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
80 To explain them each in detail:
84 =item C<=head1 I<Heading Text>>
85 X<=head1> X<=head2> X<=head3> X<=head4>
86 X<head1> X<head2> X<head3> X<head4>
88 =item C<=head2 I<Heading Text>>
90 =item C<=head3 I<Heading Text>>
92 =item C<=head4 I<Heading Text>>
94 Head1 through head4 produce headings, head1 being the highest
95 level. The text in the rest of this paragraph is the content of the
98 =head2 Object Attributes
100 The text "Object Attributes" comprises the heading there. (Note that
101 head3 and head4 are recent additions, not supported in older Pod
102 translators.) The text in these heading commands can use
103 formatting codes, as seen here:
105 =head2 Possible Values for C<$/>
107 Such commands are explained in the
108 "L<Formatting Codes|/"Formatting Codes">" section, below.
110 =item C<=over I<indentlevel>>
111 X<=over> X<=item> X<=back> X<over> X<item> X<back>
113 =item C<=item I<stuff...>>
117 Item, over, and back require a little more explanation: "=over" starts
118 a region specifically for the generation of a list using "=item"
119 commands, or for indenting (groups of) normal paragraphs. At the end
120 of your list, use "=back" to end it. The I<indentlevel> option to
121 "=over" indicates how far over to indent, generally in ems (where
122 one em is the width of an "M" in the document's base font) or roughly
123 comparable units; if there is no I<indentlevel> option, it defaults
124 to four. (And some formatters may just ignore whatever I<indentlevel>
125 you provide.) In the I<stuff> in C<=item I<stuff...>>, you may
126 use formatting codes, as seen here:
128 =item Using C<$|> to Control Buffering
130 Such commands are explained in the
131 "L<Formatting Codes|/"Formatting Codes">" section, below.
133 Note also that there are some basic rules to using "=over" ...
140 Don't use "=item"s outside of an "=over" ... "=back" region.
144 The first thing after the "=over" command should be an "=item", unless
145 there aren't going to be any items at all in this "=over" ... "=back"
150 Don't put "=headI<n>" commands inside an "=over" ... "=back" region.
154 And perhaps most importantly, keep the items consistent: either use
155 "=item *" for all of them, to produce bullets; or use "=item 1.",
156 "=item 2.", etc., to produce numbered lists; or use "=item foo",
157 "=item bar", etc. -- namely, things that look nothing like bullets or
160 If you start with bullets or numbers, stick with them, as
161 formatters use the first "=item" type to decide how to format the
169 To end a Pod block, use a blank line,
170 then a line beginning with "=cut", and a blank
171 line after it. This lets Perl (and the Pod formatter) know that
172 this is where Perl code is resuming. (The blank line before the "=cut"
173 is not technically necessary, but many older Pod processors require it.)
178 The "=pod" command by itself doesn't do much of anything, but it
179 signals to Perl (and Pod formatters) that a Pod block starts here. A
180 Pod block starts with I<any> command paragraph, so a "=pod" command is
181 usually used just when you want to start a Pod block with an ordinary
182 paragraph or a verbatim paragraph. For example:
186 This function does stuff.
196 Remember to check its return value, as in:
198 stuff() || die "Couldn't do stuff!";
202 =item C<=begin I<formatname>>
203 X<=begin> X<=end> X<=for> X<begin> X<end> X<for>
205 =item C<=end I<formatname>>
207 =item C<=for I<formatname> I<text...>>
209 For, begin, and end will let you have regions of text/code/data that
210 are not generally interpreted as normal Pod text, but are passed
211 directly to particular formatters, or are otherwise special. A
212 formatter that can use that format will use the region, otherwise it
213 will be completely ignored.
215 A command "=begin I<formatname>", some paragraphs, and a
216 command "=end I<formatname>", mean that the text/data inbetween
217 is meant for formatters that understand the special format
218 called I<formatname>. For example,
222 <hr> <img src="thang.png">
223 <p> This is a raw HTML paragraph </p>
227 The command "=for I<formatname> I<text...>"
228 specifies that the remainder of just this paragraph (starting
229 right after I<formatname>) is in that special format.
231 =for html <hr> <img src="thang.png">
232 <p> This is a raw HTML paragraph </p>
234 This means the same thing as the above "=begin html" ... "=end html"
237 That is, with "=for", you can have only one paragraph's worth
238 of text (i.e., the text in "=foo targetname text..."), but with
239 "=begin targetname" ... "=end targetname", you can have any amount
240 of stuff inbetween. (Note that there still must be a blank line
241 after the "=begin" command and a blank line before the "=end"
244 Here are some examples of how to use these:
248 <br>Figure 1.<br><IMG SRC="figure1.png"><br>
263 Some format names that formatters currently are known to accept
264 include "roff", "man", "latex", "tex", "text", and "html". (Some
265 formatters will treat some of these as synonyms.)
