1PERLPOD(1) Perl Programmers Reference Guide PERLPOD(1)
2
6 perlpod - the Plain Old Documentation format
7
9 Pod is a simple-to-use markup language used for writing documentation
10 for Perl, Perl programs, and Perl modules.
11 Translators are available for converting Pod to various formats like
13 plain text, HTML, man pages, and more.
14 Pod markup consists of three basic kinds of paragraphs: ordinary,
16 verbatim, and command.
17 Ordinary Paragraph
19 Most paragraphs in your documentation will be ordinary blocks of text,
20 like this one. You can simply type in your text without any markup
21 whatsoever, and with just a blank line before and after. When it gets
22 formatted, it will undergo minimal formatting, like being rewrapped,
23 probably put into a proportionally spaced font, and maybe even
24 justified.
25 You can use formatting codes in ordinary paragraphs, for bold, italic,
27 "code-style", hyperlinks, and more. Such codes are explained in the
28 "Formatting Codes" section, below.
29 Verbatim Paragraph
31 Verbatim paragraphs are usually used for presenting a codeblock or
32 other text which does not require any special parsing or formatting,
33 and which shouldn't be wrapped.
34 A verbatim paragraph is distinguished by having its first character be
36 a space or a tab. (And commonly, all its lines begin with spaces
37 and/or tabs.) It should be reproduced exactly, with tabs assumed to be
38 on 8-column boundaries. There are no special formatting codes, so you
39 can't italicize or anything like that. A \ means \, and nothing else.
40 Command Paragraph
42 A command paragraph is used for special treatment of whole chunks of
43 text, usually as headings or parts of lists.
44 All command paragraphs (which are typically only one line long) start
46 with "=", followed by an identifier, followed by arbitrary text that
47 the command can use however it pleases. Currently recognized commands
48 are
49 =pod
51 =head1 Heading Text
52 =head2 Heading Text
53 =head3 Heading Text
54 =head4 Heading Text
55 =over indentlevel
56 =item stuff
57 =back
58 =begin format
59 =end format
60 =for format text...
61 =encoding type
62 =cut
63 To explain them each in detail:
65 "=head1 Heading Text"
67 "=head2 Heading Text"
68 "=head3 Heading Text"
69 "=head4 Heading Text"
70 Head1 through head4 produce headings, head1 being the highest
71 level. The text in the rest of this paragraph is the content of
72 the heading. For example:
73 =head2 Object Attributes
75 The text "Object Attributes" comprises the heading there. The text
77 in these heading commands can use formatting codes, as seen here:
78 =head2 Possible Values for C<$/>
80 Such commands are explained in the "Formatting Codes" section,
82 below.
83 "=over indentlevel"
85 "=item stuff..."
86 "=back"
87 Item, over, and back require a little more explanation: "=over"
88 starts a region specifically for the generation of a list using
89 "=item" commands, or for indenting (groups of) normal paragraphs.
90 At the end of your list, use "=back" to end it. The indentlevel
91 option to "=over" indicates how far over to indent, generally in
92 ems (where one em is the width of an "M" in the document's base
93 font) or roughly comparable units; if there is no indentlevel
94 option, it defaults to four. (And some formatters may just ignore
95 whatever indentlevel you provide.) In the stuff in "=item
96 stuff...", you may use formatting codes, as seen here:
97 =item Using C<$|> to Control Buffering
99 Such commands are explained in the "Formatting Codes" section,
101 below.
102 Note also that there are some basic rules to using "=over" ...
104 "=back" regions:
105 · Don't use "=item"s outside of an "=over" ... "=back" region.
107 · The first thing after the "=over" command should be an "=item",
109 unless there aren't going to be any items at all in this
110 "=over" ... "=back" region.
111 · Don't put "=headn" commands inside an "=over" ... "=back"
113 region.
