1PERLHACK(1) Perl Programmers Reference Guide PERLHACK(1)
2
6 perlhack - How to hack on Perl
7
9 This document explains how Perl development works. It includes details
10 about the Perl 5 Porters email list, the Perl repository, the Perl bug
11 tracker, patch guidelines, and commentary on Perl development
12 philosophy.
13
15 If you just want to submit a single small patch like a pod fix, a test
16 for a bug, comment fixes, etc., it's easy! Here's how:
17 • Check out the source repository
19 The perl source is in a git repository. You can clone the
21 repository with the following command:
22 % git clone https://github.com/Perl/perl5.git perl
24 • Ensure you're following the latest advice
26 In case the advice in this guide has been updated recently, read
28 the latest version directly from the perl source:
29 % perldoc pod/perlhack.pod
31 • Create a branch for your change
33 Create a branch based on blead to commit your change to, which will
35 later be used to send it to the Perl issue tracker.
36 % git checkout -b mychange
38 • Make your change
40 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
44 different character sets. perlhacktips gives advice on this.
45 • Test your change
47 You can run all the tests with the following commands:
49 % ./Configure -des -Dusedevel
51 % make test
52 Keep hacking until the tests pass.
54 • Commit your change
56 Committing your work will save the change on your local system:
58 % git commit -a -m 'Commit message goes here'
60 Make sure the commit message describes your change in a single
62 sentence. For example, "Fixed spelling errors in perlhack.pod".
63 • Send your change to the Perl issue tracker
65 The next step is to submit your patch to the Perl core ticket
67 system.
68 Create a GitHub fork of the perl5 repository and add it as a
70 remote, if you haven't already, as described in the GitHub
71 documentation at
72 <https://help.github.com/en/articles/working-with-forks>.
73 % git remote add fork git@github.com:MyUser/perl5.git
75 For more information, see "Connecting to GitHub with SSH"
77 <https://docs.github.com/en/free-pro-
78 team@latest/github/authenticating-to-github/connecting-to-github-
79 with-ssh>.
80 If you'd rather use an HTTPS URL for your "git push" see "Cloning
82 with HTTPS URLs" <https://docs.github.com/en/free-pro-
83 team@latest/github/using-git/which-remote-url-should-i-use#cloning-
84 with-https-urls>.
85 % git remote add fork https://github.com/MyUser/perl5.git
87 Then, push your new branch to your fork.
89 % git push -u fork mychange
91 Finally, create a Pull Request on GitHub from your branch to blead
93 as described in the GitHub documentation at
94 <https://help.github.com/en/articles/creating-a-pull-request-from-a-fork>.
95 • Thank you
97 The porters appreciate the time you spent helping to make Perl
99 better. Thank you!
100 • Acknowledgement
102 All contributors are credited (by name and email address) in the
104 AUTHORS file, which is part of the perl distribution, as well as
105 the Git commit history.
106 If you donXt want to be included in the AUTHORS file, just let us
108 know. Otherwise we will take your submission of a patch as
109 permission to credit you in the AUTHORS file.
110 • Next time
112 The next time you wish to make a patch, you need to start from the
114 latest perl in a pristine state. Check you don't have any local
115 changes or added files in your perl check-out which you wish to
116 keep, then run these commands:
117 % git checkout blead
119 % git pull
120 % git reset --hard origin/blead
121 % git clean -dxf
122
124 If you want to report a bug in Perl, or browse existing Perl bugs and
125 patches, use the GitHub issue tracker at
126 <https://github.com/perl/perl5/issues>.
127 Please check the archive of the perl5-porters list (see below) and/or
129 the bug tracking system before submitting a bug report. Often, you'll
130 find that the bug has been reported already.
131 You can log in to the bug tracking system and comment on existing bug
133 reports. If you have additional information regarding an existing bug,
134 please add it. This will help the porters fix the bug.
135
137 The perl5-porters (p5p) mailing list is where the Perl standard
138 distribution is maintained and developed. The people who maintain Perl
139 are also referred to as the "Perl 5 Porters", "p5p" or just the
140 "porters".
141 A searchable archive of the list is available at
143 <https://markmail.org/search/?q=perl5-porters>. There is also an
144 archive at <https://archive.develooper.com/perl5-porters@perl.org/>.
145 perl-changes mailing list
147 The perl5-changes mailing list receives a copy of each patch that gets
148 submitted to the maintenance and development branches of the perl
149 repository. See <https://lists.perl.org/list/perl5-changes.html> for
150 subscription and archive information.
151 #p5p on IRC
153 Many porters are also active on the <irc://irc.perl.org/#p5p> channel.
154 Feel free to join the channel and ask questions about hacking on the
155 Perl core.
156
158 All of Perl's source code is kept centrally in a Git repository at
159 github.com. The repository contains many Perl revisions from Perl 1
160 onwards and all the revisions from Perforce, the previous version
161 control system.
162 For much more detail on using git with the Perl repository, please see
164 perlgit.