267 A format name of "comment" is common for just making notes (presumably
268 to yourself) that won't appear in any formatted version of the Pod
272 Make sure that all the available options are documented!
274 Some I<formatnames> will require a leading colon (as in
275 C<"=for :formatname">, or
276 C<"=begin :formatname" ... "=end :formatname">),
277 to signal that the text is not raw data, but instead I<is> Pod text
278 (i.e., possibly containing formatting codes) that's just not for
279 normal formatting (e.g., may not be a normal-use paragraph, but might
280 be for formatting as a footnote).
282 =item C<=encoding I<encodingname>>
283 X<=encoding> X<encoding>
285 This command is used for declaring the encoding of a document. Most
286 users won't need this; but if your encoding isn't US-ASCII or Latin-1,
287 then put a C<=encoding I<encodingname>> command early in the document so
288 that pod formatters will know how to decode the document. For
289 I<encodingname>, use a name recognized by the L<Encode::Supported>
302 And don't forget, when using any command, that the command lasts up
303 until the end of its I<paragraph>, not its line. So in the
304 examples below, you can see that every command needs the blank
305 line after it, to end its paragraph.
307 Some examples of lists include:
325 Description of Foo function
329 Description of Bar function
334 =head2 Formatting Codes
335 X<POD, formatting code> X<formatting code>
336 X<POD, interior sequence> X<interior sequence>
338 In ordinary paragraphs and in some command paragraphs, various
339 formatting codes (a.k.a. "interior sequences") can be used:
342 "interior sequences" is such an opaque term.
343 Prefer "formatting codes" instead.
347 =item C<IE<lt>textE<gt>> -- italic text
348 X<I> X<< IZ<><> >> X<POD, formatting code, italic> X<italic>
350 Used for emphasis ("C<be IE<lt>careful!E<gt>>") and parameters
351 ("C<redo IE<lt>LABELE<gt>>")
353 =item C<BE<lt>textE<gt>> -- bold text
354 X<B> X<< BZ<><> >> X<POD, formatting code, bold> X<bold>
356 Used for switches ("C<perl's BE<lt>-nE<gt> switch>"), programs
357 ("C<some systems provide a BE<lt>chfnE<gt> for that>"),
358 emphasis ("C<be BE<lt>careful!E<gt>>"), and so on
359 ("C<and that feature is known as BE<lt>autovivificationE<gt>>").
361 =item C<CE<lt>codeE<gt>> -- code text
362 X<C> X<< CZ<><> >> X<POD, formatting code, code> X<code>
364 Renders code in a typewriter font, or gives some other indication that
365 this represents program text ("C<CE<lt>gmtime($^T)E<gt>>") or some other
366 form of computerese ("C<CE<lt>drwxr-xr-xE<gt>>").
368 =item C<LE<lt>nameE<gt>> -- a hyperlink
369 X<L> X<< LZ<><> >> X<POD, formatting code, hyperlink> X<hyperlink>
371 There are various syntaxes, listed below. In the syntaxes given,
372 C<text>, C<name>, and C<section> cannot contain the characters
373 '/' and '|'; and any '<' or '>' should be matched.
381 Link to a Perl manual page (e.g., C<LE<lt>Net::PingE<gt>>). Note
382 that C<name> should not contain spaces. This syntax
383 is also occasionally used for references to UNIX man pages, as in
384 C<LE<lt>crontab(5)E<gt>>.
388 C<LE<lt>name/"sec"E<gt>> or C<LE<lt>name/secE<gt>>
390 Link to a section in other manual page. E.g.,
391 C<LE<lt>perlsyn/"For Loops"E<gt>>
395 C<LE<lt>/"sec"E<gt>> or C<LE<lt>/secE<gt>> or C<LE<lt>"sec"E<gt>>
397 Link to a section in this manual page. E.g.,
398 C<LE<lt>/"Object Methods"E<gt>>
402 A section is started by the named heading or item. For
403 example, C<LE<lt>perlvar/$.E<gt>> or C<LE<lt>perlvar/"$."E<gt>> both
404 link to the section started by "C<=item $.>" in perlvar. And
405 C<LE<lt>perlsyn/For LoopsE<gt>> or C<LE<lt>perlsyn/"For Loops"E<gt>>
406 both link to the section started by "C<=head2 For Loops>"
409 To control what text is used for display, you
410 use "C<LE<lt>text|...E<gt>>", as in:
416 C<LE<lt>text|nameE<gt>>
418 Link this text to that manual page. E.g.,
419 C<LE<lt>Perl Error Messages|perldiagE<gt>>
423 C<LE<lt>text|name/"sec"E<gt>> or C<LE<lt>text|name/secE<gt>>
425 Link this text to that section in that manual page. E.g.,
426 C<LE<lt>SWITCH statements|perlsyn/"Basic BLOCKs and Switch
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 Links to an absolute URL. For example,
448 C<LE<lt>http://www.perl.org/E<gt>>. But note
449 that there is no corresponding C<LE<lt>text|scheme:...E<gt>> syntax, for
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. With
559 the Pod formatters that are standard starting with perl5.5.660, doubled
560 angle brackets ("<<" and ">>") may be used I<if and only if there is
561 whitespace right after the opening delimiter and whitespace right
562 before the closing delimiter!> For example, the following will
564 X<POD, formatting code, escaping with multiple brackets>
568 In fact, you can use as many repeated angle-brackets as you like so
569 long as you have the same number of them in the opening and closing
570 delimiters, and make sure that whitespace immediately follows the last
571 '<' of the opening delimiter, and immediately precedes the first '>'
572 of the closing delimiter. (The whitespace is ignored.) So the
573 following will also work:
574 X<POD, formatting code, escaping with multiple brackets>
579 And they all mean exactly the same as this:
583 As a further example, this means that if you wanted to put these bits of
584 code in C<C> (code) style:
586 open(X, ">>thing.dat") || die $!
