PERLPOD(1) Perl Programmers Reference Guide PERLPOD(1)
NAME
perlpod - the Plain Old Documentation format
DESCRIPTION
Pod is a simple-to-use markup language used for writing documentation for Perl, Perl programs, and Perl
modules.
Translators are available for converting Pod to various formats like plain text, HTML, man pages, and more.
Pod markup consists of three basic kinds of paragraphs: ordinary, verbatim, and command.
Ordinary Paragraph
Most paragraphs in your documentation will be ordinary blocks of text, like this one. You can simply type in
your text without any markup whatsoever, and with just a blank line before and after. When it gets formatted,
it will undergo minimal formatting, like being rewrapped, probably put into a proportionally spaced font, and
maybe even justified.
You can use formatting codes in ordinary paragraphs, for bold, italic, "code-style", hyperlinks, and more.
Such codes are explained in the "Formatting Codes" section, below.
Verbatim Paragraph
Verbatim paragraphs are usually used for presenting a codeblock or other text which does not require any
special parsing or formatting, and which shouldn't be wrapped.
A verbatim paragraph is distinguished by having its first character be a space or a tab. (And commonly, all
its lines begin with spaces and/or tabs.) It should be reproduced exactly, with tabs assumed to be on
8-column boundaries. There are no special formatting codes, so you can't italicize or anything like that. A
\ means \, and nothing else.
Command Paragraph
A command paragraph is used for special treatment of whole chunks of text, usually as headings or parts of
lists.
All command paragraphs (which are typically only one line long) start with "=", followed by an identifier,
followed by arbitrary text that the command can use however it pleases. Currently recognized commands are
=pod
=head1 Heading Text
=head2 Heading Text
=head3 Heading Text
=head4 Heading Text
=over indentlevel
=item stuff
=back
=begin format
=end format
=for format text...
=encoding type
=cut
To explain them each in detail:
"=head1 Heading Text"
"=head2 Heading Text"
"=head3 Heading Text"
"=head4 Heading Text"
"=over indentlevel"
"=item stuff..."
"=back"
Item, over, and back require a little more explanation: "=over" starts a region specifically for the
generation of a list using "=item" commands, or for indenting (groups of) normal paragraphs. At the end
of your list, use "=back" to end it. The indentlevel option to "=over" indicates how far over to indent,
generally in ems (where one em is the width of an "M" in the document's base font) or roughly comparable
units; if there is no indentlevel option, it defaults to four. (And some formatters may just ignore
whatever indentlevel you provide.) In the stuff in "=item stuff...", you may use formatting codes, as
seen here:
=item Using C<$|> to Control Buffering
Such commands are explained in the "Formatting Codes" section, below.
Note also that there are some basic rules to using "=over" ... "=back" regions:
· Don't use "=item"s outside of an "=over" ... "=back" region.
· The first thing after the "=over" command should be an "=item", unless there aren't going to be any
items at all in this "=over" ... "=back" region.
· Don't put "=headn" commands inside an "=over" ... "=back" region.
· And perhaps most importantly, keep the items consistent: either use "=item *" for all of them, to
produce bullets; or use "=item 1.", "=item 2.", etc., to produce numbered lists; or use "=item foo",
"=item bar", etc.--namely, things that look nothing like bullets or numbers.
If you start with bullets or numbers, stick with them, as formatters use the first "=item" type to
decide how to format the list.
"=cut"
To end a Pod block, use a blank line, then a line beginning with "=cut", and a blank line after it. This
lets Perl (and the Pod formatter) know that this is where Perl code is resuming. (The blank line before
the "=cut" is not technically necessary, but many older Pod processors require it.)
"=pod"
The "=pod" command by itself doesn't do much of anything, but it signals to Perl (and Pod formatters) that
a Pod block starts here. A Pod block starts with any command paragraph, so a "=pod" command is usually
used just when you want to start a Pod block with an ordinary paragraph or a verbatim paragraph. For
example:
=item stuff()
This function does stuff.
=cut
sub stuff {
...
}
=pod
that can use that format will use the region, otherwise it will be completely ignored.
A command "=begin formatname", some paragraphs, and a command "=end formatname", mean that the text/data
in between is meant for formatters that understand the special format called formatname. For example,
=begin html
<hr> <img src="thang.png">
<p> This is a raw HTML paragraph </p>
=end html
The command "=for formatname text..." specifies that the remainder of just this paragraph (starting right
after formatname) is in that special format.
=for html <hr> <img src="thang.png">
<p> This is a raw HTML paragraph </p>
This means the same thing as the above "=begin html" ... "=end html" region.
