perlrebackslash.podの翻訳（途中）
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=encoding utf8 =head1 NAME =begin original perlrebackslash - Perl Regular Expression Backslash Sequences and Escapes =end original perlrebackslash - Perl 正規表現でのバックスラッシュシーケンスとエスケープ =head1 DESCRIPTION =begin original The top level documentation about Perl regular expressions is found in L<perlre>. =end original Perl の正規表現についての最上位のドキュメントは、L<perlre> にあります。 =begin original This document describes all backslash and escape sequences. After explaining the role of the backslash, it lists all the sequences that have a special meaning in Perl regular expressions (in alphabetical order), then describes each of them. =end original このドキュメントでは、全てのバックスラッシュとエスケープ・シーケンスについて記述します。 バックスラッシュの役割について説明したあと、Perl の正規表現で特別な意味を持つシーケンスを(アルファベット順に)全て列挙し、 それぞれについて解説します。 =begin original Most sequences are described in detail in different documents; the primary purpose of this document is to have a quick reference guide describing all backslash and escape sequences. =end original ほとんどのシーケンスは、その詳細が異なるドキュメント中に記述されています。 このドキュメントの主な目的は、 全てのバックスラッシュとエスケープ・シーケンスについて説明する、 クイック・リファレンス・ガイドを提供することです。 =head2 The backslash =begin original In a regular expression, the backslash can perform one of two tasks: it either takes away the special meaning of the character following it (for instance, C<\|> matches a vertical bar, it's not an alternation), or it is the start of a backslash or escape sequence. =end original 正規表現中では、バックスラッシュは二つの役割のうちのひとつ: バックスラッシュに続く文字の特別な意味を消し去る (例えば、C<\|> は水平バーにマッチし。選択ではありません)か、 バックスラッシュシーケンスまたはエスケープ・シーケンスを開始する、 のどちらかを行います。 =begin original The rules determining what it is are quite simple: if the character following the backslash is an ASCII punctuation (non-word) character (that is, anything that is not a letter, digit or underscore), then the backslash just takes away the special meaning (if any) of the character following it. =end original バックスラッシュがどちらの役割を持っているのかを決めるルールは簡単です: もしバックスラッシュの後ろの文字が ASCII 記号文字 (普通の文字でも、数字でも、アンダースコアでもない文字どれでも) なら、バックスラッシュは単にその文字の特別な意味を取り去ります。 =begin original If the character following the backslash is an ASCII letter or an ASCII digit, then the sequence may be special; if so, it's listed below. A few letters have not been used yet, so escaping them with a backslash doesn't change them to be special. A future version of Perl may assign a special meaning to them, so if you have warnings turned on, Perl will issue a warning if you use such a sequence. [1]. =end original もしバックスラッシュの後ろの文字が普通の ASCII 文字か、ASCII の数字なら、 シーケンスは下に列挙してあるような、特別な意味を持っているかもしれません。 何種類かの文字は、まだ使われていません。 シーケンスとしてまだ使われていない文字を、バックスラッシュでエスケープしても、 それは特別な意味を持ちません。 これらの文字は、Perl 将来のバージョンで特別な意味を付与されるかもしれません。 もしあなたが warnings を有効にしていれば、Perl はこのようなシーケンスの使用に対し、警告を発します。 [1]. =begin original It is however guaranteed that backslash or escape sequences never have a punctuation character following the backslash, not now, and not in a future version of Perl 5. So it is safe to put a backslash in front of a non-word character. =end original しかし、バックスラッシュ・シーケンスやエスケープ・シーケンスとして、 バックスラッシュの後ろに記号文字が来る形が使われることはないと、現在、また将来の Perl 5 においても保証されています。 ですから、記号文字の前にバックスラッシュを置くことは安全です。 =begin original Note that the backslash itself is special; if you want to match a backslash, you have to escape the backslash with a backslash: C</\\/> matches a single backslash. =end original バックスラッシュはそれ自身が特別であることに注意してください。 