3 This document is in Pod format. To read this, use a Pod formatter,
4 like "perldoc perlpod".
7 X<POD> X<plain old documentation>
9 perlpod - the Plain Old Documentation format
13 Pod is a simple-to-use markup language used for writing documentation
14 for Perl, Perl programs, and Perl modules.
16 Translators are available for converting Pod to various formats
17 like plain text, HTML, man pages, and more.
19 Pod markup consists of three basic kinds of paragraphs:
20 L<ordinary|/"Ordinary Paragraph">,
21 L<verbatim|/"Verbatim Paragraph">, and
22 L<command|/"Command Paragraph">.
25 =head2 Ordinary Paragraph
26 X<POD, ordinary paragraph>
28 Most paragraphs in your documentation will be ordinary blocks
29 of text, like this one. You can simply type in your text without
30 any markup whatsoever, and with just a blank line before and
31 after. When it gets formatted, it will undergo minimal formatting,
32 like being rewrapped, probably put into a proportionally spaced
33 font, and maybe even justified.
35 You can use formatting codes in ordinary paragraphs, for B<bold>,
36 I<italic>, C<code-style>, L<hyperlinks|perlfaq>, and more. Such
37 codes are explained in the "L<Formatting Codes|/"Formatting Codes">"
41 =head2 Verbatim Paragraph
42 X<POD, verbatim paragraph> X<verbatim>
44 Verbatim paragraphs are usually used for presenting a codeblock or
45 other text which does not require any special parsing or formatting,
46 and which shouldn't be wrapped.
48 A verbatim paragraph is distinguished by having its first character
49 be a space or a tab. (And commonly, all its lines begin with spaces
50 and/or tabs.) It should be reproduced exactly, with tabs assumed to
51 be on 8-column boundaries. There are no special formatting codes,
52 so you can't italicize or anything like that. A \ means \, and
56 =head2 Command Paragraph
59 A command paragraph is used for special treatment of whole chunks
60 of text, usually as headings or parts of lists.
62 All command paragraphs (which are typically only one line long) start
63 with "=", followed by an identifier, followed by arbitrary text that
64 the command can use however it pleases. Currently recognized commands
81 To explain them each in detail:
85 =item C<=head1 I<Heading Text>>
86 X<=head1> X<=head2> X<=head3> X<=head4>
87 X<head1> X<head2> X<head3> X<head4>
89 =item C<=head2 I<Heading Text>>
91 =item C<=head3 I<Heading Text>>
93 =item C<=head4 I<Heading Text>>
95 Head1 through head4 produce headings, head1 being the highest
96 level. The text in the rest of this paragraph is the content of the
99 =head2 Object Attributes
101 The text "Object Attributes" comprises the heading there.
102 The text in these heading commands can use formatting codes, as seen here:
104 =head2 Possible Values for C<$/>
106 Such commands are explained in the
107 "L<Formatting Codes|/"Formatting Codes">" section, below.
109 =item C<=over I<indentlevel>>
110 X<=over> X<=item> X<=back> X<over> X<item> X<back>
112 =item C<=item I<stuff...>>
116 Item, over, and back require a little more explanation: "=over" starts
117 a region specifically for the generation of a list using "=item"
118 commands, or for indenting (groups of) normal paragraphs. At the end
119 of your list, use "=back" to end it. The I<indentlevel> option to
120 "=over" indicates how far over to indent, generally in ems (where
121 one em is the width of an "M" in the document's base font) or roughly
122 comparable units; if there is no I<indentlevel> option, it defaults
123 to four. (And some formatters may just ignore whatever I<indentlevel>
124 you provide.) In the I<stuff> in C<=item I<stuff...>>, you may
125 use formatting codes, as seen here:
127 =item Using C<$|> to Control Buffering
129 Such commands are explained in the
130 "L<Formatting Codes|/"Formatting Codes">" section, below.
132 Note also that there are some basic rules to using "=over" ...
139 Don't use "=item"s outside of an "=over" ... "=back" region.
143 The first thing after the "=over" command should be an "=item", unless
144 there aren't going to be any items at all in this "=over" ... "=back"
149 Don't put "=headI<n>" commands inside an "=over" ... "=back" region.
153 And perhaps most importantly, keep the items consistent: either use
154 "=item *" for all of them, to produce bullets; or use "=item 1.",
155 "=item 2.", etc., to produce numbered lists; or use "=item foo",
156 "=item bar", etc.--namely, things that look nothing like bullets or
159 If you start with bullets or numbers, stick with them, as
160 formatters use the first "=item" type to decide how to format the
168 To end a Pod block, use a blank line,
169 then a line beginning with "=cut", and a blank
170 line after it. This lets Perl (and the Pod formatter) know that
171 this is where Perl code is resuming. (The blank line before the "=cut"
172 is not technically necessary, but many older Pod processors require it.)
