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,
286 then put a C<=encoding I<encodingname>> command very 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>
289 module. Some pod formatters may try to guess between a Latin-1 or
291 UTF-8 encoding, but they may guess wrong. It's best to be explicit if
292 you use anything besides strict ASCII. Examples:
304 C<=encoding> affects the whole document, and must occur only once.
308 And don't forget, all commands but C<=encoding> last up
309 until the end of its I<paragraph>, not its line. So in the
310 examples below, you can see that every command needs the blank
311 line after it, to end its paragraph. (And some older Pod translators
312 may require the C<=encoding> line to have a following blank line as
313 well, even though it should be legal to omit.)
315 Some examples of lists include:
333 Description of Foo function
337 Description of Bar function
342 =head2 Formatting Codes
343 X<POD, formatting code> X<formatting code>
344 X<POD, interior sequence> X<interior sequence>
346 In ordinary paragraphs and in some command paragraphs, various
347 formatting codes (a.k.a. "interior sequences") can be used:
350 "interior sequences" is such an opaque term.
351 Prefer "formatting codes" instead.
355 =item C<IE<lt>textE<gt>> -- italic text
356 X<I> X<< IZ<><> >> X<POD, formatting code, italic> X<italic>
358 Used for emphasis ("C<be IE<lt>careful!E<gt>>") and parameters
359 ("C<redo IE<lt>LABELE<gt>>")
361 =item C<BE<lt>textE<gt>> -- bold text
362 X<B> X<< BZ<><> >> X<POD, formatting code, bold> X<bold>
364 Used for switches ("C<perl's BE<lt>-nE<gt> switch>"), programs
365 ("C<some systems provide a BE<lt>chfnE<gt> for that>"),
366 emphasis ("C<be BE<lt>careful!E<gt>>"), and so on
367 ("C<and that feature is known as BE<lt>autovivificationE<gt>>").
369 =item C<CE<lt>codeE<gt>> -- code text
370 X<C> X<< CZ<><> >> X<POD, formatting code, code> X<code>
372 Renders code in a typewriter font, or gives some other indication that
373 this represents program text ("C<CE<lt>gmtime($^T)E<gt>>") or some other
374 form of computerese ("C<CE<lt>drwxr-xr-xE<gt>>").
376 =item C<LE<lt>nameE<gt>> -- a hyperlink
377 X<L> X<< LZ<><> >> X<POD, formatting code, hyperlink> X<hyperlink>
379 There are various syntaxes, listed below. In the syntaxes given,
380 C<text>, C<name>, and C<section> cannot contain the characters
381 '/' and '|'; and any '<' or '>' should be matched.
389 Link to a Perl manual page (e.g., C<LE<lt>Net::PingE<gt>>). Note
390 that C<name> should not contain spaces. This syntax
391 is also occasionally used for references to Unix man pages, as in
392 C<LE<lt>crontab(5)E<gt>>.
396 C<LE<lt>name/"sec"E<gt>> or C<LE<lt>name/secE<gt>>
398 Link to a section in other manual page. E.g.,
399 C<LE<lt>perlsyn/"For Loops"E<gt>>
403 C<LE<lt>/"sec"E<gt>> or C<LE<lt>/secE<gt>>
405 Link to a section in this manual page. E.g.,
406 C<LE<lt>/"Object Methods"E<gt>>
410 A section is started by the named heading or item. For
411 example, C<LE<lt>perlvar/$.E<gt>> or C<LE<lt>perlvar/"$."E<gt>> both
412 link to the section started by "C<=item $.>" in perlvar. And
413 C<LE<lt>perlsyn/For LoopsE<gt>> or C<LE<lt>perlsyn/"For Loops"E<gt>>
414 both link to the section started by "C<=head2 For Loops>"
417 To control what text is used for display, you
418 use "C<LE<lt>text|...E<gt>>", as in:
424 C<LE<lt>text|nameE<gt>>
426 Link this text to that manual page. E.g.,
427 C<LE<lt>Perl Error Messages|perldiagE<gt>>
431 C<LE<lt>text|name/"sec"E<gt>> or C<LE<lt>text|name/secE<gt>>
433 Link this text to that section in that manual page. E.g.,
434 C<LE<lt>postfix "if"|perlsyn/"Statement Modifiers"E<gt>>
438 C<LE<lt>text|/"sec"E<gt>> or C<LE<lt>text|/secE<gt>>
439 or C<LE<lt>text|"sec"E<gt>>
441 Link this text to that section in this manual page. E.g.,
442 C<LE<lt>the various attributes|/"Member Data"E<gt>>
446 Or you can link to a web page:
452 C<LE<lt>scheme:...E<gt>>
454 C<LE<lt>text|scheme:...E<gt>>
456 Links to an absolute URL. For example, C<LE<lt>http://www.perl.org/E<gt>> or
457 C<LE<lt>The Perl Home Page|http://www.perl.org/E<gt>>.
461 =item C<EE<lt>escapeE<gt>> -- a character escape
462 X<E> X<< EZ<><> >> X<POD, formatting code, escape> X<escape>
464 Very similar to HTML/XML C<&I<foo>;> "entity references":
470 C<EE<lt>ltE<gt>> -- a literal E<lt> (less than)
474 C<EE<lt>gtE<gt>> -- a literal E<gt> (greater than)
478 C<EE<lt>verbarE<gt>> -- a literal | (I<ver>tical I<bar>)
482 C<EE<lt>solE<gt>> -- a literal / (I<sol>idus)
484 The above four are optional except in other formatting codes,
485 notably C<LE<lt>...E<gt>>, and when preceded by a
490 C<EE<lt>htmlnameE<gt>>
492 Some non-numeric HTML entity name, such as C<EE<lt>eacuteE<gt>>,
493 meaning the same thing as C<é> in HTML -- i.e., a lowercase
494 e with an acute (/-shaped) accent.
500 The ASCII/Latin-1/Unicode character with that number. A
501 leading "0x" means that I<number> is hex, as in
502 C<EE<lt>0x201EE<gt>>. A leading "0" means that I<number> is octal,
503 as in C<EE<lt>075E<gt>>. Otherwise I<number> is interpreted as being
504 in decimal, as in C<EE<lt>181E<gt>>.
506 Note that older Pod formatters might not recognize octal or
507 hex numeric escapes, and that many formatters cannot reliably
508 render characters above 255. (Some formatters may even have
509 to use compromised renderings of Latin-1/CP-1252 characters, like
510 rendering C<EE<lt>eacuteE<gt>> as just a plain "e".)
514 =item C<FE<lt>filenameE<gt>> -- used for filenames
515 X<F> X<< FZ<><> >> X<POD, formatting code, filename> X<filename>
517 Typically displayed in italics. Example: "C<FE<lt>.cshrcE<gt>>"
519 =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces
520 X<S> X<< SZ<><> >> X<POD, formatting code, non-breaking space>
521 X<non-breaking space>
523 This means that the words in I<text> should not be broken
524 across lines. Example: S<C<SE<lt>$x ? $y : $zE<gt>>>.
526 =item C<XE<lt>topic nameE<gt>> -- an index entry
527 X<X> X<< XZ<><> >> X<POD, formatting code, index entry> X<index entry>
529 This is ignored by most formatters, but some may use it for building
530 indexes. It always renders as empty-string.
531 Example: C<XE<lt>absolutizing relative URLsE<gt>>
533 =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code
534 X<Z> X<< ZZ<><> >> X<POD, formatting code, null> X<null>
536 This is rarely used. It's one way to get around using an
537 EE<lt>...E<gt> code sometimes. For example, instead of
538 "C<NEE<lt>ltE<gt>3>" (for "NE<lt>3") you could write
539 "C<NZE<lt>E<gt>E<lt>3>" (the "ZE<lt>E<gt>" breaks up the "N" and
540 the "E<lt>" so they can't be considered
541 the part of a (fictitious) "NE<lt>...E<gt>" code).
544 This was formerly explained as a "zero-width character". But it in
545 most parser models, it parses to nothing at all, as opposed to parsing
546 as if it were a E<zwnj> or E<zwj>, which are REAL zero-width characters.
547 So "width" and "character" are exactly the wrong words.
551 Most of the time, you will need only a single set of angle brackets to
552 delimit the beginning and end of formatting codes. However,
553 sometimes you will want to put a real right angle bracket (a
554 greater-than sign, '>') inside of a formatting code. This is particularly
555 common when using a formatting code to provide a different font-type for a
556 snippet of code. As with all things in Perl, there is more than
557 one way to do it. One way is to simply escape the closing bracket
562 This will produce: "C<$a E<lt>=E<gt> $b>"
564 A more readable, and perhaps more "plain" way is to use an alternate
565 set of delimiters that doesn't require a single ">" to be escaped.
566 Doubled angle brackets ("<<" and ">>") may be used I<if and only if there is
567 whitespace right after the opening delimiter and whitespace right
568 before the closing delimiter!> For example, the following will
570 X<POD, formatting code, escaping with multiple brackets>
574 In fact, you can use as many repeated angle-brackets as you like so
575 long as you have the same number of them in the opening and closing
576 delimiters, and make sure that whitespace immediately follows the last
577 '<' of the opening delimiter, and immediately precedes the first '>'
578 of the closing delimiter. (The whitespace is ignored.) So the
579 following will also work:
580 X<POD, formatting code, escaping with multiple brackets>
585 And they all mean exactly the same as this:
589 The multiple-bracket form does not affect the interpretation of the contents of
590 the formatting code, only how it must end. That means that the examples above
591 are also exactly the same as this:
593 C<< $a E<lt>=E<gt> $b >>
595 As a further example, this means that if you wanted to put these bits of
596 code in C<C> (code) style:
598 open(X, ">>thing.dat") || die $!