114 · And perhaps most importantly, keep the items consistent: either
116 use "=item *" for all of them, to produce bullets; or use
117 "=item 1.", "=item 2.", etc., to produce numbered lists; or use
118 "=item foo", "=item bar", etc.--namely, things that look
119 nothing like bullets or numbers.
120 If you start with bullets or numbers, stick with them, as
122 formatters use the first "=item" type to decide how to format
123 the list.
124 "=cut"
126 To end a Pod block, use a blank line, then a line beginning with
127 "=cut", and a blank line after it. This lets Perl (and the Pod
128 formatter) know that this is where Perl code is resuming. (The
129 blank line before the "=cut" is not technically necessary, but many
130 older Pod processors require it.)
131 "=pod"
133 The "=pod" command by itself doesn't do much of anything, but it
134 signals to Perl (and Pod formatters) that a Pod block starts here.
135 A Pod block starts with any command paragraph, so a "=pod" command
136 is usually used just when you want to start a Pod block with an
137 ordinary paragraph or a verbatim paragraph. For example:
138 =item stuff()
140 This function does stuff.
142 =cut
144 sub stuff {
146 ...
147 }
148 =pod
150 Remember to check its return value, as in:
152 stuff() || die "Couldn't do stuff!";
154 =cut
156 "=begin formatname"
158 "=end formatname"
159 "=for formatname text..."
160 For, begin, and end will let you have regions of text/code/data
161 that are not generally interpreted as normal Pod text, but are
162 passed directly to particular formatters, or are otherwise special.
163 A formatter that can use that format will use the region, otherwise
164 it will be completely ignored.
165 A command "=begin formatname", some paragraphs, and a command "=end
167 formatname", mean that the text/data in between is meant for
168 formatters that understand the special format called formatname.
169 For example,
170 =begin html
172 <hr> <img src="thang.png">
174 <p> This is a raw HTML paragraph </p>
175 =end html
177 The command "=for formatname text..." specifies that the remainder
179 of just this paragraph (starting right after formatname) is in that
180 special format.
181 =for html <hr> <img src="thang.png">
183 <p> This is a raw HTML paragraph </p>
184 This means the same thing as the above "=begin html" ... "=end
186 html" region.
187 That is, with "=for", you can have only one paragraph's worth of
189 text (i.e., the text in "=foo targetname text..."), but with
190 "=begin targetname" ... "=end targetname", you can have any amount
191 of stuff in between. (Note that there still must be a blank line
192 after the "=begin" command and a blank line before the "=end"
193 command.)
194 Here are some examples of how to use these:
196 =begin html
198 <br>Figure 1.<br><IMG SRC="figure1.png"><br>
200 =end html
202 =begin text
204 ---------------
206 | foo |
207 | bar |
208 ---------------
209 ^^^^ Figure 1. ^^^^
211 =end text
213 Some format names that formatters currently are known to accept
215 include "roff", "man", "latex", "tex", "text", and "html". (Some
216 formatters will treat some of these as synonyms.)
217 A format name of "comment" is common for just making notes
219 (presumably to yourself) that won't appear in any formatted version
220 of the Pod document:
221 =for comment
223 Make sure that all the available options are documented!
224 Some formatnames will require a leading colon (as in "=for
226 :formatname", or "=begin :formatname" ... "=end :formatname"), to
227 signal that the text is not raw data, but instead is Pod text
228 (i.e., possibly containing formatting codes) that's just not for
229 normal formatting (e.g., may not be a normal-use paragraph, but
230 might be for formatting as a footnote).
231 "=encoding encodingname"
233 This command is used for declaring the encoding of a document.
234 Most users won't need this; but if your encoding isn't US-ASCII,
235 then put a "=encoding encodingname" command very early in the
236 document so that pod formatters will know how to decode the
237 document. For encodingname, use a name recognized by the
238 Encode::Supported module. Some pod formatters may try to guess
239 between a Latin-1 or CP-1252 versus UTF-8 encoding, but they may
240 guess wrong. It's best to be explicit if you use anything besides
241 strict ASCII. Examples:
242 =encoding latin1
244 =encoding utf8
246 =encoding koi8-r
248 =encoding ShiftJIS
250 =encoding big5
252 "=encoding" affects the whole document, and must occur only once.