165 Read access via Git
167 You will need a copy of Git for your computer. You can fetch a copy of
168 the repository using the git protocol:
169 % git clone git://github.com/Perl/perl5.git perl
171 This clones the repository and makes a local copy in the perl
173 directory.
174 If you cannot use the git protocol for firewall reasons, you can also
176 clone via http:
177 % git clone https://github.com/Perl/perl5.git perl
179 Read access via the web
181 You may access the repository over the web. This allows you to browse
182 the tree, see recent commits, subscribe to repository notifications,
183 search for particular commits and more. You may access it at
184 <https://github.com/Perl/perl5>.
185 Read access via rsync
187 You can also choose to use rsync to get a copy of the current source
188 tree for the bleadperl branch and all maintenance branches:
189 % rsync -avz rsync://perl5.git.perl.org/perl-current .
191 % rsync -avz rsync://perl5.git.perl.org/perl-5.12.x .
192 % rsync -avz rsync://perl5.git.perl.org/perl-5.10.x .
193 % rsync -avz rsync://perl5.git.perl.org/perl-5.8.x .
194 % rsync -avz rsync://perl5.git.perl.org/perl-5.6.x .
195 % rsync -avz rsync://perl5.git.perl.org/perl-5.005xx .
196 (Add the "--delete" option to remove leftover files.)
198 To get a full list of the available sync points:
200 % rsync perl5.git.perl.org::
202 Write access via git
204 If you have a commit bit, please see perlgit for more details on using
205 git.
206
208 If you're planning to do more extensive work than a single small fix,
209 we encourage you to read the documentation below. This will help you
210 focus your work and make your patches easier to incorporate into the
211 Perl source.
212 Submitting patches
214 If you have a small patch to submit, please submit it via the GitHub
215 Pull Request workflow. You may also send patches to the p5p list.
216 Patches are reviewed and discussed on GitHub or the p5p list. Simple,
218 uncontroversial patches will usually be applied without any discussion.
219 When the patch is applied, the ticket will be updated and you will
220 receive email.
221 In other cases, the patch will need more work or discussion. You are
223 encouraged to participate in the discussion and advocate for your
224 patch. Sometimes your patch may get lost in the shuffle. It's
225 appropriate to send a reminder email to p5p if no action has been taken
226 in a month. Please remember that the Perl 5 developers are all
227 volunteers, and be polite.
228 Changes are always applied directly to the main development branch,
230 called "blead". Some patches may be backported to a maintenance
231 branch. If you think your patch is appropriate for the maintenance
232 branch (see "MAINTENANCE BRANCHES" in perlpolicy), please explain why
233 when you submit it.
234 Getting your patch accepted
236 If you are submitting a code patch there are several things that you
237 can do to help the Perl 5 Porters accept your patch.
238 Patch style
240 Using the GitHub Pull Request workflow, your patch will automatically
242 be available in a suitable format. If you wish to submit a patch to
243 the p5p list for review, make sure to create it appropriately.
244 If you used git to check out the Perl source, then using "git
246 format-patch" will produce a patch in a style suitable for Perl. The
247 "format-patch" command produces one patch file for each commit you
248 made. If you prefer to send a single patch for all commits, you can
249 use "git diff".
250 % git checkout blead
252 % git pull
253 % git diff blead my-branch-name
254 This produces a patch based on the difference between blead and your
256 current branch. It's important to make sure that blead is up to date
257 before producing the diff, that's why we call "git pull" first.
258 We strongly recommend that you use git if possible. It will make your
260 life easier, and ours as well.
261 However, if you're not using git, you can still produce a suitable
263 patch. You'll need a pristine copy of the Perl source to diff against.
264 The porters prefer unified diffs. Using GNU "diff", you can produce a
265 diff like this:
266 % diff -Npurd perl.pristine perl.mine
268 Make sure that you "make realclean" in your copy of Perl to remove any
270 build artifacts, or you may get a confusing result.
271 Commit message
273 As you craft each patch you intend to submit to the Perl core, it's
275 important to write a good commit message. This is especially important
276 if your submission will consist of a series of commits.
277 The first line of the commit message should be a short description
279 without a period. It should be no longer than the subject line of an
280 email, 50 characters being a good rule of thumb.
281 A lot of Git tools (Gitweb, GitHub, git log --pretty=oneline, ...) will
283 only display the first line (cut off at 50 characters) when presenting
284 commit summaries.
285 The commit message should include a description of the problem that the
287 patch corrects or new functionality that the patch adds.
288 As a general rule of thumb, your commit message should help a
290 programmer who knows the Perl core quickly understand what you were
291 trying to do, how you were trying to do it, and why the change matters
292 to Perl.
293 • Why
295 Your commit message should describe why the change you are making
297 is important. When someone looks at your change in six months or
298 six years, your intent should be clear.
299 If you're deprecating a feature with the intent of later
301 simplifying another bit of code, say so. If you're fixing a
302 performance problem or adding a new feature to support some other
303 bit of the core, mention that.
304 • What
306 Your commit message should describe what part of the Perl core
308 you're changing and what you expect your patch to do.
309 • How
311 While it's not necessary for documentation changes, new tests or
313 trivial patches, it's often worth explaining how your change works.
