PERLPOD(1) Perl Programmers Reference Guide PERLPOD(1) #
PERLPOD(1) Perl Programmers Reference Guide PERLPOD(1)
NNAAMMEE #
perlpod - the Plain Old Documentation format
DDEESSCCRRIIPPTTIIOONN #
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.
OOrrddiinnaarryy PPaarraaggrraapphh 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 bboolldd, _i_t_a_l_i_c,
"code-style", hyperlinks, and more. Such codes are explained in the
"Formatting Codes" section, below.
VVeerrbbaattiimm PPaarraaggrraapphh 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.
CCoommmmaanndd PPaarraaggrraapphh 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
=head5 Heading Text
=head6 Heading Text
=over indentlevel
=item stuff
=back
=begin format
=end format
=for format text...
=encoding type
=cut
To explain them each in detail:
"=head1 _H_e_a_d_i_n_g _T_e_x_t"
"=head2 _H_e_a_d_i_n_g _T_e_x_t"
"=head3 _H_e_a_d_i_n_g _T_e_x_t"
"=head4 _H_e_a_d_i_n_g _T_e_x_t"
"=head5 _H_e_a_d_i_n_g _T_e_x_t"
"=head6 _H_e_a_d_i_n_g _T_e_x_t"
Head1 through head6 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. The text
in these heading commands can use formatting codes, as seen here:
=head2 Possible Values for C<$/>
Such commands are explained in the "Formatting Codes" section, below.
Note that "head5" and "head6" were introduced in 2020 and in
Pod::Simple 3.41, released in October 2020, so they might not be
supported on the Pod parser you use.
"=over _i_n_d_e_n_t_l_e_v_e_l"
"=item _s_t_u_f_f_._._."
"=back"
Item, over, and back require a little more explanation: "=over"
starts a region specifically for the generation of a list using
"=item" commands, or for indenting (groups of) normal paragraphs. At
the end of your list, use "=back" to end it. The _i_n_d_e_n_t_l_e_v_e_l option
to "=over" indicates how far over to indent, generally in ems (where
one em is the width of an "M" in the document's base font) or roughly
comparable units; if there is no _i_n_d_e_n_t_l_e_v_e_l option, it defaults to
four. (And some formatters may just ignore whatever _i_n_d_e_n_t_l_e_v_e_l you
provide.) In the _s_t_u_f_f in "=item _s_t_u_f_f_._._.", you may use formatting
codes, as seen here:
=item Using C<$|> 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 "=head_n" 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 have a list that contains both: 1)
things that don't look like bullets nor numbers, plus 2) things
that do, you should preface the bullet- or number-like items with
"Z<>". See Z<> below for an example.)
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 _a_n_y 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 _f_o_r_m_a_t_n_a_m_e"
"=end _f_o_r_m_a_t_n_a_m_e"
"=for _f_o_r_m_a_t_n_a_m_e _t_e_x_t_._._."
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 _f_o_r_m_a_t_n_a_m_e", some paragraphs, and a command "=end
_f_o_r_m_a_t_n_a_m_e", mean that the text/data in between is meant for
formatters that understand the special format called _f_o_r_m_a_t_n_a_m_e. For
example,
=begin html
<hr> <img src="thang.png">
<p> This is a raw HTML paragraph </p>
=end html
The command "=for _f_o_r_m_a_t_n_a_m_e _t_e_x_t_._._." specifies that the remainder of
just this paragraph (starting right after _f_o_r_m_a_t_n_a_m_e) 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 _f_o_r_m_a_t_n_a_m_e_s 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 _i_s 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).
"=encoding _e_n_c_o_d_i_n_g_n_a_m_e"
This command is used for declaring the encoding of a document. Most
users won't need this; but if your encoding isn't US-ASCII, then put
a "=encoding _e_n_c_o_d_i_n_g_n_a_m_e" command very early in the document so that
pod formatters will know how to decode the document. For
_e_n_c_o_d_i_n_g_n_a_m_e, use a name recognized by the Encode::Supported module.
Some pod formatters may try to guess between a Latin-1 or CP-1252
versus UTF-8 encoding, but they may guess wrong. It's best to be
explicit if you use anything besides strict ASCII. Examples:
=encoding latin1
=encoding utf8
=encoding koi8-r
=encoding ShiftJIS
=encoding big5
"=encoding" affects the whole document, and must occur only once.
And don't forget, all commands but "=encoding" last up until the end of
its _p_a_r_a_g_r_a_p_h, not its line. So in the examples below, you can see that
every command needs the blank line after it, to end its paragraph. (And
some older Pod translators may require the "=encoding" line to have a
following blank line as well, even though it should be legal to omit.)