177 The "=pod" command by itself doesn't do much of anything, but it
178 signals to Perl (and Pod formatters) that a Pod block starts here. A
179 Pod block starts with I<any> command paragraph, so a "=pod" command is
180 usually used just when you want to start a Pod block with an ordinary
181 paragraph or a verbatim paragraph. For example:
185 This function does stuff.
195 Remember to check its return value, as in:
197 stuff() || die "Couldn't do stuff!";
201 =item C<=begin I<formatname>>
202 X<=begin> X<=end> X<=for> X<begin> X<end> X<for>
204 =item C<=end I<formatname>>
206 =item C<=for I<formatname> I<text...>>
208 For, begin, and end will let you have regions of text/code/data that
209 are not generally interpreted as normal Pod text, but are passed
210 directly to particular formatters, or are otherwise special. A
211 formatter that can use that format will use the region, otherwise it
212 will be completely ignored.
214 A command "=begin I<formatname>", some paragraphs, and a
215 command "=end I<formatname>", mean that the text/data in between
216 is meant for formatters that understand the special format
217 called I<formatname>. For example,
221 <hr> <img src="thang.png">
222 <p> This is a raw HTML paragraph </p>
226 The command "=for I<formatname> I<text...>"
227 specifies that the remainder of just this paragraph (starting
228 right after I<formatname>) is in that special format.
230 =for html <hr> <img src="thang.png">
231 <p> This is a raw HTML paragraph </p>
233 This means the same thing as the above "=begin html" ... "=end html"
236 That is, with "=for", you can have only one paragraph's worth
237 of text (i.e., the text in "=foo targetname text..."), but with
238 "=begin targetname" ... "=end targetname", you can have any amount
239 of stuff in between. (Note that there still must be a blank line
240 after the "=begin" command and a blank line before the "=end"
243 Here are some examples of how to use these:
247 <br>Figure 1.<br><IMG SRC="figure1.png"><br>
262 Some format names that formatters currently are known to accept
263 include "roff", "man", "latex", "tex", "text", and "html". (Some
264 formatters will treat some of these as synonyms.)
266 A format name of "comment" is common for just making notes (presumably
267 to yourself) that won't appear in any formatted version of the Pod
271 Make sure that all the available options are documented!
273 Some I<formatnames> will require a leading colon (as in
274 C<"=for :formatname">, or
275 C<"=begin :formatname" ... "=end :formatname">),
276 to signal that the text is not raw data, but instead I<is> Pod text
277 (i.e., possibly containing formatting codes) that's just not for
278 normal formatting (e.g., may not be a normal-use paragraph, but might
279 be for formatting as a footnote).
281 =item C<=encoding I<encodingname>>
282 X<=encoding> X<encoding>
284 This command is used for declaring the encoding of a document. Most
285 users won't need this; but if your encoding isn't US-ASCII or Latin-1,
286 then put a C<=encoding I<encodingname>> command early in the document so
287 that pod formatters will know how to decode the document. For
288 I<encodingname>, use a name recognized by the L<Encode::Supported>
301 C<=encoding> affects the whole document, and must occur only once.
303 And don't forget, when using any other command, that the command lasts up
304 until the end of its I<paragraph>, not its line. So in the
305 examples below, you can see that every command needs the blank
306 line after it, to end its paragraph.
308 Some examples of lists include:
326 Description of Foo function
330 Description of Bar function
335 =head2 Formatting Codes
336 X<POD, formatting code> X<formatting code>
337 X<POD, interior sequence> X<interior sequence>
339 In ordinary paragraphs and in some command paragraphs, various
340 formatting codes (a.k.a. "interior sequences") can be used:
343 "interior sequences" is such an opaque term.