314 Even if it's clear to you today, it may not be clear to a porter
315 next month or next year.
316 A commit message isn't intended to take the place of comments in your
318 code. Commit messages should describe the change you made, while code
319 comments should describe the current state of the code.
320 If you've just implemented a new feature, complete with doc, tests and
322 well-commented code, a brief commit message will often suffice. If,
323 however, you've just changed a single character deep in the parser or
324 lexer, you might need to write a small novel to ensure that future
325 readers understand what you did and why you did it.
326 Comments, Comments, Comments
328 Be sure to adequately comment your code. While commenting every line
330 is unnecessary, anything that takes advantage of side effects of
331 operators, that creates changes that will be felt outside of the
332 function being patched, or that others may find confusing should be
333 documented. If you are going to err, it is better to err on the side
334 of adding too many comments than too few.
335 The best comments explain why the code does what it does, not what it
337 does.
338 Style
340 In general, please follow the particular style of the code you are
342 patching.
343 In particular, follow these general guidelines for patching Perl
345 sources:
346 • 4-wide indents for code, 2-wide indents for nested CPP "#define"s,
348 with 8-wide tabstops.
349 • Use spaces for indentation, not tab characters.
351 The codebase is a mixture of tabs and spaces for indentation, and
353 we are moving to spaces only. Converting lines you're patching
354 from 8-wide tabs to spaces will help this migration.
355 • Try hard not to exceed 79-columns
357 • ANSI C prototypes
359 • Uncuddled elses and "K&R" style for indenting control constructs
361 • No C++ style (//) comments
363 • Mark places that need to be revisited with XXX (and revisit often!)
365 • Opening brace lines up with "if" when conditional spans multiple
367 lines; should be at end-of-line otherwise
368 • In function definitions, name starts in column 0 (return value-type
370 is on previous line)
371 • Single space after keywords that are followed by parens, no space
373 between function name and following paren
374 • Avoid assignments in conditionals, but if they're unavoidable, use
376 extra paren, e.g. "if (a && (b = c)) ..."
377 • "return foo;" rather than "return(foo);"
379 • "if (!foo) ..." rather than "if (foo == FALSE) ..." etc.
381 • Do not declare variables using "register". It may be
383 counterproductive with modern compilers, and is deprecated in C++,
384 under which the Perl source is regularly compiled.
385 • In-line functions that are in headers that are accessible to XS
387 code need to be able to compile without warnings with commonly used
388 extra compilation flags, such as gcc's "-Wswitch-default" which
389 warns whenever a switch statement does not have a "default" case.
390 The use of these extra flags is to catch potential problems in
391 legal C code, and is often used by Perl aggregators, such as Linux
392 distributors.
393 Test suite
395 If your patch changes code (rather than just changing documentation),
397 you should also include one or more test cases which illustrate the bug
398 you're fixing or validate the new functionality you're adding. In
399 general, you should update an existing test file rather than create a
400 new one.
401 Your test suite additions should generally follow these guidelines
403 (courtesy of Gurusamy Sarathy <gsar@activestate.com>):
404 • Know what you're testing. Read the docs, and the source.
406 • Tend to fail, not succeed.
408 • Interpret results strictly.
410 • Use unrelated features (this will flush out bizarre interactions).
412 • Use non-standard idioms (otherwise you are not testing TIMTOWTDI).
414 • Avoid using hardcoded test numbers whenever possible (the
416 EXPECTED/GOT found in t/op/tie.t is much more maintainable, and
417 gives better failure reports).
418 • Give meaningful error messages when a test fails.
420 • Avoid using qx// and system() unless you are testing for them. If
422 you do use them, make sure that you cover _all_ perl platforms.
423 • Unlink any temporary files you create.
425 • Promote unforeseen warnings to errors with $SIG{__WARN__}.
427 • Be sure to use the libraries and modules shipped with the version
429 being tested, not those that were already installed.
430 • Add comments to the code explaining what you are testing for.
432 • Make updating the '1..42' string unnecessary. Or make sure that
434 you update it.
435 • Test _all_ behaviors of a given operator, library, or function.
437 Test all optional arguments.
439 Test return values in various contexts (boolean, scalar, list,
441 lvalue).
442 Use both global and lexical variables.
444 Don't forget the exceptional, pathological cases.
446 Patching a core module
448 This works just like patching anything else, with one extra
449 consideration.
450 Modules in the cpan/ directory of the source tree are maintained
452 outside of the Perl core. When the author updates the module, the
453 updates are simply copied into the core. See that module's
454 documentation or its listing on <https://metacpan.org/> for more
455 information on reporting bugs and submitting patches.
456 In most cases, patches to modules in cpan/ should be sent upstream and
458 should not be applied to the Perl core individually. If a patch to a
459 file in cpan/ absolutely cannot wait for the fix to be made upstream,
460 released to CPAN and copied to blead, you must add (or update) a
461 "CUSTOMIZED" entry in the "Porting/Maintainers.pl" file to flag that a
462 local modification has been made. See "Porting/Maintainers.pl" for
463 more details.
