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>
299 C<=encoding> affects the whole document, and must occur only once.
303 And don't forget, all commands but C<=encoding> last 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. (And some older
307 Pod translators may require the C<=encoding> line to be similarly
310 Some examples of lists include:
328 Description of Foo function
332 Description of Bar function
337 =head2 Formatting Codes
338 X<POD, formatting code> X<formatting code>
339 X<POD, interior sequence> X<interior sequence>
341 In ordinary paragraphs and in some command paragraphs, various
342 formatting codes (a.k.a. "interior sequences") can be used:
345 "interior sequences" is such an opaque term.
346 Prefer "formatting codes" instead.
350 =item C<IE<lt>textE<gt>> -- italic text
351 X<I> X<< IZ<><> >> X<POD, formatting code, italic> X<italic>
353 Used for emphasis ("C<be IE<lt>careful!E<gt>>") and parameters
354 ("C<redo IE<lt>LABELE<gt>>")
356 =item C<BE<lt>textE<gt>> -- bold text
357 X<B> X<< BZ<><> >> X<POD, formatting code, bold> X<bold>
359 Used for switches ("C<perl's BE<lt>-nE<gt> switch>"), programs
360 ("C<some systems provide a BE<lt>chfnE<gt> for that>"),
361 emphasis ("C<be BE<lt>careful!E<gt>>"), and so on
362 ("C<and that feature is known as BE<lt>autovivificationE<gt>>").
364 =item C<CE<lt>codeE<gt>> -- code text
365 X<C> X<< CZ<><> >> X<POD, formatting code, code> X<code>
367 Renders code in a typewriter font, or gives some other indication that
368 this represents program text ("C<CE<lt>gmtime($^T)E<gt>>") or some other
369 form of computerese ("C<CE<lt>drwxr-xr-xE<gt>>").
371 =item C<LE<lt>nameE<gt>> -- a hyperlink
372 X<L> X<< LZ<><> >> X<POD, formatting code, hyperlink> X<hyperlink>
374 There are various syntaxes, listed below. In the syntaxes given,
375 C<text>, C<name>, and C<section> cannot contain the characters
376 '/' and '|'; and any '<' or '>' should be matched.
384 Link to a Perl manual page (e.g., C<LE<lt>Net::PingE<gt>>). Note
385 that C<name> should not contain spaces. This syntax
386 is also occasionally used for references to Unix man pages, as in
387 C<LE<lt>crontab(5)E<gt>>.
391 C<LE<lt>name/"sec"E<gt>> or C<LE<lt>name/secE<gt>>
393 Link to a section in other manual page. E.g.,
394 C<LE<lt>perlsyn/"For Loops"E<gt>>
398 C<LE<lt>/"sec"E<gt>> or C<LE<lt>/secE<gt>>
400 Link to a section in this manual page. E.g.,
401 C<LE<lt>/"Object Methods"E<gt>>
405 A section is started by the named heading or item. For
406 example, C<LE<lt>perlvar/$.E<gt>> or C<LE<lt>perlvar/"$."E<gt>> both
407 link to the section started by "C<=item $.>" in perlvar. And
408 C<LE<lt>perlsyn/For LoopsE<gt>> or C<LE<lt>perlsyn/"For Loops"E<gt>>
409 both link to the section started by "C<=head2 For Loops>"
412 To control what text is used for display, you
413 use "C<LE<lt>text|...E<gt>>", as in:
419 C<LE<lt>text|nameE<gt>>
421 Link this text to that manual page. E.g.,
422 C<LE<lt>Perl Error Messages|perldiagE<gt>>
426 C<LE<lt>text|name/"sec"E<gt>> or C<LE<lt>text|name/secE<gt>>
428 Link this text to that section in that manual page. E.g.,
429 C<LE<lt>postfix "if"|perlsyn/"Statement Modifiers"E<gt>>
433 C<LE<lt>text|/"sec"E<gt>> or C<LE<lt>text|/secE<gt>>
434 or C<LE<lt>text|"sec"E<gt>>
436 Link this text to that section in this manual page. E.g.,
437 C<LE<lt>the various attributes|/"Member Data"E<gt>>
441 Or you can link to a web page:
447 C<LE<lt>scheme:...E<gt>>
449 C<LE<lt>text|scheme:...E<gt>>
451 Links to an absolute URL. For example, C<LE<lt>http://www.perl.org/E<gt>> or
452 C<LE<lt>The Perl Home Page|http://www.perl.org/E<gt>>.
456 =item C<EE<lt>escapeE<gt>> -- a character escape
457 X<E> X<< EZ<><> >> X<POD, formatting code, escape> X<escape>
459 Very similar to HTML/XML C<&I<foo>;> "entity references":
465 C<EE<lt>ltE<gt>> -- a literal E<lt> (less than)
469 C<EE<lt>gtE<gt>> -- a literal E<gt> (greater than)
473 C<EE<lt>verbarE<gt>> -- a literal | (I<ver>tical I<bar>)
477 C<EE<lt>solE<gt>> -- a literal / (I<sol>idus)
479 The above four are optional except in other formatting codes,
480 notably C<LE<lt>...E<gt>>, and when preceded by a
485 C<EE<lt>htmlnameE<gt>>
487 Some non-numeric HTML entity name, such as C<EE<lt>eacuteE<gt>>,
488 meaning the same thing as C<é> in HTML -- i.e., a lowercase
489 e with an acute (/-shaped) accent.
495 The ASCII/Latin-1/Unicode character with that number. A
496 leading "0x" means that I<number> is hex, as in
497 C<EE<lt>0x201EE<gt>>. A leading "0" means that I<number> is octal,
498 as in C<EE<lt>075E<gt>>. Otherwise I<number> is interpreted as being
499 in decimal, as in C<EE<lt>181E<gt>>.
501 Note that older Pod formatters might not recognize octal or
502 hex numeric escapes, and that many formatters cannot reliably
503 render characters above 255. (Some formatters may even have
504 to use compromised renderings of Latin-1 characters, like
505 rendering C<EE<lt>eacuteE<gt>> as just a plain "e".)
509 =item C<FE<lt>filenameE<gt>> -- used for filenames
510 X<F> X<< FZ<><> >> X<POD, formatting code, filename> X<filename>
512 Typically displayed in italics. Example: "C<FE<lt>.cshrcE<gt>>"
514 =item C<SE<lt>textE<gt>> -- text contains non-breaking spaces
515 X<S> X<< SZ<><> >> X<POD, formatting code, non-breaking space>
516 X<non-breaking space>
518 This means that the words in I<text> should not be broken
519 across lines. Example: S<C<SE<lt>$x ? $y : $zE<gt>>>.
521 =item C<XE<lt>topic nameE<gt>> -- an index entry
522 X<X> X<< XZ<><> >> X<POD, formatting code, index entry> X<index entry>
524 This is ignored by most formatters, but some may use it for building
525 indexes. It always renders as empty-string.
526 Example: C<XE<lt>absolutizing relative URLsE<gt>>
528 =item C<ZE<lt>E<gt>> -- a null (zero-effect) formatting code
529 X<Z> X<< ZZ<><> >> X<POD, formatting code, null> X<null>
531 This is rarely used. It's one way to get around using an
532 EE<lt>...E<gt> code sometimes. For example, instead of
533 "C<NEE<lt>ltE<gt>3>" (for "NE<lt>3") you could write
534 "C<NZE<lt>E<gt>E<lt>3>" (the "ZE<lt>E<gt>" breaks up the "N" and
535 the "E<lt>" so they can't be considered
536 the part of a (fictitious) "NE<lt>...E<gt>" code).
539 This was formerly explained as a "zero-width character". But it in
540 most parser models, it parses to nothing at all, as opposed to parsing
541 as if it were a E<zwnj> or E<zwj>, which are REAL zero-width characters.
542 So "width" and "character" are exactly the wrong words.
546 Most of the time, you will need only a single set of angle brackets to
547 delimit the beginning and end of formatting codes. However,
548 sometimes you will want to put a real right angle bracket (a
549 greater-than sign, '>') inside of a formatting code. This is particularly
550 common when using a formatting code to provide a different font-type for a
551 snippet of code. As with all things in Perl, there is more than
552 one way to do it. One way is to simply escape the closing bracket
557 This will produce: "C<$a E<lt>=E<gt> $b>"
559 A more readable, and perhaps more "plain" way is to use an alternate
560 set of delimiters that doesn't require a single ">" to be escaped.
561 Doubled angle brackets ("<<" and ">>") may be used I<if and only if there is
562 whitespace right after the opening delimiter and whitespace right
563 before the closing delimiter!> For example, the following will
565 X<POD, formatting code, escaping with multiple brackets>
569 In fact, you can use as many repeated angle-brackets as you like so
570 long as you have the same number of them in the opening and closing
571 delimiters, and make sure that whitespace immediately follows the last
572 '<' of the opening delimiter, and immediately precedes the first '>'
573 of the closing delimiter. (The whitespace is ignored.) So the
574 following will also work:
575 X<POD, formatting code, escaping with multiple brackets>
580 And they all mean exactly the same as this:
584 The multiple-bracket form does not affect the interpretation of the contents of
585 the formatting code, only how it must end. That means that the examples above
586 are also exactly the same as this:
588 C<< $a E<lt>=E<gt> $b >>
590 As a further example, this means that if you wanted to put these bits of
591 code in C<C> (code) style:
593 open(X, ">>thing.dat") || die $!
