Page Source for PerlPod
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write = root
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This document is in Pod format. To read this, use a Pod formatter, like
"perldoc perlpod".
=head1 NAME
perlpod - the Plain Old Documentation format
=head1 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:
L<ordinary|/"Ordinary Paragraph">, L<verbatim|/"Verbatim
Paragraph">, and L<command|/"Command Paragraph">.
=head2 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 B<bold>,
I<italic>, C<code-style>, L<hyperlinks|perlfaq>, and
more. Such codes are explained in the "L<Formatting
Codes|/"Formatting Codes">" section, below.
=head2 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.
=head2 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:
=over
=item C<=head1 I<Heading Text>>
=item C<=head2 I<Heading Text>>
=item C<=head3 I<Heading Text>>
=item C<=head4 I<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<$/>
Such commands are explained in the "L<Formatting Codes|/"Formatting
Codes">" section, below.
=item C<=over I<indentlevel>>
=item C<=item I<stuff...>>
=item C<=back>
Item, over, and back require a little more explanation: "=over" starts
a region specifically for the generation of a list using "=item"
commands, or for indenting (groups of) normal paragraphs. At the end of
your list, use "=back" to end it. The I<indentlevel> option to
"=over" indicates how far over to indent, generally in ems (where one
em is the width of an "M" in the document's base font) or roughly
comparable units; if there is no I<indentlevel> option, it
defaults to four. (And some formatters may just ignore whatever
I<indentlevel> you provide.) In the I<stuff> in C<=item
I<stuff...>>, you may use formatting codes, as seen here:
=item Using C<$|> to Control Buffering
Such commands are explained in the "L<Formatting Codes|/"Formatting
Codes">" section, below.
Note also that there are some basic rules to using "=over" ... "=back"
regions:
=over
=item *
Don't use "=item"s outside of an "=over" ... "=back" region.
=item *
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.
=item *
Don't put "=headI<n>" commands inside an "=over" ... "=back"
region.
=item *
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.
=back
=item C<=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.)
=item C<=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 I<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
=item C<=begin I<formatname>>
=item C<=end I<formatname>>
=item C<=for I<formatname> I<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 I<formatname>", some paragraphs, and a command
"=end I<formatname>", mean that the text/data inbetween is meant
for formatters that understand the special format called
I<formatname>. For example,
=begin html
<hr> <img src="thang.png">
<p> This is a raw HTML paragraph </p>
=end html
The command "=for I<formatname> I<text...>" specifies that
the remainder of just this paragraph (starting right after
I<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 I<formatnames> will require a leading colon (as in
C<"=for :formatname">, or C<"=begin :formatname" ... "=end
:formatname">), to signal that the text is not raw data, but instead
I<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).
=back
And don't forget, when using any command, that the command lasts up
until the end of its I<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
=head2 Formatting Codes
In ordinary paragraphs and in some command paragraphs, various
formatting codes (a.k.a. "interior sequences") can be used:
=for comment
"interior sequences" is such an opaque term.
Prefer "formatting codes" instead.
=over
=item C<IE<lt>textE<gt>> -- italic text
Used for emphasis ("C<be IE<lt>careful!E<gt>>") and
parameters ("C<redo IE<lt>LABELE<gt>>")
=item C<BE<lt>textE<gt>> -- bold text
Used for switches ("C<perl's BE<lt>-nE<gt> switch>"),
programs ("C<some systems provide a BE<lt>chfnE<gt> for
that>"), emphasis ("C<be BE<lt>careful!E<gt>>"),
and so on ("C<and that feature is known as
BE<lt>autovivificationE<gt>>").
=item C<CE<lt>codeE<gt>> -- code text
Renders code in a typewriter font, or gives some other indication that
this represents program text
("C<CE<lt>gmtime($^T)E<gt>>") or some other form of
computerese ("C<CE<lt>drwxr-xr-xE<gt>>").
=item C<LE<lt>nameE<gt>> -- a hyperlink
There are various syntaxes, listed below. In the syntaxes given,
C<text>, C<name>, and C<section> cannot contain the
characters '/' and '|'; and any '<' or '>' should be matched.
=over
=item *
C<LE<lt>nameE<gt>>
Link to a Perl manual page (e.g.,
C<LE<lt>Net::PingE<gt>>). Note that C<name>
should not contain spaces. This syntax is also occasionally used for
references to UNIX man pages, as in
C<LE<lt>crontab(5)E<gt>>.
=item *
C<LE<lt>name/"sec"E<gt>> or
C<LE<lt>name/secE<gt>>
Link to a section in other manual page. E.g.,
C<LE<lt>perlsyn/"For Loops"E<gt>>
=item *
C<LE<lt>/"sec"E<gt>> or
C<LE<lt>/secE<gt>> or
C<LE<lt>"sec"E<gt>>
Link to a section in this manual page. E.g., C<LE<lt>/"Object
Methods"E<gt>>
=back
A section is started by the named heading or item. For example,
C<LE<lt>perlvar/$.E<gt>> or
C<LE<lt>perlvar/"$."E<gt>> both link to the section
started by "C<=item $.>" in perlvar. And
C<LE<lt>perlsyn/For LoopsE<gt>> or
C<LE<lt>perlsyn/"For Loops"E<gt>> both link to the
section started by "C<=head2 For Loops>" in perlsyn.
