how to write tests, compilation issues,
997 portability, debugging, etc.
999 If you plan on doing serious C hacking, make sure to read this.
1003 This is of paramount importance, since it's the documentation of what
1004 goes where in the Perl source. Read it over a couple of times and it
1005 might start to make sense - don't worry if it doesn't yet, because the
1006 best way to study it is to read it in conjunction with poking at Perl
1007 source, and we'll do that later on.
1009 Gisle Aas's "illustrated perlguts", also known as I<illguts>, has very
1012 L<http://search.cpan.org/dist/illguts/>
1014 =item * L<perlxstut> and L<perlxs>
1016 A working knowledge of XSUB programming is incredibly useful for core
1017 hacking; XSUBs use techniques drawn from the PP code, the portion of
1018 the guts that actually executes a Perl program. It's a lot gentler to
1019 learn those techniques from simple examples and explanation than from
1024 The documentation for the Perl API explains what some of the internal
1025 functions do, as well as the many macros used in the source.
1027 =item * F<Porting/pumpkin.pod>
1029 This is a collection of words of wisdom for a Perl porter; some of it
1030 is only useful to the pumpkin holder, but most of it applies to anyone
1031 wanting to go about Perl development.
1035 =head1 CPAN TESTERS AND PERL SMOKERS
1037 The CPAN testers ( http://testers.cpan.org/ ) are a group of volunteers
1038 who test CPAN modules on a variety of platforms.
1040 Perl Smokers ( http://www.nntp.perl.org/group/perl.daily-build/ and
1041 http://www.nntp.perl.org/group/perl.daily-build.reports/ )
1042 automatically test Perl source releases on platforms with various
1045 Both efforts welcome volunteers. In order to get involved in smoke
1046 testing of the perl itself visit
1047 L<http://search.cpan.org/dist/Test-Smoke/>. In order to start smoke
1048 testing CPAN modules visit
1049 L<http://search.cpan.org/dist/CPANPLUS-YACSmoke/> or
1050 L<http://search.cpan.org/dist/minismokebox/> or
1051 L<http://search.cpan.org/dist/CPAN-Reporter/>.
1055 If you've read all the documentation in the document and the ones
1056 listed above, you're more than ready to hack on Perl.
1058 Here's some more recommendations
1064 Subscribe to perl5-porters, follow the patches and try and understand
1065 them; don't be afraid to ask if there's a portion you're not clear on -
1066 who knows, you may unearth a bug in the patch...
1070 Do read the README associated with your operating system, e.g.
1071 README.aix on the IBM AIX OS. Don't hesitate to supply patches to that
1072 README if you find anything missing or changed over a new OS release.
1076 Find an area of Perl that seems interesting to you, and see if you can
1077 work out how it works. Scan through the source, and step over it in the
1078 debugger. Play, poke, investigate, fiddle! You'll probably get to
1079 understand not just your chosen area but a much wider range of
1080 F<perl>'s activity as well, and probably sooner than you'd think.
1084 =head2 "The Road goes ever on and on, down from the door where it began."
1086 If you can do these things, you've started on the long road to Perl
1087 porting. Thanks for wanting to help make Perl better - and happy
1090 =head2 Metaphoric Quotations
1092 If you recognized the quote about the Road above, you're in luck.
1094 Most software projects begin each file with a literal description of
1095 each file's purpose. Perl instead begins each with a literary allusion
1096 to that file's purpose.
1098 Like chapters in many books, all top-level Perl source files (along
1099 with a few others here and there) begin with an epigrammatic
1100 inscription that alludes, indirectly and metaphorically, to the
1101 material you're about to read.
1103 Quotations are taken from writings of J.R.R. Tolkien pertaining to his
1104 Legendarium, almost always from I<The Lord of the Rings>. Chapters and
1105 page numbers are given using the following editions:
1111 I<The Hobbit>, by J.R.R. Tolkien. The hardcover, 70th-anniversary
1112 edition of 2007 was used, published in the UK by Harper Collins
1113 Publishers and in the US by the Houghton Mifflin Company.
1117 I<The Lord of the Rings>, by J.R.R. Tolkien. The hardcover,
1118 50th-anniversary edition of 2004 was used, published in the UK by
1119 Harper Collins Publishers and in the US by the Houghton Mifflin
1124 I<The Lays of Beleriand>, by J.R.R. Tolkien and published posthumously
1125 by his son and literary executor, C.J.R. Tolkien, being the 3rd of the
1126 12 volumes in Christopher's mammoth I<History of Middle Earth>. Page
1127 numbers derive from the hardcover edition, first published in 1983 by
1128 George Allen & Unwin; no page numbers changed for the special 3-volume
1129 omnibus edition of 2002 or the various trade-paper editions, all again
1130 now by Harper Collins or Houghton Mifflin.
1134 Other JRRT books fair game for quotes would thus include I<The
1135 Adventures of Tom Bombadil>, I<The Silmarillion>, I<Unfinished Tales>,
1136 and I<The Tale of the Children of Hurin>, all but the first
1137 posthumously assembled by CJRT. But I<The Lord of the Rings> itself is
1138 perfectly fine and probably best to quote from, provided you can find a
1139 suitable quote there.
1141 So if you were to supply a new, complete, top-level source file to add
1142 to Perl, you should conform to this peculiar practice by yourself
1143 selecting an appropriate quotation from Tolkien, retaining the original
1144 spelling and punctuation and using the same format the rest of the
1145 quotes are in. Indirect and oblique is just fine; remember, it's a
1146 metaphor, so being meta is, after all, what it's for.
1150 This document was originally written by Nathan Torkington, and is
1151 maintained by the perl5-porters mailing list.