That is, with "=for", you can have only one paragraph's worth of text (i.e., the text in "=foo targetname
text..."), but with "=begin targetname" ... "=end targetname", you can have any amount of stuff in
between. (Note that there still must be a blank line after the "=begin" command and a blank line before
the "=end" command.
Here are some examples of how to use these:
=begin html
<br>Figure 1.<br><IMG SRC="figure1.png"><br>
=end html
=begin text
---------------
| foo |
| bar |
---------------
^^^^ Figure 1. ^^^^
=end text
Some format names that formatters currently are known to accept include "roff", "man", "latex", "tex",
"text", and "html". (Some formatters will treat some of these as synonyms.)
A format name of "comment" is common for just making notes (presumably to yourself) that won't appear in
any formatted version of the Pod document:
=for comment
Make sure that all the available options are documented!
Some formatnames will require a leading colon (as in "=for :formatname", or "=begin :formatname" ... "=end
=encoding koi8-r
=encoding ShiftJIS
=encoding big5
"=encoding" affects the whole document, and must occur only once.
And don't forget, when using any other command, that the command lasts up until the end of its paragraph, not
its line. So in the examples below, you can see that every command needs the blank line after it, to end its
paragraph.
Some examples of lists include:
=over
=item *
First item
=item *
Second item
=back
=over
=item Foo()
Description of Foo function
=item Bar()
Description of Bar function
=back
Formatting Codes
In ordinary paragraphs and in some command paragraphs, various formatting codes (a.k.a. "interior sequences")
can be used:
"I<text>" -- italic text
Used for emphasis (""be I<careful!>"") and parameters (""redo I<LABEL>"")
"B<text>" -- bold text
Used for switches (""perl's B<-n> switch""), programs (""some systems provide a B<chfn> for that""),
emphasis (""be B<careful!>""), and so on (""and that feature is known as B<autovivification>"").
"C<code>" -- code text
Renders code in a typewriter font, or gives some other indication that this represents program text
(""C<gmtime($^T)>"") or some other form of computerese (""C<drwxr-xr-x>"").
"L<name>" -- a hyperlink
· "L</"sec">" or "L</sec>"
Link to a section in this manual page. E.g., "L</"Object Methods">"
A section is started by the named heading or item. For example, "L<perlvar/$.>" or "L<perlvar/"$.">" both
link to the section started by ""=item $."" in perlvar. And "L<perlsyn/For Loops>" or "L<perlsyn/"For
Loops">" both link to the section started by ""=head2 For Loops"" in perlsyn.
To control what text is used for display, you use ""L<text|...>"", as in:
· "L<text|name>"
Link this text to that manual page. E.g., "L<Perl Error Messages|perldiag>"
· "L<text|name/"sec">" or "L<text|name/sec>"
Link this text to that section in that manual page. E.g., "L<postfix "if"|perlsyn/"Statement
Modifiers">"
· "L<text|/"sec">" or "L<text|/sec>" or "L<text|"sec">"
Link this text to that section in this manual page. E.g., "L<the various attributes|/"Member Data">"
Or you can link to a web page:
· "L<scheme:...>"
"L<text|scheme:...>"
Links to an absolute URL. For example, "L<http://www.perl.org/>" or "L<The Perl Home
Page|http://www.perl.org/>".
"E<escape>" -- a character escape
Very similar to HTML/XML "&foo;" "entity references":
· "E<lt>" -- a literal < (less than)
· "E<gt>" -- a literal > (greater than)
· "E<verbar>" -- a literal | (vertical bar)
· "E<sol>" -- a literal / (solidus)
The above four are optional except in other formatting codes, notably "L<...>", and when preceded by a
capital letter.
· "E<htmlname>"
Some non-numeric HTML entity name, such as "E<eacute>", meaning the same thing as "é" in HTML
-- i.e., a lowercase e with an acute (/-shaped) accent.
· "E<number>"
The ASCII/Latin-1/Unicode character with that number. A leading "0x" means that number is hex, as in
"X<topic name>" -- an index entry
This is ignored by most formatters, but some may use it for building indexes. It always renders as empty-
string. Example: "X<absolutizing relative URLs>"
"Z<>" -- a null (zero-effect) formatting code
This is rarely used. It's one way to get around using an E<...> code sometimes. For example, instead of
""NE<lt>3"" (for "N<3") you could write ""NZ<><3"" (the "Z<>" breaks up the "N" and the "<" so they can't
be considered the part of a (fictitious) "N<...>" code.