344 Prefer "formatting codes" instead.
348 =item C<IE<lt>textE<gt>> -- italic text
349 X<I> X<< IZ<><> >> X<POD, formatting code, italic> X<italic>
351 Used for emphasis ("C<be IE<lt>careful!E<gt>>") and parameters
352 ("C<redo IE<lt>LABELE<gt>>")
354 =item C<BE<lt>textE<gt>> -- bold text
355 X<B> X<< BZ<><> >> X<POD, formatting code, bold> X<bold>
357 Used for switches ("C<perl's BE<lt>-nE<gt> switch>"), programs
358 ("C<some systems provide a BE<lt>chfnE<gt> for that>"),
359 emphasis ("C<be BE<lt>careful!E<gt>>"), and so on
360 ("C<and that feature is known as BE<lt>autovivificationE<gt>>").
362 =item C<CE<lt>codeE<gt>> -- code text
363 X<C> X<< CZ<><> >> X<POD, formatting code, code> X<code>
365 Renders code in a typewriter font, or gives some other indication that
366 this represents program text ("C<CE<lt>gmtime($^T)E<gt>>") or some other
367 form of computerese ("C<CE<lt>drwxr-xr-xE<gt>>").
369 =item C<LE<lt>nameE<gt>> -- a hyperlink
370 X<L> X<< LZ<><> >> X<POD, formatting code, hyperlink> X<hyperlink>
372 There are various syntaxes, listed below. In the syntaxes given,
373 C<text>, C<name>, and C<section> cannot contain the characters
374 '/' and '|'; and any '<' or '>' should be matched.
382 Link to a Perl manual page (e.g., C<LE<lt>Net::PingE<gt>>). Note
383 that C<name> should not contain spaces. This syntax
384 is also occasionally used for references to Unix man pages, as in
385 C<LE<lt>crontab(5)E<gt>>.
389 C<LE<lt>name/"sec"E<gt>> or C<LE<lt>name/secE<gt>>
391 Link to a section in other manual page. E.g.,
392 C<LE<lt>perlsyn/"For Loops"E<gt>>
396 C<LE<lt>/"sec"E<gt>> or C<LE<lt>/secE<gt>>
398 Link to a section in this manual page. E.g.,
399 C<LE<lt>/"Object Methods"E<gt>>
403 A section is started by the named heading or item. For
404 example, C<LE<lt>perlvar/$.E<gt>> or C<LE<lt>perlvar/"$."E<gt>> both
405 link to the section started by "C<=item $.>" in perlvar. And
406 C<LE<lt>perlsyn/For LoopsE<gt>> or C<LE<lt>perlsyn/"For Loops"E<gt>>
407 both link to the section started by "C<=head2 For Loops>"
410 To control what text is used for display, you
411 use "C<LE<lt>text|...E<gt>>", as in:
417 C<LE<lt>text|nameE<gt>>
419 Link this text to that manual page. E.g.,
420 C<LE<lt>Perl Error Messages|perldiagE<gt>>
424 C<LE<lt>text|name/"sec"E<gt>> or C<LE<lt>text|name/secE<gt>>
426 Link this text to that section in that manual page. E.g.,
427 C<LE<lt>postfix "if"|perlsyn/"Statement Modifiers"E<gt>>
431 C<LE<lt>text|/"sec"E<gt>> or C<LE<lt>text|/secE<gt>>
432 or C<LE<lt>text|"sec"E<gt>>
434 Link this text to that section in this manual page. E.g.,
435 C<LE<lt>the various attributes|/"Member Data"E<gt>>
439 Or you can link to a web page:
445 C<LE<lt>scheme:...E<gt>>
447 C<LE<lt>text|scheme:...E<gt>>
449 Links to an absolute URL. For example, C<LE<lt>http://www.perl.org/E<gt>> or
450 C<LE<lt>The Perl Home Page|http://www.perl.org/E<gt>>.
454 =item C<EE<lt>escapeE<gt>> -- a character escape
455 X<E> X<< EZ<><> >> X<POD, formatting code, escape> X<escape>
457 Very similar to HTML/XML C<&I<foo>;> "entity references":
463 C<EE<lt>ltE<gt>> -- a literal E<lt> (less than)
467 C<EE<lt>gtE<gt>> -- a literal E<gt> (greater than)
471 C<EE<lt>verbarE<gt>> -- a literal | (I<ver>tical I<bar>)
475 C<EE<lt>solE<gt>> -- a literal / (I<sol>idus)
477 The above four are optional except in other formatting codes,
478 notably C<LE<lt>...E<gt>>, and when preceded by a
483 C<EE<lt>htmlnameE<gt>>
485 Some non-numeric HTML entity name, such as C<EE<lt>eacuteE<gt>>,
486 meaning the same thing as C<é> in HTML -- i.e., a lowercase
487 e with an acute (/-shaped) accent.