To control what text is used for display, you use
"C<LE<lt>text|...E<gt>>", as in:
=over
=item *
C<LE<lt>text|nameE<gt>>
Link this text to that manual page. E.g., C<LE<lt>Perl Error
Messages|perldiagE<gt>>
=item *
C<LE<lt>text|name/"sec"E<gt>> or
C<LE<lt>text|name/secE<gt>>
Link this text to that section in that manual page. E.g.,
C<LE<lt>SWITCH statements|perlsyn/"Basic BLOCKs and Switch
Statements"E<gt>>
=item *
C<LE<lt>text|/"sec"E<gt>> or
C<LE<lt>text|/secE<gt>> or
C<LE<lt>text|"sec"E<gt>>
Link this text to that section in this manual page. E.g.,
C<LE<lt>the various attributes|/"Member Data"E<gt>>
=back
Or you can link to a web page:
=over
=item *
C<LE<lt>scheme:...E<gt>>
Links to an absolute URL. For example,
C<LE<lt>http://www.perl.org/E<gt>>. But note that
there is no corresponding
C<LE<lt>text|scheme:...E<gt>> syntax, for various
reasons.
=back
=item C<EE<lt>escapeE<gt>> -- a character escape
Very similar to HTML/XML C<&I<foo>;> "entity
references":
=over
=item *
C<EE<lt>ltE<gt>> -- a literal E<lt> (less than)
=item *
C<EE<lt>gtE<gt>> -- a literal E<gt> (greater
than)
=item *
C<EE<lt>verbarE<gt>> -- a literal |
(I<ver>tical I<bar>)
=item *
C<EE<lt>solE<gt>> = a literal / (I<sol>idus)
The above four are optional except in other formatting codes, notably
C<LE<lt>...E<gt>>, and when preceded by a capital
letter.
=item *
C<EE<lt>htmlnameE<gt>>
Some non-numeric HTML entity name, such as
C<EE<lt>eacuteE<gt>>, meaning the same thing as
C<é> in HTML -- i.e., a lowercase e with an acute
(/-shaped) accent.
=item *
C<EE<lt>numberE<gt>>
The ASCII/Latin-1/Unicode character with that number. A leading "0x"
means that I<number> is hex, as in
C<EE<lt>0x201EE<gt>>. A leading "0" means that
I<number> is octal, as in C<EE<lt>075E<gt>>.
Otherwise I<number> is interpreted as being in decimal, as in
C<EE<lt>181E<gt>>.
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
C<EE<lt>eacuteE<gt>> as just a plain "e".)
=back
=item C<FE<lt>filenameE<gt>> -- used for filenames
Typically displayed in italics. Example:
"C<FE<lt>.cshrcE<gt>>"
=item C<SE<lt>textE<gt>> -- text contains
non-breaking spaces
This means that the words in I<text> should not be broken across
lines. Example: S<C<SE<lt>$x ? $y : $zE<gt>>>.
=item C<XE<lt>topic nameE<gt>> -- an index entry
This is ignored by most formatters, but some may use it for building
indexes. It always renders as empty-string. Example:
C<XE<lt>absolutizing relative URLsE<gt>>
=item C<ZE<lt>E<gt>> -- a null (zero-effect)
formatting code
This is rarely used. It's one way to get around using an
EE<lt>...E<gt> code sometimes. For example, instead of
"C<NEE<lt>ltE<gt>3>" (for "NE<lt>3") you could
write "C<NZE<lt>E<gt>E<lt>3>" (the
"ZE<lt>E<gt>" breaks up the "N" and the "E<lt>" so
they can't be considered the part of a (fictitious)
"NE<lt>...E<gt>" code.
=for comment
This was formerly explained as a "zero-width character". But it in
most parser models, it parses to nothing at all, as opposed to parsing
as if it were a E<zwnj> or E<zwj>, which are REAL
zero-width characters.
So "width" and "character" are exactly the wrong words.
=back
Most of the time, you will need only a single set of angle brackets to
delimit the beginning and end of formatting codes. However, sometimes
you will want to put a real right angle bracket (a greater-than sign,
'>') inside of a formatting code. This is particularly common when
using a formatting code to provide a different font-type for a snippet
of code. As with all things in Perl, there is more than one way to do
it. One way is to simply escape the closing bracket using an C<E>
code:
C<$a E<lt>=E<gt> $b>
This will produce: "C<$a E<lt>=E<gt> $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 I<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<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.
=head2 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 C<fmt> easily to reformat
them (that's F7 in my version of B<vi>, or Esc Q in my version of
B<emacs>). I wanted the translator to always leave the C<'>
and C<`> and C<"> 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 B<pod2text>, B<pod2html>, B<pod2man>
(that's for nroff(1) and troff(1)), B<pod2latex>, and
B<pod2fm>. Various others are available in CPAN.
=head2 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.
=head2 Hints for Writing Pod
=over
=item *
The B<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.
=item *
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
L<Pod::HTML2Pod|Pod::HTML2Pod> module, (available in CPAN), and
looking at the resulting code. The experimental
L<Pod::PXML|Pod::PXML> module in CPAN might also be useful.
=item *
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 {
...
=item *
Some older Pod translators require paragraphs (including command
paragraphs like "=head2 Functions") to be separated by
I<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.
=item *
Older translators might add wording around an LE<lt>E<gt>
link, so that C<LE<lt>Foo::BarE<gt>> may become "the
Foo::Bar manpage", for example. So you shouldn't write things like
C<the LE<lt>fooE<gt> documentation>, if you want the
translated document to read sensibly -- instead write C<the
LE<lt>Foo::Bar|Foo::BarE<gt> documentation> or
C<LE<lt>the Foo::Bar documentation|Foo::BarE<gt>>, to
control how the link comes out.
=item *
Going past the 70th column in a verbatim block might be ungracefully
wrapped by some formatters.
=back
=head1 SEE ALSO
L<perlpodspec>, L<perlsyn/"PODs: Embedded Documentation">,
L<perlnewmod>, L<perldoc>, L<pod2html>,
L<pod2man>, L<podchecker>.
=head1 AUTHOR
Larry Wall, Sean M. Burke
=cut