perlpod - 明瞭的古式文書書式

目次

名前

perlpod - 明瞭的古式文書書式

説明

Pod は, 手軽に使えるマークアップ言語です. Perl 及び Perl プログラム, Perl モジュールのドキュメントを書くために使われています.

Pod からプレインテキストやHTML, マニュアルページといった他のいろいろな フォーマットに変換する翻訳器もあります.

Pod のマークアップは３つの基本的な段落から構成されています: "通常段落" 及び "直述段落", "コマンド段落".

通常段落

ドキュメント内のほとんどの段落は, この段落のような, テキストから成る 普通のブロックでしょう. なんのマークアップも使わずに単純にテキストを 入力し, そしてその前後に空行を入れることでブロックとなります. これは, 最適な改行を施され, 可変長フォントで均等割り付けされる 最小限の整形が行われるでしょう,

通常段落の中でも, 太字, 斜体, コードスタイル, hyperlinks のような整形を利用できます. これらに関しては後ほど "整形コード" で説明します.

直述段落

直述段落(Verbatim Paragraph)は通常コードブロックやそれ以外の, 特別な パースやフォーマットを必要としない, もしくは折り返しすべきではない テキストを表現するために利用されます.

直述段落は空白もしくはタブ文字で始まる点で識別されます. (そして多くの 場合, 全ての行がスペースやタブで始まっているでしょう.) このとき タブは8カラム境界と仮定してそのまま再現されるでしょう. そして 特殊な整形コードは無いため斜体やその他の装飾は利用できません. \ はあくまで \ でありそれ以外の何者でもありません.

コマンド段落

コマンド段落はテキスト塊全体に特別な処理をするために使われます. 見出しやリスト項目などです.

全てのコマンド段落は(一般的に１行からなり) "=" から始まり, それに識別子, そしてコマンドに必要であれば任意でテキストが続きます. 

    =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

    =head1 見出し文
    =head2 見出し文
    =head3 見出し文
    =head4 見出し文
    =over インデントレベル
    =item 項目
    =back
    =cut
    =pod
    =begin フォーマット
    =end フォーマット
    =for フォーマット テキスト...

詳細は以下になります:

=head1 見出し文
=head2 見出し文
=head3 見出し文
=head4 見出し文

head1 から head4 は見出しを生成します. head1 が一番大きくなります. この段落の残りの文は見出しの内容です. 例: 

  =head2 Object Attributes

  =head2 オブジェクトの属性

文 "オブジェクトの属性" はこの見出しを形成します. (ただ, head3 と head4 は 最近追加されたものなので古い Pod トランスレータはサポートしていないかも しれません.) これらの見出しコマンドのテキストには次にあげるように 整形符号を使うこともできます: 

  =head2 Possible Values for C<$/>

  =head2 C<$/> に有効な値

この様なコマンドについては, 後述の "整形符号" 節で説明します.

=over インデントレベル
=item 項目...
=back

item, over, back には少々説明が必要です: "=over" はある領域, 特に "=item" コマンドを使うリストを生成する領域, もしくは通常段落(のグループ) のインデントのための領域を開始します. リストの最後では, 領域を完了するために "=back" を使います. "=over" のインデントレベル オプションはどのくらい インデントするのかを, 通常 em 単位(1emはドキュメントの基本フォントでの "M" の 幅です)もしくは大雑把に互換性のありそうな単位で指定します. もし インデントレベル オプションが指定されていなければそのデフォルト値は 4 です. (また, いくつかのフォーマッタは インデントレベル に与えられている 指定をあっさり無視するでしょう.) =item 項目... の 項目 には 次にあげるように整形符号を使うことができます: 

  =item Using C<$|> to Control Buffering

  =item C<$|> を使ってバッファリングを制御する

この様なコマンドについては, 後述の "整形符号" 節で説明します.

以下にあげる "=over" ... "=back" 領域を使うためのいくつかの基本的なルールも 参考にしてください:

=cut

Pod ブロックの終了を指定します. 空行, そして "=cut" から始まる行, そしてその後に空行を記述しなさい. これは Perl (及び Pod フォーマッタ)に ここが Perl コードが再開される場所であることを知らせます. ("=cut" の前の空行は技術的には必要ではありませんが, 多くの古い Pod プロセッサはこれを必要とします.

=pod

"=pod" コマンド自身はなにもしませんが, これは Perl (及び Pod フォーマッタ)に ここから Pod ブロックが始まっていることを通知します. Pod ブロックはどの コマンド段落からでも始めることができます. このため "=pod" コマンドはたいてい Pod ブロックを通常段落や直述段落から始めたいときにのみ使われます. 

  =item stuff()

  This function does stuff.

  この関数はなにかします. 

  =cut

  sub stuff {
    ...
  }

  =pod

  Remember to check its return value, as in:

  復帰値の確認を忘れないように:

    stuff() || die "Couldn't do stuff!";

  =cut
=begin フォーマット名
=end フォーマット名
=for フォーマット名 文...

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).

=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 document. For encodingname, use a name recognized by the Encode::Supported 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 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.

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:

Or you can link to a web page:

E<escape> -- a character escape

Very similar to HTML/XML &foo; "entity references":

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.

関連項目

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

著者

Larry Wall, Sean M. Burke

perlpod - 明瞭的古式文書書式

索引

perlpod - 明瞭的古式文書書式