464 In contrast, modules in the dist/ directory are maintained in the core.
466 Updating perldelta
468 For changes significant enough to warrant a pod/perldelta.pod entry,
469 the porters will greatly appreciate it if you submit a delta entry
470 along with your actual change. Significant changes include, but are
471 not limited to:
472 • Adding, deprecating, or removing core features
474 • Adding, deprecating, removing, or upgrading core or dual-life
476 modules
477 • Adding new core tests
479 • Fixing security issues and user-visible bugs in the core
481 • Changes that might break existing code, either on the perl or C
483 level
484 • Significant performance improvements
486 • Adding, removing, or significantly changing documentation in the
488 pod/ directory
489 • Important platform-specific changes
491 Please make sure you add the perldelta entry to the right section
493 within pod/perldelta.pod. More information on how to write good
494 perldelta entries is available in the "Style" section of
495 Porting/how_to_write_a_perldelta.pod.
496 What makes for a good patch?
498 New features and extensions to the language can be contentious. There
499 is no specific set of criteria which determine what features get added,
500 but here are some questions to consider when developing a patch:
501 Does the concept match the general goals of Perl?
503 Our goals include, but are not limited to:
505 1. Keep it fast, simple, and useful.
507 2. Keep features/concepts as orthogonal as possible.
509 3. No arbitrary limits (platforms, data sizes, cultures).
511 4. Keep it open and exciting to use/patch/advocate Perl everywhere.
513 5. Either assimilate new technologies, or build bridges to them.
515 Where is the implementation?
517 All the talk in the world is useless without an implementation. In
519 almost every case, the person or people who argue for a new feature
520 will be expected to be the ones who implement it. Porters capable of
521 coding new features have their own agendas, and are not available to
522 implement your (possibly good) idea.
523 Backwards compatibility
525 It's a cardinal sin to break existing Perl programs. New warnings can
527 be contentious--some say that a program that emits warnings is not
528 broken, while others say it is. Adding keywords has the potential to
529 break programs, changing the meaning of existing token sequences or
530 functions might break programs.
531 The Perl 5 core includes mechanisms to help porters make backwards
533 incompatible changes more compatible such as the feature and deprecate
534 modules. Please use them when appropriate.
535 Could it be a module instead?
537 Perl 5 has extension mechanisms, modules and XS, specifically to avoid
539 the need to keep changing the Perl interpreter. You can write modules
540 that export functions, you can give those functions prototypes so they
541 can be called like built-in functions, you can even write XS code to
542 mess with the runtime data structures of the Perl interpreter if you
543 want to implement really complicated things.
544 Whenever possible, new features should be prototyped in a CPAN module
546 before they will be considered for the core.
547 Is the feature generic enough?
549 Is this something that only the submitter wants added to the language,
551 or is it broadly useful? Sometimes, instead of adding a feature with a
552 tight focus, the porters might decide to wait until someone implements
553 the more generalized feature.
554 Does it potentially introduce new bugs?
556 Radical rewrites of large chunks of the Perl interpreter have the
558 potential to introduce new bugs.
559 How big is it?
561 The smaller and more localized the change, the better. Similarly, a
563 series of small patches is greatly preferred over a single large patch.
564 Does it preclude other desirable features?
566 A patch is likely to be rejected if it closes off future avenues of
568 development. For instance, a patch that placed a true and final
569 interpretation on prototypes is likely to be rejected because there are
570 still options for the future of prototypes that haven't been addressed.
571 Is the implementation robust?
573 Good patches (tight code, complete, correct) stand more chance of going
575 in. Sloppy or incorrect patches might be placed on the back burner
576 until fixes can be made, or they might be discarded altogether without
577 further notice.
578 Is the implementation generic enough to be portable?
580 The worst patches make use of system-specific features. It's highly
582 unlikely that non-portable additions to the Perl language will be
583 accepted.
584 Is the implementation tested?
586 Patches which change behaviour (fixing bugs or introducing new
588 features) must include regression tests to verify that everything works
589 as expected.
590 Without tests provided by the original author, how can anyone else
592 changing perl in the future be sure that they haven't unwittingly
593 broken the behaviour the patch implements? And without tests, how can
594 the patch's author be confident that his/her hard work put into the
595 patch won't be accidentally thrown away by someone in the future?
596 Is there enough documentation?
598 Patches without documentation are probably ill-thought out or
600 incomplete. No features can be added or changed without documentation,
601 so submitting a patch for the appropriate pod docs as well as the
602 source code is important.
603 Is there another way to do it?
605 Larry said "Although the Perl Slogan is There's More Than One Way to Do
607 It, I hesitate to make 10 ways to do something". This is a tricky
608 heuristic to navigate, though--one man's essential addition is another
609 man's pointless cruft.
610 Does it create too much work?
612 Work for the committers, work for Perl programmers, work for module
614 authors, ... Perl is supposed to be easy.