254 And don't forget, all commands but "=encoding" last up until the end of
256 its paragraph, not its line. So in the examples below, you can see
257 that every command needs the blank line after it, to end its paragraph.
258 (And some older Pod translators may require the "=encoding" line to
259 have a following blank line as well, even though it should be legal to
260 omit.)
261 Some examples of lists include:
263 =over
265 =item *
267 First item
269 =item *
271 Second item
273 =back
275 =over
277 =item Foo()
279 Description of Foo function
281 =item Bar()
283 Description of Bar function
285 =back
287 Formatting Codes
289 In ordinary paragraphs and in some command paragraphs, various
290 formatting codes (a.k.a. "interior sequences") can be used:
291 "I<text>" -- italic text
293 Used for emphasis (""be I<careful!>"") and parameters (""redo
294 I<LABEL>"")
295 "B<text>" -- bold text
297 Used for switches (""perl's B<-n> switch""), programs (""some
298 systems provide a B<chfn> for that""), emphasis (""be
299 B<careful!>""), and so on (""and that feature is known as
300 B<autovivification>"").
301 "C<code>" -- code text
303 Renders code in a typewriter font, or gives some other indication
304 that this represents program text (""C<gmtime($^T)>"") or some
305 other form of computerese (""C<drwxr-xr-x>"").
306 "L<name>" -- a hyperlink
308 There are various syntaxes, listed below. In the syntaxes given,
309 "text", "name", and "section" cannot contain the characters '/' and
310 '|'; and any '<' or '>' should be matched.
311 · "L<name>"
313 Link to a Perl manual page (e.g., "L<Net::Ping>"). Note that
315 "name" should not contain spaces. This syntax is also
316 occasionally used for references to Unix man pages, as in
317 "L<crontab(5)>".
318 · "L<name/"sec">" or "L<name/sec>"
320 Link to a section in other manual page. E.g., "L<perlsyn/"For
322 Loops">"
323 · "L</"sec">" or "L</sec>"
325 Link to a section in this manual page. E.g., "L</"Object
327 Methods">"
328 A section is started by the named heading or item. For example,
330 "L<perlvar/$.>" or "L<perlvar/"$.">" both link to the section
331 started by ""=item $."" in perlvar. And "L<perlsyn/For Loops>" or
332 "L<perlsyn/"For Loops">" both link to the section started by
333 ""=head2 For Loops"" in perlsyn.
334 To control what text is used for display, you use ""L<text|...>"",
336 as in:
337 · "L<text|name>"
339 Link this text to that manual page. E.g., "L<Perl Error
341 Messages|perldiag>"
342 · "L<text|name/"sec">" or "L<text|name/sec>"
344 Link this text to that section in that manual page. E.g.,
346 "L<postfix "if"|perlsyn/"Statement Modifiers">"
347 · "L<text|/"sec">" or "L<text|/sec>" or "L<text|"sec">"
349 Link this text to that section in this manual page. E.g.,
351 "L<the various attributes|/"Member Data">"
352 Or you can link to a web page:
354 · "L<scheme:...>"
356 "L<text|scheme:...>"
358 Links to an absolute URL. For example,
360 "L<http://www.perl.org/>" or "L<The Perl Home
361 Page|http://www.perl.org/>".
362 "E<escape>" -- a character escape
364 Very similar to HTML/XML "&foo;" "entity references":
365 · "E<lt>" -- a literal < (less than)
367 · "E<gt>" -- a literal > (greater than)
369 · "E<verbar>" -- a literal | (vertical bar)
371 · "E<sol>" -- a literal / (solidus)
373 The above four are optional except in other formatting codes,
375 notably "L<...>", and when preceded by a capital letter.