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
FFoorrmmaattttiinngg CCooddeess 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
"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($^T)>"") or some other
form of computerese (""C<drwxr-xr-x>"").
"L<name>" -- a hyperlink
There are various syntaxes, listed below. In the syntaxes given,
"text", "name", and "section" cannot contain the characters '/' and
'|'; and any '<' or '>' should be matched.
• "L<name>"
Link to a Perl manual page (e.g., "L<Net::Ping>"). Note that
"name" should not contain spaces. This syntax is also
occasionally used for references to Unix man pages, as in
"L<crontab(5)>".
• "L<name/"sec">" or "L<name/sec>"
Link to a section in other manual page. E.g., "L<perlsyn/"For
Loops">"
• "L</"sec">" or "L</sec>"
Link to a section in this manual page. E.g., "L</"Object
Methods">"
A section is started by the named heading or item. For example,
"L<perlvar/$.>" 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 "&_f_o_o;" "entity references":
• "E<lt>" -- a literal < (less than)
• "E<gt>" -- a literal > (greater than)
• "E<verbar>" -- a literal | (_v_e_rtical _b_a_r)
• "E<sol>" -- a literal / (_s_o_lidus)
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 _n_u_m_b_e_r is hex, as in "E<0x201E>". A leading "0"
means that _n_u_m_b_e_r is octal, as in "E<075>". Otherwise _n_u_m_b_e_r 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/CP-1252 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 _t_e_x_t should not be broken across lines.
Example: "S<$x ? $y : $z>".
"X<topic name>" -- an index entry
This is ignored by most formatters, but some may use it for building
indexes. It always renders as empty-string. Example:
"X<absolutizing relative URLs>"
"Z<>" -- a null (zero-effect) formatting code
This is rarely used. It's one way to get around using an E<...> code
sometimes. For example, instead of ""NE<lt>3"" (for "N<3") you could
write ""NZ<><3"" (the "Z<>" breaks up the "N" and the "<" so they
can't be considered the part of a (fictitious) "N<...>" code).
Another use is to indicate that _s_t_u_f_f in "=item Z<>_s_t_u_f_f_._._." is not
to be considered to be a bullet or number. For example, without the
"Z<>", the line
=item Z<>500 Server error
could possibly be parsed as an item in a numbered list when it isn't
meant to be.
Still another use is to maintain visual space between "=item" lines.
If you specify
=item foo
=item bar
it will typically get rendered as
foo
bar
That may be what you want, but if what you really want is
foo
bar
you can use "Z<>" to accomplish that
=item foo
Z<> #
=item bar
Most of the time, you will need only a single set of angle brackets to
delimit the beginning and end of formatting codes. However, sometimes
you will want to put a real right angle bracket (a greater-than sign,
'>') inside of a formatting code. This is particularly common when using
a formatting code to provide a different font-type for a snippet of code.
As with all things in Perl, there is more than one way to do it. One way
is to simply escape the closing bracket using an "E" code:
C<$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 _i_f _a_n_d _o_n_l_y _i_f _t_h_e_r_e _i_s
_w_h_i_t_e_s_p_a_c_e _r_i_g_h_t _a_f_t_e_r _t_h_e _o_p_e_n_i_n_g _d_e_l_i_m_i_t_e_r _a_n_d _w_h_i_t_e_s_p_a_c_e _r_i_g_h_t _b_e_f_o_r_e
_t_h_e _c_l_o_s_i_n_g _d_e_l_i_m_i_t_e_r_! 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(); >>
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.
TThhee IInntteenntt 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 vvii, or Esc Q in my version of eemmaaccss). 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 ppoodd22tteexxtt, ppoodd22hhttmmll, ppoodd22mmaann (that's for nnrrooffff(1) and ttrrooffff(1)),
ppoodd22llaatteexx, and ppoodd22ffmm. Various others are available in CPAN.
EEmmbbeeddddiinngg PPooddss iinn PPeerrll MMoodduulleess 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. The ppeerrll executable will ignore the Pod text. You can place a Pod statement where ppeerrll expects the beginning of a new statement, but not within a statement, as that would result in an error. 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.
HHiinnttss ffoorr WWrriittiinngg PPoodd •
The ppooddcchheecckkeerr 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 _c_o_m_p_l_e_t_e_l_y
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.
SSEEEE AALLSSOO #
perlpodspec, "PODs: Embedded Documentation" in perlsyn, perlnewmod,
perldoc, pod2html, pod2man, podchecker.
AAUUTTHHOORR #
Larry Wall, Sean M. Burke
perl v5.36.3 2023-02-15 PERLPOD(1)