615 Patches speak louder than words
617 Working code is always preferred to pie-in-the-sky ideas. A patch to
619 add a feature stands a much higher chance of making it to the language
620 than does a random feature request, no matter how fervently argued the
621 request might be. This ties into "Will it be useful?", as the fact
622 that someone took the time to make the patch demonstrates a strong
623 desire for the feature.
624
626 The core uses the same testing style as the rest of Perl, a simple
627 "ok/not ok" run through Test::Harness, but there are a few special
628 considerations.
629 There are three ways to write a test in the core: Test::More, t/test.pl
631 and ad hoc "print $test ? "ok 42\n" : "not ok 42\n"". The decision of
632 which to use depends on what part of the test suite you're working on.
633 This is a measure to prevent a high-level failure (such as Config.pm
634 breaking) from causing basic functionality tests to fail.
635 The t/test.pl library provides some of the features of Test::More, but
637 avoids loading most modules and uses as few core features as possible.
638 If you write your own test, use the Test Anything Protocol
640 <https://testanything.org>.
641 • t/base, t/comp and t/opbasic
643 Since we don't know if "require" works, or even subroutines, use ad
645 hoc tests for these three. Step carefully to avoid using the
646 feature being tested. Tests in t/opbasic, for instance, have been
647 placed there rather than in t/op because they test functionality
648 which t/test.pl presumes has already been demonstrated to work.
649 • All other subdirectories of t/
651 Now that basic require() and subroutines are tested, you can use
653 the t/test.pl library.
654 You can also use certain libraries like Config conditionally, but
656 be sure to skip the test gracefully if it's not there.
657 • Test files not found under t/
659 This category includes .t files underneath directories such as
661 dist, ext and lib. Since the core of Perl has now been tested,
662 Test::More can and now should be used. You can also use the full
663 suite of core modules in the tests. (As noted in "Patching a core
664 module" above, changes to .t files found under cpan/ should be
665 submitted to the upstream maintainers of those modules.)
666 When you say "make test", Perl uses the t/TEST program to run the test
668 suite (except under Win32 where it uses t/harness instead). All tests
669 are run from the t/ directory, not the directory which contains the
670 test. This causes some problems with the tests in lib/, so here's some
671 opportunity for some patching.
672 You must be triply conscious of cross-platform concerns. This usually
674 boils down to using File::Spec, avoiding things like "fork()" and
675 "system()" unless absolutely necessary, and not assuming that a given
676 character has a particular ordinal value (code point) or that its UTF-8
677 representation is composed of particular bytes.
678 There are several functions available to specify characters and code
680 points portably in tests. The always-preloaded functions
681 "utf8::unicode_to_native()" and its inverse "utf8::native_to_unicode()"
682 take code points and translate appropriately. The file
683 t/charset_tools.pl has several functions that can be useful. It has
684 versions of the previous two functions that take strings as inputs --
685 not single numeric code points: "uni_to_native()" and
686 "native_to_uni()". If you must look at the individual bytes comprising
687 a UTF-8 encoded string, "byte_utf8a_to_utf8n()" takes as input a string
688 of those bytes encoded for an ASCII platform, and returns the
689 equivalent string in the native platform. For example,
690 "byte_utf8a_to_utf8n("\xC2\xA0")" returns the byte sequence on the
691 current platform that form the UTF-8 for "U+00A0", since "\xC2\xA0" are
692 the UTF-8 bytes on an ASCII platform for that code point. This
693 function returns "\xC2\xA0" on an ASCII platform, and "\x80\x41" on an
694 EBCDIC 1047 one.
695 But easiest is, if the character is specifiable as a literal, like "A"
697 or "%", to use that; if not so specificable, you can use "\N{}" , if
698 the side effects aren't troublesome. Simply specify all your
699 characters in hex, using "\N{U+ZZ}" instead of "\xZZ". "\N{}" is the
700 Unicode name, and so it always gives you the Unicode character.
701 "\N{U+41}" is the character whose Unicode code point is 0x41, hence is
702 'A' on all platforms. The side effects are:
703 • These select Unicode rules. That means that in double-quotish
705 strings, the string is always converted to UTF-8 to force a Unicode
706 interpretation (you can "utf8::downgrade()" afterwards to convert
707 back to non-UTF8, if possible). In regular expression patterns,
708 the conversion isn't done, but if the character set modifier would
709 otherwise be "/d", it is changed to "/u".
710 • If you use the form "\N{character name}", the charnames module gets
712 automatically loaded. This may not be suitable for the test level
713 you are doing.
714 If you are testing locales (see perllocale), there are helper functions
716 in t/loc_tools.pl to enable you to see what locales there are on the
717 current platform.
718 Special "make test" targets
720 There are various special make targets that can be used to test Perl
721 slightly differently than the standard "test" target. Not all them are
722 expected to give a 100% success rate. Many of them have several
723 aliases, and many of them are not available on certain operating
724 systems.
725 • test_porting
727 This runs some basic sanity tests on the source tree and helps
729 catch basic errors before you submit a patch.
730 • minitest
732 Run miniperl on t/base, t/comp, t/cmd, t/run, t/io, t/op, t/uni and
734 t/mro tests.