376 · "E<htmlname>"
378 Some non-numeric HTML entity name, such as "E<eacute>", meaning
380 the same thing as "é" in HTML -- i.e., a lowercase e
381 with an acute (/-shaped) accent.
382 · "E<number>"
384 The ASCII/Latin-1/Unicode character with that number. A
386 leading "0x" means that number is hex, as in "E<0x201E>". A
387 leading "0" means that number is octal, as in "E<075>".
388 Otherwise number is interpreted as being in decimal, as in
389 "E<181>".
390 Note that older Pod formatters might not recognize octal or hex
392 numeric escapes, and that many formatters cannot reliably
393 render characters above 255. (Some formatters may even have to
394 use compromised renderings of Latin-1/CP-1252 characters, like
395 rendering "E<eacute>" as just a plain "e".)
396 "F<filename>" -- used for filenames
398 Typically displayed in italics. Example: ""F<.cshrc>""
399 "S<text>" -- text contains non-breaking spaces
401 This means that the words in text should not be broken across
402 lines. Example: "S<$x ? $y : $z>".
403 "X<topic name>" -- an index entry
405 This is ignored by most formatters, but some may use it for
406 building indexes. It always renders as empty-string. Example:
407 "X<absolutizing relative URLs>"
408 "Z<>" -- a null (zero-effect) formatting code
410 This is rarely used. It's one way to get around using an E<...>
411 code sometimes. For example, instead of ""NE<lt>3"" (for "N<3")
412 you could write ""NZ<><3"" (the "Z<>" breaks up the "N" and the "<"
413 so they can't be considered the part of a (fictitious) "N<...>"
414 code).
415 Most of the time, you will need only a single set of angle brackets to
417 delimit the beginning and end of formatting codes. However, sometimes
418 you will want to put a real right angle bracket (a greater-than sign,
419 '>') inside of a formatting code. This is particularly common when
420 using a formatting code to provide a different font-type for a snippet
421 of code. As with all things in Perl, there is more than one way to do
422 it. One way is to simply escape the closing bracket using an "E" code:
423 C<$a E<lt>=E<gt> $b>
425 This will produce: ""$a <=> $b""
427 A more readable, and perhaps more "plain" way is to use an alternate
429 set of delimiters that doesn't require a single ">" to be escaped.
430 Doubled angle brackets ("<<" and ">>") may be used if and only if there
431 is whitespace right after the opening delimiter and whitespace right
432 before the closing delimiter! For example, the following will do the
433 trick:
434 C<< $a <=> $b >>
436 In fact, you can use as many repeated angle-brackets as you like so
438 long as you have the same number of them in the opening and closing
439 delimiters, and make sure that whitespace immediately follows the last
440 '<' of the opening delimiter, and immediately precedes the first '>' of
441 the closing delimiter. (The whitespace is ignored.) So the following
442 will also work:
443 C<<< $a <=> $b >>>
445 C<<<< $a <=> $b >>>>
446 And they all mean exactly the same as this:
448 C<$a E<lt>=E<gt> $b>
450 The multiple-bracket form does not affect the interpretation of the
452 contents of the formatting code, only how it must end. That means that
453 the examples above are also exactly the same as this:
454 C<< $a E<lt>=E<gt> $b >>
456 As a further example, this means that if you wanted to put these bits
458 of code in "C" (code) style:
459 open(X, ">>thing.dat") || die $!
461 $foo->bar();
462 you could do it like so:
464 C<<< open(X, ">>thing.dat") || die $! >>>
466 C<< $foo->bar(); >>
467 which is presumably easier to read than the old way:
469 C<open(X, "E<gt>E<gt>thing.dat") || die $!>
471 C<$foo-E<gt>bar();>
472 This is currently supported by pod2text (Pod::Text), pod2man
474 (Pod::Man), and any other pod2xxx or Pod::Xxxx translators that use
475 Pod::Parser 1.093 or later, or Pod::Tree 1.02 or later.
476 The Intent
478 The intent is simplicity of use, not power of expression. Paragraphs
479 look like paragraphs (block format), so that they stand out visually,
480 and so that I could run them through "fmt" easily to reformat them
481 (that's F7 in my version of vi, or Esc Q in my version of emacs). I
482 wanted the translator to always leave the "'" and "`" and """ quotes
483 alone, in verbatim mode, so I could slurp in a working program, shift
484 it over four spaces, and have it print out, er, verbatim. And
485 presumably in a monospace font.