596 you could do it like so:
598 C<<< open(X, ">>thing.dat") || die $! >>>
601 which is presumably easier to read than the old way:
603 C<open(X, "E<gt>E<gt>thing.dat") || die $!>
606 This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
607 and any other pod2xxx or Pod::Xxxx translators that use
608 Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
613 The intent is simplicity of use, not power of expression. Paragraphs
614 look like paragraphs (block format), so that they stand out
615 visually, and so that I could run them through C<fmt> easily to reformat
616 them (that's F7 in my version of B<vi>, or Esc Q in my version of
617 B<emacs>). I wanted the translator to always leave the C<'> and C<`> and
618 C<"> quotes alone, in verbatim mode, so I could slurp in a
619 working program, shift it over four spaces, and have it print out, er,
620 verbatim. And presumably in a monospace font.
622 The Pod format is not necessarily sufficient for writing a book. Pod
623 is just meant to be an idiot-proof common source for nroff, HTML,
624 TeX, and other markup languages, as used for online
625 documentation. Translators exist for B<pod2text>, B<pod2html>,
626 B<pod2man> (that's for nroff(1) and troff(1)), B<pod2latex>, and
627 B<pod2fm>. Various others are available in CPAN.
630 =head2 Embedding Pods in Perl Modules
633 You can embed Pod documentation in your Perl modules and scripts. Start
634 your documentation with an empty line, a "=head1" command at the
635 beginning, and end it with a "=cut" command and an empty line. The
636 B<perl> executable will ignore the Pod text. You can place a Pod
637 statement where B<perl> expects the beginning of a new statement, but
638 not within a statement, as that would result in an error. See any of
639 the supplied library modules for examples.
641 If you're going to put your Pod at the end of the file, and you're using
642 an C<__END__> or C<__DATA__> cut mark, make sure to put an empty line there
643 before the first Pod command.
649 Time::Local - efficiently compute time from local and GMT time
651 Without that empty line before the "=head1", many translators wouldn't
652 have recognized the "=head1" as starting a Pod block.
654 =head2 Hints for Writing Pod
659 X<podchecker> X<POD, validating>
661 The B<podchecker> command is provided for checking Pod syntax for errors
662 and warnings. For example, it checks for completely blank lines in
663 Pod blocks and for unknown commands and formatting codes. You should
664 still also pass your document through one or more translators and proofread
665 the result, or print out the result and proofread that. Some of the
666 problems found may be bugs in the translators, which you may or may not
671 If you're more familiar with writing in HTML than with writing in Pod, you
672 can try your hand at writing documentation in simple HTML, and converting
673 it to Pod with the experimental L<Pod::HTML2Pod|Pod::HTML2Pod> module,
674 (available in CPAN), and looking at the resulting code. The experimental
675 L<Pod::PXML|Pod::PXML> module in CPAN might also be useful.
679 Many older Pod translators require the lines before every Pod
680 command and after every Pod command (including "=cut"!) to be a blank
681 line. Having something like this:
683 # - - - - - - - - - - - -
684 =item $firecracker->boom()
686 This noisily detonates the firecracker object.
691 ...will make such Pod translators completely fail to see the Pod block
694 Instead, have it like this:
696 # - - - - - - - - - - - -
698 =item $firecracker->boom()
700 This noisily detonates the firecracker object.
709 Some older Pod translators require paragraphs (including command
710 paragraphs like "=head2 Functions") to be separated by I<completely>
711 empty lines. If you have an apparently empty line with some spaces
712 on it, this might not count as a separator for those translators, and
713 that could cause odd formatting.
717 Older translators might add wording around an LE<lt>E<gt> link, so that
718 C<LE<lt>Foo::BarE<gt>> may become "the Foo::Bar manpage", for example.
719 So you shouldn't write things like C<the LE<lt>fooE<gt>
720 documentation>, if you want the translated document to read sensibly.
721 Instead, write C<the LE<lt>Foo::Bar|Foo::BarE<gt> documentation> or
722 C<LE<lt>the Foo::Bar documentation|Foo::BarE<gt>>, to control how the
727 Going past the 70th column in a verbatim block might be ungracefully
728 wrapped by some formatters.
734 L<perlpodspec>, L<perlsyn/"PODs: Embedded Documentation">,
735 L<perlnewmod>, L<perldoc>, L<pod2html>, L<pod2man>, L<podchecker>.
739 Larry Wall, Sean M. Burke