735 miniperl is a minimalistic perl built to bootstrap building
737 extensions, utilties, documentation etc. It doesn't support
738 dynamic loading and depending on the point in the build process
739 will only have access to a limited set of core modules. miniperl
740 is not intended for day to day use.
741 • test.valgrind check.valgrind
743 (Only in Linux) Run all the tests using the memory leak + naughty
745 memory access tool "valgrind". The log files will be named
746 testname.valgrind.
747 • test_harness
749 Run the test suite with the t/harness controlling program, instead
751 of t/TEST. t/harness is more sophisticated, and uses the
752 Test::Harness module, thus using this test target supposes that
753 perl mostly works. The main advantage for our purposes is that it
754 prints a detailed summary of failed tests at the end. Also, unlike
755 t/TEST, it doesn't redirect stderr to stdout.
756 Note that under Win32 t/harness is always used instead of t/TEST,
758 so there is no special "test_harness" target.
759 Under Win32's "test" target you may use the TEST_SWITCHES and
761 TEST_FILES environment variables to control the behaviour of
762 t/harness. This means you can say
763 nmake test TEST_FILES="op/*.t"
765 nmake test TEST_SWITCHES="-torture" TEST_FILES="op/*.t"
766 • test-notty test_notty
768 Sets PERL_SKIP_TTY_TEST to true before running normal test.
770 Parallel tests
772 The core distribution can now run its regression tests in parallel on
773 Unix-like and Windows platforms. On Unix, instead of running "make
774 test", set "TEST_JOBS" in your environment to the number of tests to
775 run in parallel, and run "make test_harness". On a Bourne-like shell,
776 this can be done as
777 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
779 An environment variable is used, rather than parallel make itself,
781 because TAP::Harness needs to be able to schedule individual non-
782 conflicting test scripts itself, and there is no standard interface to
783 "make" utilities to interact with their job schedulers.
784 Tests are normally run in a logical order, with the sanity tests first,
786 then the main tests of the Perl core functionality, then the tests for
787 the non-core modules. On many-core systems, this may not use the
788 hardware as effectively as possible. By also specifying
789 TEST_JOBS=19 PERL_TEST_HARNESS_ASAP=1 make -j19 test_harness
791 you signal that you want the tests to finish in wall-clock time as
793 short as possible. After the sanity tests are completed, this causes
794 the remaining ones to be packed into the available cores as tightly as
795 we know how. This has its greatest effect on slower, many-core
796 systems. Throughput was sped up by 20% on an outmoded 24-core system;
797 less on more recent faster ones with fewer cores.
798 Note that the command line above added a "-j" parameter to make, so as
800 to cause parallel compilation. This may or may not work on your
801 platform.
802 Running tests by hand
804 You can run part of the test suite by hand by using one of the
805 following commands from the t/ directory:
806 ./perl -I../lib TEST list-of-.t-files
808 or
810 ./perl -I../lib harness list-of-.t-files
812 (If you don't specify test scripts, the whole test suite will be run.)
814 Using t/harness for testing
816 If you use "harness" for testing, you have several command line options
817 available to you. The arguments are as follows, and are in the order
818 that they must appear if used together.
819 harness -v -torture -re=pattern LIST OF FILES TO TEST
821 harness -v -torture -re LIST OF PATTERNS TO MATCH
822 If "LIST OF FILES TO TEST" is omitted, the file list is obtained from
824 the manifest. The file list may include shell wildcards which will be
825 expanded out.
826 • -v
828 Run the tests under verbose mode so you can see what tests were
830 run, and debug output.
831 • -torture
833 Run the torture tests as well as the normal set.
835 • -re=PATTERN
837 Filter the file list so that all the test files run match PATTERN.
839 Note that this form is distinct from the -re LIST OF PATTERNS form
840 below in that it allows the file list to be provided as well.
841 • -re LIST OF PATTERNS
843 Filter the file list so that all the test files run match
845 /(LIST|OF|PATTERNS)/. Note that with this form the patterns are
846 joined by '|' and you cannot supply a list of files, instead the
847 test files are obtained from the MANIFEST.
848 You can run an individual test by a command similar to
850 ./perl -I../lib path/to/foo.t
852 except that the harnesses set up some environment variables that may
854 affect the execution of the test:
855 • PERL_CORE=1
857 indicates that we're running this test as part of the perl core
859 test suite. This is useful for modules that have a dual life on
860 CPAN.
861 • PERL_DESTRUCT_LEVEL=2
863 is set to 2 if it isn't set already (see "PERL_DESTRUCT_LEVEL" in
865 perlhacktips).
866 • PERL
868 (used only by t/TEST) if set, overrides the path to the perl
870 executable that should be used to run the tests (the default being
871 ./perl).
872 • PERL_SKIP_TTY_TEST
874 if set, tells to skip the tests that need a terminal. It's
876 actually set automatically by the Makefile, but can also be forced
877 artificially by running 'make test_notty'.
878 Other environment variables that may influence tests
880 • PERL_TEST_Net_Ping
882 Setting this variable runs all the Net::Ping modules tests,
884 otherwise some tests that interact with the outside world are
885 skipped. See perl58delta.