601 you could do it like so:
603 C<<< open(X, ">>thing.dat") || die $! >>>
606 which is presumably easier to read than the old way:
608 C<open(X, "E<gt>E<gt>thing.dat") || die $!>
611 This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
612 and any other pod2xxx or Pod::Xxxx translators that use
613 Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
618 The intent is simplicity of use, not power of expression. Paragraphs
619 look like paragraphs (block format), so that they stand out
620 visually, and so that I could run them through C<fmt> easily to reformat
621 them (that's F7 in my version of B<vi>, or Esc Q in my version of
622 B<emacs>). I wanted the translator to always leave the C<'> and C<`> and
623 C<"> quotes alone, in verbatim mode, so I could slurp in a
624 working program, shift it over four spaces, and have it print out, er,
625 verbatim. And presumably in a monospace font.
627 The Pod format is not necessarily sufficient for writing a book. Pod
628 is just meant to be an idiot-proof common source for nroff, HTML,
629 TeX, and other markup languages, as used for online
630 documentation. Translators exist for B<pod2text>, B<pod2html>,
631 B<pod2man> (that's for nroff(1) and troff(1)), B<pod2latex>, and
632 B<pod2fm>. Various others are available in CPAN.
635 =head2 Embedding Pods in Perl Modules
638 You can embed Pod documentation in your Perl modules and scripts. Start
639 your documentation with an empty line, a "=head1" command at the
640 beginning, and end it with a "=cut" command and an empty line. The
641 B<perl> executable will ignore the Pod text. You can place a Pod
642 statement where B<perl> expects the beginning of a new statement, but
643 not within a statement, as that would result in an error. See any of
644 the supplied library modules for examples.
646 If you're going to put your Pod at the end of the file, and you're using
647 an C<__END__> or C<__DATA__> cut mark, make sure to put an empty line there
648 before the first Pod command.
654 Time::Local - efficiently compute time from local and GMT time
656 Without that empty line before the "=head1", many translators wouldn't
657 have recognized the "=head1" as starting a Pod block.
659 =head2 Hints for Writing Pod
664 X<podchecker> X<POD, validating>
666 The B<podchecker> command is provided for checking Pod syntax for errors
667 and warnings. For example, it checks for completely blank lines in
668 Pod blocks and for unknown commands and formatting codes. You should
669 still also pass your document through one or more translators and proofread
670 the result, or print out the result and proofread that. Some of the
671 problems found may be bugs in the translators, which you may or may not
676 If you're more familiar with writing in HTML than with writing in Pod, you
677 can try your hand at writing documentation in simple HTML, and converting
678 it to Pod with the experimental L<Pod::HTML2Pod|Pod::HTML2Pod> module,
679 (available in CPAN), and looking at the resulting code. The experimental
680 L<Pod::PXML|Pod::PXML> module in CPAN might also be useful.
684 Many older Pod translators require the lines before every Pod
685 command and after every Pod command (including "=cut"!) to be a blank
686 line. Having something like this:
688 # - - - - - - - - - - - -
689 =item $firecracker->boom()
691 This noisily detonates the firecracker object.
696 ...will make such Pod translators completely fail to see the Pod block
699 Instead, have it like this:
701 # - - - - - - - - - - - -
703 =item $firecracker->boom()
705 This noisily detonates the firecracker object.
714 Some older Pod translators require paragraphs (including command
715 paragraphs like "=head2 Functions") to be separated by I<completely>
716 empty lines. If you have an apparently empty line with some spaces
717 on it, this might not count as a separator for those translators, and
718 that could cause odd formatting.
722 Older translators might add wording around an LE<lt>E<gt> link, so that
723 C<LE<lt>Foo::BarE<gt>> may become "the Foo::Bar manpage", for example.
724 So you shouldn't write things like C<the LE<lt>fooE<gt>
725 documentation>, if you want the translated document to read sensibly.
726 Instead, write C<the LE<lt>Foo::Bar|Foo::BarE<gt> documentation> or
727 C<LE<lt>the Foo::Bar documentation|Foo::BarE<gt>>, to control how the
732 Going past the 70th column in a verbatim block might be ungracefully
733 wrapped by some formatters.
739 L<perlpodspec>, L<perlsyn/"PODs: Embedded Documentation">,
740 L<perlnewmod>, L<perldoc>, L<pod2html>, L<pod2man>, L<podchecker>.
744 Larry Wall, Sean M. Burke