589 you could do it like so:
591 C<<< open(X, ">>thing.dat") || die $! >>>
594 which is presumably easier to read than the old way:
596 C<open(X, "E<gt>E<gt>thing.dat") || die $!>
599 This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
600 and any other pod2xxx or Pod::Xxxx translators that use
601 Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
606 The intent is simplicity of use, not power of expression. Paragraphs
607 look like paragraphs (block format), so that they stand out
608 visually, and so that I could run them through C<fmt> easily to reformat
609 them (that's F7 in my version of B<vi>, or Esc Q in my version of
610 B<emacs>). I wanted the translator to always leave the C<'> and C<`> and
611 C<"> quotes alone, in verbatim mode, so I could slurp in a
612 working program, shift it over four spaces, and have it print out, er,
613 verbatim. And presumably in a monospace font.
615 The Pod format is not necessarily sufficient for writing a book. Pod
616 is just meant to be an idiot-proof common source for nroff, HTML,
617 TeX, and other markup languages, as used for online
618 documentation. Translators exist for B<pod2text>, B<pod2html>,
619 B<pod2man> (that's for nroff(1) and troff(1)), B<pod2latex>, and
620 B<pod2fm>. Various others are available in CPAN.
623 =head2 Embedding Pods in Perl Modules
626 You can embed Pod documentation in your Perl modules and scripts.
627 Start your documentation with an empty line, a "=head1" command at the
628 beginning, and end it with a "=cut" command and an empty line. Perl
629 will ignore the Pod text. See any of the supplied library modules for
630 examples. If you're going to put your Pod at the end of the file, and
631 you're using an __END__ or __DATA__ cut mark, make sure to put an
632 empty line there before the first Pod command.
638 Time::Local - efficiently compute time from local and GMT time
640 Without that empty line before the "=head1", many translators wouldn't
641 have recognized the "=head1" as starting a Pod block.
643 =head2 Hints for Writing Pod
648 X<podchecker> X<POD, validating>
650 The B<podchecker> command is provided for checking Pod syntax for errors
651 and warnings. For example, it checks for completely blank lines in
652 Pod blocks and for unknown commands and formatting codes. You should
653 still also pass your document through one or more translators and proofread
654 the result, or print out the result and proofread that. Some of the
655 problems found may be bugs in the translators, which you may or may not
660 If you're more familiar with writing in HTML than with writing in Pod, you
661 can try your hand at writing documentation in simple HTML, and converting
662 it to Pod with the experimental L<Pod::HTML2Pod|Pod::HTML2Pod> module,
663 (available in CPAN), and looking at the resulting code. The experimental
664 L<Pod::PXML|Pod::PXML> module in CPAN might also be useful.
668 Many older Pod translators require the lines before every Pod
669 command and after every Pod command (including "=cut"!) to be a blank
670 line. Having something like this:
672 # - - - - - - - - - - - -
673 =item $firecracker->boom()
675 This noisily detonates the firecracker object.
680 ...will make such Pod translators completely fail to see the Pod block
683 Instead, have it like this:
685 # - - - - - - - - - - - -
687 =item $firecracker->boom()
689 This noisily detonates the firecracker object.
698 Some older Pod translators require paragraphs (including command
699 paragraphs like "=head2 Functions") to be separated by I<completely>
700 empty lines. If you have an apparently empty line with some spaces
701 on it, this might not count as a separator for those translators, and
702 that could cause odd formatting.
706 Older translators might add wording around an LE<lt>E<gt> link, so that
707 C<LE<lt>Foo::BarE<gt>> may become "the Foo::Bar manpage", for example.
708 So you shouldn't write things like C<the LE<lt>fooE<gt>
709 documentation>, if you want the translated document to read sensibly
710 -- instead write C<the LE<lt>Foo::Bar|Foo::BarE<gt> documentation> or
711 C<LE<lt>the Foo::Bar documentation|Foo::BarE<gt>>, to control how the
716 Going past the 70th column in a verbatim block might be ungracefully
717 wrapped by some formatters.
723 L<perlpodspec>, L<perlsyn/"PODs: Embedded Documentation">,
724 L<perlnewmod>, L<perldoc>, L<pod2html>, L<pod2man>, L<podchecker>.
728 Larry Wall, Sean M. Burke