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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
=head1 Heading Text
=head2 Heading Text
=head3 Heading Text
=head4 Heading Text
=over indentlevel
=item stuff
=back
=cut
=pod
=begin format
=end format
=for format text...
To explain them each in detail:
"=head1 Heading Text"
"=head2 Heading Text"
"=head3 Heading Text"
"=head4 Heading Text"
Head1 through head4 produce headings, head1 being the highest level.
The text in the rest of this paragraph is the content of the heading.
For example:
=head2 Object Attributes
The text "Object Attributes" comprises the heading there. (Note that
head3 and head4 are recent additions, not supported in older Pod
translators.) The text in these heading commands can use formatting
codes, as seen here:
=head2 Possible Values for C<$/>
Such commands are explained in the "Formatting Codes" section, below.
"=over indentlevel"
"=item stuff..."
"=back"
Item, over, and back require a little more explanation: "=over" starts
a region specifically for the generation of a list using "=item"
commands, or for indenting (groups of) normal paragraphs. At the end
of your list, use "=back" to end it. The indentlevel option to "=over"
indicates how far over to indent, generally in ems (where one em is the
width of an "M" in the document's base font) or roughly comparable
units; if there is no indentlevel option, it defaults to four. (And
some formatters may just ignore whatever indentlevel you provide.) In
the stuff in "=item stuff...", you may use formatting codes, as seen
here:
=item Using C<$|> 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
Remember to check its return value, as in:
stuff() || die "Couldn't do stuff!";
=cut
"=begin formatname"
"=end formatname"
"=for formatname text..."
For, begin, and end will let you have regions of text/code/data that
are not generally interpreted as normal Pod text, but are passed
directly to particular formatters, or are otherwise special. A
formatter 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 inbetween 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
inbetween. (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 :formatname"), to
signal that the text is not raw data, but instead is Pod text (i.e.,
possibly containing formatting codes) that's just not for normal
formatting (e.g., may not be a normal-use paragraph, but might be for
formatting as a footnote).
And don't forget, when using any 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($^T)>"") or some other form of
computerese (""C<drwxr-xr-x>"").
"L<name>" -- a hyperlink
There are various syntaxes, listed below. In the syntaxes given,
"text", "name", and "section" cannot contain the characters '/' and
'|'; and any '<' or '>' should be matched.
· "L<name>"
Link to a Perl manual page (e.g., "L<Net::Ping>"). Note that
"name" should not contain spaces. This syntax is also occasionally
used for references to UNIX man pages, as in "L<crontab(5)>".
· "L<name/"sec">" or "L<name/sec>"
Link to a section in other manual page. E.g., "L<perlsyn/"For
Loops">"
· "L</"sec">" or "L</sec>" or "L<"sec">"
Link to a section in this manual page. E.g., "L</"Object
Methods">"
A section is started by the named heading or item. For example,
"L<perlvar/$.>" 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<SWITCH statements|perlsyn/"Basic BLOCKs and Switch Statements">"
· "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:...>"
Links to an absolute URL. For example, "L<http://www.perl.org/>".
But note that there is no corresponding "L<text|scheme:...>"
syntax, for various reasons.
"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 "E<0x201E>". A leading "0"
means that number is octal, as in "E<075>". Otherwise number is
interpreted as being in decimal, as in "E<181>".
Note that older Pod formatters might not recognize octal or hex
numeric escapes, and that many formatters cannot reliably render
characters above 255. (Some formatters may even have to use
compromised renderings of Latin-1 characters, like rendering
"E<eacute>" as just a plain "e".)
"F<filename>" -- used for filenames
Typically displayed in italics. Example: ""F<.cshrc>""
"S<text>" -- text contains non-breaking spaces
This means that the words in text should not be broken across lines.
Example: "S<$x ? $y : $z>".
"X<topic name>" -- an index entry
This is ignored by most formatters, but some may use it for building
indexes. It always renders as empty-string. Example: "X<absolutizing
relative URLs>"
"Z<>" -- a null (zero-effect) formatting code
This is rarely used. It's one way to get around using an E<...> code
sometimes. For example, instead of ""NE<lt>3"" (for "N<3") you could
write ""NZ<><3"" (the "Z<>" breaks up the "N" and the "<" so they can't
be considered the part of a (fictitious) "N<...>" code.
Most of the time, you will need only a single set of angle brackets to
delimit the beginning and end of formatting codes. However, sometimes you
will want to put a real right angle bracket (a greater-than sign, '>')
inside of a formatting code. This is particularly common when using a
formatting code to provide a different font-type for a snippet of code. As
with all things in Perl, there is more than one way to do it. One way is
to simply escape the closing bracket using an "E" code:
C<$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. With the Pod
formatters that are standard starting with perl5.5.660, 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>
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(); >>
which is presumably easier to read than the old way:
C<open(X, "E<gt>E<gt>thing.dat") || die $!>
C<$foo-E<gt>bar(); >>
This is currently supported by pod2text (Pod::Text), pod2man (Pod::Man),
and any other pod2xxx or Pod::Xxxx translators that use Pod::Parser 1.093
or later, or Pod::Tree 1.02 or later.
The Intent
The intent is simplicity of use, not power of expression. Paragraphs look
like paragraphs (block format), so that they stand out visually, and so
that I could run them through "fmt" easily to reformat them (that's F7 in
my version of vi, or Esc Q in my version of emacs). I wanted the
translator to always leave the "'" and "`" 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:
# - - - - - - - - - - - -
=item $firecracker->boom()
This noisily detonates the firecracker object.
=cut
sub boom {
...
· Some older Pod translators require paragraphs (including command
paragraphs like "=head2 Functions") to be 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
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Index for
Section 1 |
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Alphabetical
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Top of
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