Most of the time, you will need only a single set of angle brackets to delimit the beginning and end of
formatting codes. However, sometimes you will want to put a real right angle bracket (a greater-than sign,
'>') inside of a formatting code. This is particularly common when using a formatting code to provide a
different font-type for a snippet of code. As with all things in Perl, there is more than one way to do it.
One way is to simply escape the closing bracket using an "E" code:
C<$a E<lt>=E<gt> $b>
This will produce: ""$a <=> $b""
A more readable, and perhaps more "plain" way is to use an alternate set of delimiters that doesn't require a
single ">" to be escaped. Doubled angle brackets ("<<" and ">>") may be used if and only if there is
whitespace right after the opening delimiter and whitespace right before the closing delimiter! For example,
the following will do the trick:
C<< $a <=> $b >>
In fact, you can use as many repeated angle-brackets as you like so long as you have the same number of them
in the opening and closing delimiters, and make sure that whitespace immediately follows the last '<' of the
opening delimiter, and immediately precedes the first '>' of the closing delimiter. (The whitespace is
ignored.) So the following will also work:
C<<< $a <=> $b >>>
C<<<< $a <=> $b >>>>
And they all mean exactly the same as this:
C<$a E<lt>=E<gt> $b>
The multiple-bracket form does not affect the interpretation of the contents of the formatting code, only how
it must end. That means that the examples above are also exactly the same as this:
C<< $a E<lt>=E<gt> $b >>
As a further example, this means that if you wanted to put these bits of code in "C" (code) style:
open(X, ">>thing.dat") || die $!
$foo->bar();
you could do it like so:
C<<< open(X, ">>thing.dat") || die $! >>>
C<< $foo->bar(); >>
and """ quotes alone, in verbatim mode, so I could slurp in a working program, shift it over four spaces, and
have it print out, er, verbatim. And presumably in a monospace font.
The Pod format is not necessarily sufficient for writing a book. Pod is just meant to be an idiot-proof
common source for nroff, HTML, TeX, and other markup languages, as used for online documentation. Translators
exist for pod2text, pod2html, pod2man (that's for nroff(1) and troff(1)), pod2latex, and pod2fm. Various
others are available in CPAN.
Embedding Pods in Perl Modules
You can embed Pod documentation in your Perl modules and scripts. Start your documentation with an empty
line, a "=head1" command at the beginning, and end it with a "=cut" command and an empty line. Perl will
ignore the Pod text. See any of the supplied library modules for examples. If you're going to put your Pod
at the end of the file, and you're using an __END__ or __DATA__ cut mark, make sure to put an empty line there
before the first Pod command.
__END__
=head1 NAME
Time::Local - efficiently compute time from local and GMT time
Without that empty line before the "=head1", many translators wouldn't have recognized the "=head1" as
starting a Pod block.
Hints for Writing Pod
·
The podchecker command is provided for checking Pod syntax for errors and warnings. For example, it
checks for completely blank lines in Pod blocks and for unknown commands and formatting codes. You should
still also pass your document through one or more translators and proofread the result, or print out the
result and proofread that. Some of the problems found may be bugs in the translators, which you may or
may not wish to work around.
· If you're more familiar with writing in HTML than with writing in Pod, you can try your hand at writing
documentation in simple HTML, and converting it to Pod with the experimental Pod::HTML2Pod module,
(available in CPAN), and looking at the resulting code. The experimental Pod::PXML module in CPAN might
also be useful.
· Many older Pod translators require the lines before every Pod command and after every Pod command
(including "=cut"!) to be a blank line. Having something like this:
# - - - - - - - - - - - -
=item $firecracker->boom()
This noisily detonates the firecracker object.
=cut
sub boom {
...
...will make such Pod translators completely fail to see the Pod block at all.
Instead, have it like this:
separated by completely empty lines. If you have an apparently empty line with some spaces on it, this
might not count as a separator for those translators, and that could cause odd formatting.
· Older translators might add wording around an L<> link, so that "L<Foo::Bar>" may become "the Foo::Bar
manpage", for example. So you shouldn't write things like "the L<foo> documentation", if you want the
translated document to read sensibly. Instead, write "the L<Foo::Bar|Foo::Bar> documentation" or "L<the
Foo::Bar documentation|Foo::Bar>", to control how the link comes out.
· Going past the 70th column in a verbatim block might be ungracefully wrapped by some formatters.
SEE ALSO
perlpodspec, "PODs: Embedded Documentation" in perlsyn, perlnewmod, perldoc, pod2html, pod2man, podchecker.
AUTHOR
Larry Wall, Sean M. Burke
perl v5.16.3 2013-03-04 PERLPOD(1)
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