486 The Pod format is not necessarily sufficient for writing a book. Pod
488 is just meant to be an idiot-proof common source for nroff, HTML, TeX,
489 and other markup languages, as used for online documentation.
490 Translators exist for pod2text, pod2html, pod2man (that's for nroff(1)
491 and troff(1)), pod2latex, and pod2fm. Various others are available in
492 CPAN.
493 Embedding Pods in Perl Modules
495 You can embed Pod documentation in your Perl modules and scripts.
496 Start your documentation with an empty line, a "=head1" command at the
497 beginning, and end it with a "=cut" command and an empty line. The
498 perl executable will ignore the Pod text. You can place a Pod
499 statement where perl expects the beginning of a new statement, but not
500 within a statement, as that would result in an error. See any of the
501 supplied library modules for examples.
502 If you're going to put your Pod at the end of the file, and you're
504 using an "__END__" or "__DATA__" cut mark, make sure to put an empty
505 line there before the first Pod command.
506 __END__
508 =head1 NAME
510 Time::Local - efficiently compute time from local and GMT time
512 Without that empty line before the "=head1", many translators wouldn't
514 have recognized the "=head1" as starting a Pod block.
515 Hints for Writing Pod
517 ·
518 The podchecker command is provided for checking Pod syntax for
521 errors and warnings. For example, it checks for completely blank
522 lines in Pod blocks and for unknown commands and formatting codes.
523 You should still also pass your document through one or more
524 translators and proofread the result, or print out the result and
525 proofread that. Some of the problems found may be bugs in the
526 translators, which you may or may not wish to work around.
527 · If you're more familiar with writing in HTML than with writing in
529 Pod, you can try your hand at writing documentation in simple HTML,
530 and converting it to Pod with the experimental Pod::HTML2Pod
531 module, (available in CPAN), and looking at the resulting code.
532 The experimental Pod::PXML module in CPAN might also be useful.
533 · Many older Pod translators require the lines before every Pod
535 command and after every Pod command (including "=cut"!) to be a
536 blank line. Having something like this:
537 # - - - - - - - - - - - -
539 =item $firecracker->boom()
540 This noisily detonates the firecracker object.
542 =cut
543 sub boom {
544 ...
545 ...will make such Pod translators completely fail to see the Pod
547 block at all.
548 Instead, have it like this:
550 # - - - - - - - - - - - -
552 =item $firecracker->boom()
554 This noisily detonates the firecracker object.
556 =cut
558 sub boom {
560 ...
561 · Some older Pod translators require paragraphs (including command
563 paragraphs like "=head2 Functions") to be separated by completely
564 empty lines. If you have an apparently empty line with some spaces
565 on it, this might not count as a separator for those translators,
566 and that could cause odd formatting.
567 · Older translators might add wording around an L<> link, so that
569 "L<Foo::Bar>" may become "the Foo::Bar manpage", for example. So
570 you shouldn't write things like "the L<foo> documentation", if you
571 want the translated document to read sensibly. Instead, write "the
572 L<Foo::Bar|Foo::Bar> documentation" or "L<the Foo::Bar
573 documentation|Foo::Bar>", to control how the link comes out.
574 · Going past the 70th column in a verbatim block might be
576 ungracefully wrapped by some formatters.
577
579 perlpodspec, "PODs: Embedded Documentation" in perlsyn, perlnewmod,
580 perldoc, pod2html, pod2man, podchecker.
581
583 Larry Wall, Sean M. Burke
584perl v5.28.2 2018-03-01 PERLPOD(1)