493 The ASCII/Latin-1/Unicode character with that number. A
494 leading "0x" means that I<number> is hex, as in
495 C<EE<lt>0x201EE<gt>>. A leading "0" means that I<number> is octal,
496 as in C<EE<lt>075E<gt>>. Otherwise I<number> is interpreted as being
497 in decimal, as in C<EE<lt>181E<gt>>.
499 Note that older Pod formatters might not recognize octal or
500 hex numeric escapes, and that many formatters cannot reliably
501 render characters above 255. (Some formatters may even have
502 to use compromised renderings of Latin-1 characters, like
503 rendering C<EE<lt>eacuteE<gt>> as just a plain "e".)
507 =item C<FE<lt>filenameE<gt>> -- used for filenames
508 X<F> X<< FZ<><> >> X<POD, formatting code, filename> X<filename>
510 Typically displayed in italics. Example: "C<FE<lt>.cshrcE<gt>>"
512 =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces
513 X<S> X<< SZ<><> >> X<POD, formatting code, non-breaking space>
514 X<non-breaking space>
516 This means that the words in I<text> should not be broken
517 across lines. Example: S<C<SE<lt>$x ? $y : $zE<gt>>>.
519 =item C<XE<lt>topic nameE<gt>> -- an index entry
520 X<X> X<< XZ<><> >> X<POD, formatting code, index entry> X<index entry>
522 This is ignored by most formatters, but some may use it for building
523 indexes. It always renders as empty-string.
524 Example: C<XE<lt>absolutizing relative URLsE<gt>>
526 =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code
527 X<Z> X<< ZZ<><> >> X<POD, formatting code, null> X<null>
529 This is rarely used. It's one way to get around using an
530 EE<lt>...E<gt> code sometimes. For example, instead of
531 "C<NEE<lt>ltE<gt>3>" (for "NE<lt>3") you could write
532 "C<NZE<lt>E<gt>E<lt>3>" (the "ZE<lt>E<gt>" breaks up the "N" and
533 the "E<lt>" so they can't be considered
534 the part of a (fictitious) "NE<lt>...E<gt>" code).
537 This was formerly explained as a "zero-width character". But it in
538 most parser models, it parses to nothing at all, as opposed to parsing
539 as if it were a E<zwnj> or E<zwj>, which are REAL zero-width characters.
540 So "width" and "character" are exactly the wrong words.
544 Most of the time, you will need only a single set of angle brackets to
545 delimit the beginning and end of formatting codes. However,
546 sometimes you will want to put a real right angle bracket (a
547 greater-than sign, '>') inside of a formatting code. This is particularly
548 common when using a formatting code to provide a different font-type for a
549 snippet of code. As with all things in Perl, there is more than
550 one way to do it. One way is to simply escape the closing bracket
555 This will produce: "C<$a E<lt>=E<gt> $b>"
557 A more readable, and perhaps more "plain" way is to use an alternate
558 set of delimiters that doesn't require a single ">" to be escaped.
559 Doubled angle brackets ("<<" and ">>") may be used I<if and only if there is
560 whitespace right after the opening delimiter and whitespace right
561 before the closing delimiter!> For example, the following will
563 X<POD, formatting code, escaping with multiple brackets>
567 In fact, you can use as many repeated angle-brackets as you like so
568 long as you have the same number of them in the opening and closing
569 delimiters, and make sure that whitespace immediately follows the last
570 '<' of the opening delimiter, and immediately precedes the first '>'
571 of the closing delimiter. (The whitespace is ignored.) So the
572 following will also work:
573 X<POD, formatting code, escaping with multiple brackets>
578 And they all mean exactly the same as this:
582 The multiple-bracket form does not affect the interpretation of the contents of
583 the formatting code, only how it must end. That means that the examples above
584 are also exactly the same as this:
586 C<< $a E<lt>=E<gt> $b >>
588 As a further example, this means that if you wanted to put these bits of
589 code in C<C> (code) style:
591 open(X, ">>thing.dat") || die $!