886 • PERL_TEST_NOVREXX
888 Setting this variable skips the vrexx.t tests for OS2::REXX.
890 • PERL_TEST_NUMCONVERTS
892 This sets a variable in op/numconvert.t.
894 • PERL_TEST_MEMORY
896 Setting this variable includes the tests in t/bigmem/. This should
898 be set to the number of gigabytes of memory available for testing,
899 eg. "PERL_TEST_MEMORY=4" indicates that tests that require 4GiB of
900 available memory can be run safely.
901 See also the documentation for the Test and Test::Harness modules, for
903 more environment variables that affect testing.
904 Performance testing
906 The file t/perf/benchmarks contains snippets of perl code which are
907 intended to be benchmarked across a range of perls by the
908 Porting/bench.pl tool. If you fix or enhance a performance issue, you
909 may want to add a representative code sample to the file, then run
910 bench.pl against the previous and current perls to see what difference
911 it has made, and whether anything else has slowed down as a
912 consequence.
913 The file t/perf/opcount.t is designed to test whether a particular code
915 snippet has been compiled into an optree containing specified numbers
916 of particular op types. This is good for testing whether optimisations
917 which alter ops, such as converting an "aelem" op into an "aelemfast"
918 op, are really doing that.
919 The files t/perf/speed.t and t/re/speed.t are designed to test things
921 that run thousands of times slower if a particular optimisation is
922 broken (for example, the utf8 length cache on long utf8 strings). Add
923 a test that will take a fraction of a second normally, and minutes
924 otherwise, causing the test file to time out on failure.
925 Building perl at older commits
927 In the course of hacking on the Perl core distribution, you may have
928 occasion to configure, build and test perl at an old commit. Sometimes
929 "make" will fail during this process. If that happens, you may be able
930 to salvage the situation by using the Devel::PatchPerl library from
931 CPAN (not included in the core) to bring the source code at that commit
932 to a buildable state.
933 Here's a real world example, taken from work done to resolve perl
935 #10118 <https://github.com/Perl/perl5/issues/10118>. Use of
936 Porting/bisect.pl had identified commit
937 "ba77e4cc9d1ceebf472c9c5c18b2377ee47062e6" as the commit in which a bug
938 was corrected. To confirm, a P5P developer wanted to configure and
939 build perl at commit "ba77e4c^" (presumably "bad") and then at
940 "ba77e4c" (presumably "good"). Normal configuration and build was
941 attempted:
942 $ sh ./Configure -des -Dusedevel
944 $ make test_prep
945 "make", however, failed with output (excerpted) like this:
947 cc -fstack-protector -L/usr/local/lib -o miniperl \
949 gv.o toke.o perly.o pad.o regcomp.o dump.o util.o \
950 mg.o reentr.o mro.o hv.o av.o run.o pp_hot.o sv.o \
951 pp.o scope.o pp_ctl.o pp_sys.o doop.o doio.o regexec.o \
952 utf8.o taint.o deb.o universal.o globals.o perlio.o \
953 numeric.o mathoms.o locale.o pp_pack.o pp_sort.o \
954 miniperlmain.o opmini.o perlmini.o
955 pp.o: In function `Perl_pp_pow':
956 pp.c:(.text+0x2db9): undefined reference to `pow'
957 ...
958 collect2: error: ld returned 1 exit status
959 makefile:348: recipe for target 'miniperl' failed
960 make: *** [miniperl] Error 1
961 Another P5P contributor recommended installation and use of
963 Devel::PatchPerl for this situation, first to determine the version of
964 perl at the commit in question, then to patch the source code at that
965 point to facilitate a build.
966 $ perl -MDevel::PatchPerl -e \
968 'print Devel::PatchPerl->determine_version("/path/to/sourcecode"), "\n";'
969 5.11.1
970 $ perl -MDevel::PatchPerl -e \
971 'Devel::PatchPerl->patch_source("5.11.1", "/path/to/sourcecode");'
972 Once the source was patched, "./Configure" and "make test_prep" were
974 called and completed successfully, enabling confirmation of the
975 findings in RT #72414.
976
978 To hack on the Perl guts, you'll need to read the following things:
979 • perlsource
981 An overview of the Perl source tree. This will help you find the
983 files you're looking for.
984 • perlinterp
986 An overview of the Perl interpreter source code and some details on
988 how Perl does what it does.
989 • perlhacktut
991 This document walks through the creation of a small patch to Perl's
993 C code. If you're just getting started with Perl core hacking,
994 this will help you understand how it works.
995 • perlhacktips
997 More details on hacking the Perl core. This document focuses on
999 lower level details such as how to write tests, compilation issues,
1000 portability, debugging, etc.
1001 If you plan on doing serious C hacking, make sure to read this.
1003 • perlguts
1005 This is of paramount importance, since it's the documentation of
1007 what goes where in the Perl source. Read it over a couple of times
1008 and it might start to make sense - don't worry if it doesn't yet,
1009 because the best way to study it is to read it in conjunction with
1010 poking at Perl source, and we'll do that later on.
