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perlpod

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, ver-
       batim, 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 justi-
       fied.

       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"
	   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 for-
	   matting 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 for-
	       matters 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 format-
	   ters that understand the special format called formatname.  For
	   example,

	     =begin html

	     
 
	     
 This is a raw HTML paragraph 

	     =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 
 
	     
 This is a raw HTML paragraph 

	   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" com-
	   mand.

	   Here are some examples of how to use these:

	     =begin html

	     
Figure 1.



	     =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 (presum-
	   ably 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 :format-
	   name", or "=begin :formatname" ... "=end :formatname"), to signal
	   that the text is not raw data, but instead is Pod text (i.e., pos-
	   sibly containing formatting codes) that's just not for normal for-
	   matting (e.g., may not be a normal-use paragraph, but might be for
	   formatting as a footnote).

       "=encoding encodingname"
	   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 or
	   Latin-1, then put a "=encoding encodingname" command early in the
	   document so that pod formatters will know how to decode the docu-
	   ment.  For encodingname, use a name recognized by the Encode::Sup-
	   ported module.  Examples:

	     =encoding utf8

	     =encoding koi8-r

	     =encoding ShiftJIS

	     =encoding big5

       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 format-
       ting codes (a.k.a. "interior sequences") can be used:

       "I" -- italic text
	   Used for emphasis (""be I"") and parameters (""redo
	   I"")

       "B" -- bold text
	   Used for switches (""perl's B<-n> switch""), programs (""some sys-
	   tems provide a B for that""), emphasis (""be B""),
	   and so on (""and that feature is known as B"").

       "C" -- code text
	   Renders code in a typewriter font, or gives some other indication
	   that this represents program text (""C"") or some
	   other form of computerese (""C"").

       "L" -- 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"

	       Link to a Perl manual page (e.g., "L").  Note that
	       "name" should not contain spaces.  This syntax is also occa-
	       sionally used for references to UNIX man pages, as in
	       "L".

	   *   "L" or "L"

	       Link to a section in other manual page.	E.g., "L"

	   *   "L" or "L" or "L<"sec">"

	       Link to a section in this manual page.  E.g., "L"

	   A section is started by the named heading or item.  For example,
	   "L" or "L" both link to the section
	   started by ""=item $."" in perlvar.	And "L" or
	   "L" both link to the section started by
	   ""=head2 For Loops"" in perlsyn.

	   To control what text is used for display, you use ""L"",
	   as in:

	   *   "L"

	       Link this text to that manual page.  E.g., "L"

	   *   "L" or "L"

	       Link this text to that section in that manual page.  E.g.,
	       "L"

	   *   "L" or "L" or "L"

	       Link this text to that section in this manual page.  E.g.,
	       "L"

	   Or you can link to a web page:

	   *   "L"

	       Links to an absolute URL.  For example,
	       "L".  But note that there is no corre-
	       sponding "L" syntax, for various reasons.

       "E" -- a character escape
	   Very similar to HTML/XML "&foo;" "entity references":

	   *   "E" -- a literal < (less than)

	   *   "E" -- a literal > (greater than)

	   *   "E" -- a literal | (vertical bar)

	   *   "E" = a literal / (solidus)

	       The above four are optional except in other formatting codes,
	       notably "L<...>", and when preceded by a capital letter.

	   *   "E"

	       Some non-numeric HTML entity name, such as "E", meaning
	       the same thing as "é" in HTML -- i.e., a lowercase e
	       with an acute (/-shaped) accent.

	   *   "E"

	       The ASCII/Latin-1/Unicode character with that number.  A lead-
	       ing "0x" means that number is hex, as in "E<0x201E>".  A lead-
	       ing "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 ren-
	       der characters above 255.  (Some formatters may even have to
	       use compromised renderings of Latin-1 characters, like render-
	       ing "E" as just a plain "e".)

       "F" -- used for filenames
	   Typically displayed in italics.  Example: ""F<.cshrc>""

       "S" -- text contains non-breaking spaces
	   This means that the words in text should not be broken across
	   lines.  Example: "S<$x ? $y : $z>".

       "X" -- an index entry
	   This is ignored by most formatters, but some may use it for build-
	   ing indexes.  It always renders as empty-string.  Example: "X"

       "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 ""NE3"" (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=E $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=E $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:

	   CEthing.dat") || die $!>
	   C<$foo-Ebar();>

       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 presum-
       ably 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.  Transla-
       tors 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


       o   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 trans-
	   lators and proofread the result, or print out the result and proof-
	   read that.  Some of the problems found may be bugs in the transla-
	   tors, which you may or may not wish to work around.

       o   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 mod-
	   ule, (available in CPAN), and looking at the resulting code.  The
	   experimental Pod::PXML module in CPAN might also be useful.

       o   Many older Pod translators require the lines before every Pod com-
	   mand 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 {
	    ...

       o   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.

       o   Older translators might add wording around an L<> link, so that
	   "L" may become "the Foo::Bar manpage", for example.  So
	   you shouldn't write things like "the L documentation", if you
	   want the translated document to read sensibly -- instead write "the
	   L documentation" or "L", to control how the link comes out.

       o   Going past the 70th column in a verbatim block might be ungrace-
	   fully wrapped by some formatters.

SEE ALSO
       perlpodspec, "PODs: Embedded Documentation" in perlsyn, perlnewmod,
       perldoc, pod2html, pod2man, podchecker.

AUTHOR
       Larry Wall, Sean M. Burke



perl v5.8.8			  2006-01-07			    PERLPOD(1)