594 you could do it like so:
596 C<<< open(X, ">>thing.dat") || die $! >>>
599 which is presumably easier to read than the old way:
601 C<open(X, "E<gt>E<gt>thing.dat") || die $!>
604 This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
605 and any other pod2xxx or Pod::Xxxx translators that use
606 Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
611 The intent is simplicity of use, not power of expression. Paragraphs
612 look like paragraphs (block format), so that they stand out
613 visually, and so that I could run them through C<fmt> easily to reformat
614 them (that's F7 in my version of B<vi>, or Esc Q in my version of
615 B<emacs>). I wanted the translator to always leave the C<'> and C<`> and
616 C<"> quotes alone, in verbatim mode, so I could slurp in a
617 working program, shift it over four spaces, and have it print out, er,
618 verbatim. And presumably in a monospace font.
620 The Pod format is not necessarily sufficient for writing a book. Pod
621 is just meant to be an idiot-proof common source for nroff, HTML,
622 TeX, and other markup languages, as used for online
623 documentation. Translators exist for B<pod2text>, B<pod2html>,
624 B<pod2man> (that's for nroff(1) and troff(1)), B<pod2latex>, and
625 B<pod2fm>. Various others are available in CPAN.
628 =head2 Embedding Pods in Perl Modules
631 You can embed Pod documentation in your Perl modules and scripts. Start
632 your documentation with an empty line, a "=head1" command at the
633 beginning, and end it with a "=cut" command and an empty line. The
634 B<perl> executable will ignore the Pod text. You can place a Pod
635 statement where B<perl> expects the beginning of a new statement, but
636 not within a statement, as that would result in an error. See any of
637 the supplied library modules for examples.
639 If you're going to put your Pod at the end of the file, and you're using
640 an C<__END__> or C<__DATA__> cut mark, make sure to put an empty line there
641 before the first Pod command.
647 Time::Local - efficiently compute time from local and GMT time
649 Without that empty line before the "=head1", many translators wouldn't
650 have recognized the "=head1" as starting a Pod block.
652 =head2 Hints for Writing Pod
657 X<podchecker> X<POD, validating>
659 The B<podchecker> command is provided for checking Pod syntax for errors
660 and warnings. For example, it checks for completely blank lines in
661 Pod blocks and for unknown commands and formatting codes. You should
662 still also pass your document through one or more translators and proofread
663 the result, or print out the result and proofread that. Some of the
664 problems found may be bugs in the translators, which you may or may not
669 If you're more familiar with writing in HTML than with writing in Pod, you
670 can try your hand at writing documentation in simple HTML, and converting
671 it to Pod with the experimental L<Pod::HTML2Pod|Pod::HTML2Pod> module,
672 (available in CPAN), and looking at the resulting code. The experimental
673 L<Pod::PXML|Pod::PXML> module in CPAN might also be useful.
677 Many older Pod translators require the lines before every Pod
678 command and after every Pod command (including "=cut"!) to be a blank
679 line. Having something like this:
681 # - - - - - - - - - - - -
682 =item $firecracker->boom()
684 This noisily detonates the firecracker object.
689 ...will make such Pod translators completely fail to see the Pod block
692 Instead, have it like this:
694 # - - - - - - - - - - - -
696 =item $firecracker->boom()
698 This noisily detonates the firecracker object.
707 Some older Pod translators require paragraphs (including command
708 paragraphs like "=head2 Functions") to be separated by I<completely>
709 empty lines. If you have an apparently empty line with some spaces
710 on it, this might not count as a separator for those translators, and
711 that could cause odd formatting.
715 Older translators might add wording around an LE<lt>E<gt> link, so that
716 C<LE<lt>Foo::BarE<gt>> may become "the Foo::Bar manpage", for example.
717 So you shouldn't write things like C<the LE<lt>fooE<gt>
718 documentation>, if you want the translated document to read sensibly.
719 Instead, write C<the LE<lt>Foo::Bar|Foo::BarE<gt> documentation> or
720 C<LE<lt>the Foo::Bar documentation|Foo::BarE<gt>>, to control how the
725 Going past the 70th column in a verbatim block might be ungracefully
726 wrapped by some formatters.
732 L<perlpodspec>, L<perlsyn/"PODs: Embedded Documentation">,
733 L<perlnewmod>, L<perldoc>, L<pod2html>, L<pod2man>, L<podchecker>.
737 Larry Wall, Sean M. Burke