1011 Gisle Aas's "illustrated perlguts", also known as illguts, has very
1013 helpful pictures:
1014 <https://metacpan.org/release/RURBAN/illguts-0.49>
1016 • perlxstut and perlxs
1018 A working knowledge of XSUB programming is incredibly useful for
1020 core hacking; XSUBs use techniques drawn from the PP code, the
1021 portion of the guts that actually executes a Perl program. It's a
1022 lot gentler to learn those techniques from simple examples and
1023 explanation than from the core itself.
1024 • perlapi
1026 The documentation for the Perl API explains what some of the
1028 internal functions do, as well as the many macros used in the
1029 source.
1030 • Porting/pumpkin.pod
1032 This is a collection of words of wisdom for a Perl porter; some of
1034 it is only useful to the pumpkin holders, but most of it applies to
1035 anyone wanting to go about Perl development.
1036
1038 The CPAN testers ( <http://cpantesters.org/> ) are a group of
1039 volunteers who test CPAN modules on a variety of platforms.
1040 Perl Smokers ( <https://www.nntp.perl.org/group/perl.daily-build/> and
1042 <https://www.nntp.perl.org/group/perl.daily-build.reports/> )
1043 automatically test Perl source releases on platforms with various
1044 configurations.
1045 Both efforts welcome volunteers. In order to get involved in smoke
1047 testing of the perl itself visit
1048 <https://metacpan.org/release/Test-Smoke>. In order to start smoke
1049 testing CPAN modules visit
1050 <https://metacpan.org/release/CPANPLUS-YACSmoke> or
1051 <https://metacpan.org/release/minismokebox> or
1052 <https://metacpan.org/release/CPAN-Reporter>.
1053
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.
1057 Here's some more recommendations
1059 • Subscribe to perl5-porters, follow the patches and try and
1061 understand them; don't be afraid to ask if there's a portion you're
1062 not clear on - who knows, you may unearth a bug in the patch...
1063 • 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
1066 that README if you find anything missing or changed over a new OS
1067 release.
1068 • Find an area of Perl that seems interesting to you, and see if you
1070 can work out how it works. Scan through the source, and step over
1071 it in the debugger. Play, poke, investigate, fiddle! You'll
1072 probably get to understand not just your chosen area but a much
1073 wider range of perl's activity as well, and probably sooner than
1074 you'd think.
1075 "The Road goes ever on and on, down from the door where it began."
1077 If you can do these things, you've started on the long road to Perl
1078 porting. Thanks for wanting to help make Perl better - and happy
1079 hacking!
1080 Metaphoric Quotations
1082 If you recognized the quote about the Road above, you're in luck.
1083 Most software projects begin each file with a literal description of
1085 each file's purpose. Perl instead begins each with a literary allusion
1086 to that file's purpose.
1087 Like chapters in many books, all top-level Perl source files (along
1089 with a few others here and there) begin with an epigrammatic
1090 inscription that alludes, indirectly and metaphorically, to the
1091 material you're about to read.
1092 Quotations are taken from writings of J.R.R. Tolkien pertaining to his
1094 Legendarium, almost always from The Lord of the Rings. Chapters and
1095 page numbers are given using the following editions:
1096 • The Hobbit, by J.R.R. Tolkien. The hardcover, 70th-anniversary
1098 edition of 2007 was used, published in the UK by Harper Collins
1099 Publishers and in the US by the Houghton Mifflin Company.
1100 • The Lord of the Rings, by J.R.R. Tolkien. The hardcover,
1102 50th-anniversary edition of 2004 was used, published in the UK by
1103 Harper Collins Publishers and in the US by the Houghton Mifflin
1104 Company.
1105 • The Lays of Beleriand, by J.R.R. Tolkien and published posthumously
1107 by his son and literary executor, C.J.R. Tolkien, being the 3rd of
1108 the 12 volumes in Christopher's mammoth History of Middle Earth.
1109 Page numbers derive from the hardcover edition, first published in
1110 1983 by George Allen & Unwin; no page numbers changed for the
1111 special 3-volume omnibus edition of 2002 or the various trade-paper
1112 editions, all again now by Harper Collins or Houghton Mifflin.
1113 Other JRRT books fair game for quotes would thus include The Adventures
1115 of Tom Bombadil, The Silmarillion, Unfinished Tales, and The Tale of
1116 the Children of Hurin, all but the first posthumously assembled by
1117 CJRT. But The Lord of the Rings itself is perfectly fine and probably
1118 best to quote from, provided you can find a suitable quote there.
1119 So if you were to supply a new, complete, top-level source file to add
1121 to Perl, you should conform to this peculiar practice by yourself
1122 selecting an appropriate quotation from Tolkien, retaining the original
1123 spelling and punctuation and using the same format the rest of the
1124 quotes are in. Indirect and oblique is just fine; remember, it's a
1125 metaphor, so being meta is, after all, what it's for.
1126
1128 This document was originally written by Nathan Torkington, and is
1129 maintained by the perl5-porters mailing list.
1130perl v5.34.1 2022-03-15 PERLHACK(1)