もしバックスラッシュにマッチさせたいなら、 バックスラッシュをバックスラッシュでエスケープしなければいけません。 つまり C</\\/> は、ひとつのバックスラッシュにマッチします。 =over 4 =item [1] =begin original There is one exception. If you use an alphanumerical character as the delimiter of your pattern (which you probably shouldn't do for readability reasons), you will have to escape the delimiter if you want to match it. Perl won't warn then. See also L<perlop/Gory details of parsing quoted constructs>. =end original 例外がひとつあります。もし、 (読みやすさを保つために、たぶんこういうことはするべきではないでしょうが) 英数字をパターンのデリミタとして使用しているなら、 デリミタの文字にマッチさせるためには、それをエスケープする必要があります。 これに関しては Perl は警告をしません。 L<perlop/Gory details of parsing quoted constructs> も見てください。 =back =head2 All the sequences and escapes =begin original Those not usable within a bracketed character class (like C<[\da-z]>) are marked as C<Not in [].> =end original 文字クラス (C<[\da-z]> のようなもの) のブラケットの中では使用できないものについては C<Not in [].> とマークしてあります。 =begin original \000 Octal escape sequence. \1 Absolute backreference. Not in []. \a Alarm or bell. \A Beginning of string. Not in []. \b Word/non-word boundary. (Backspace in []). \B Not a word/non-word boundary. Not in []. \cX Control-X \C Single octet, even under UTF-8. Not in []. \d Character class for digits. \D Character class for non-digits. \e Escape character. \E Turn off \Q, \L and \U processing. Not in []. \f Form feed. \g{}, \g1 Named, absolute or relative backreference. Not in []. \G Pos assertion. Not in []. \h Character class for horizontal whitespace. \H Character class for non horizontal whitespace. \k{}, \k<>, \k'' Named backreference. Not in []. \K Keep the stuff left of \K. Not in []. \l Lowercase next character. Not in []. \L Lowercase till \E. Not in []. \n (Logical) newline character. \N Any character but newline. Experimental. Not in []. \N{} Named or numbered (Unicode) character. \p{}, \pP Character with the given Unicode property. \P{}, \PP Character without the given Unicode property. \Q Quotemeta till \E. Not in []. \r Return character. \R Generic new line. Not in []. \s Character class for whitespace. \S Character class for non whitespace. \t Tab character. \u Titlecase next character. Not in []. \U Uppercase till \E. Not in []. \v Character class for vertical whitespace. \V Character class for non vertical whitespace. \w Character class for word characters. \W Character class for non-word characters. \x{}, \x00 Hexadecimal escape sequence. \X Unicode "extended grapheme cluster". Not in []. \z End of string. Not in []. \Z End of string. Not in []. =end original \000 8進数エスケープ・シーケンス \1 絶対後方参照 Not in []. \a アラームまたはベル \A 文字列の先頭 Not in []. \b 単語境界 (文字クラス [] の中ではバックスペース) \B 非単語境界 Not in []. \cX Control-X \C ひとつのオクテット、UTF-8 であっても Not in []. \d 数字を表す文字クラス \D 非数字を表す文字クラス \e エスケープ文字 \E \Q, \L, \U 処理の停止 Not in []. \f フォームフィード \g{}, \g1 名前つき、絶対、相対後方参照 Not in []. \G Pos 表明 Not in []. \h 水平空白を表す文字クラス \H 水平空白以外を表す文字クラス \k{}, \k<>, \k'' 名前つき後方参照 Not in []. \K \K の左側の内容を保存する Not in []. \l 次の文字を小文字にします Not in []. \L \E まで小文字にします Not in []. \n (論理) 改行文字 \N 改行文字以外 実験的 Experimental. Not in []. \N{} 名前つき文字 or numbered (Unicode) character. \p{}, \pP Unicode プロパティにマッチする文字 \P{}, \PP Unicode プロパティにマッチする文字以外の文字 \Q \E までのメタ文字をクォートする Not in []. \r リターン文字 \R 一般的な改行 Not in []. \s 空白文字を表す文字クラス \S 非空白文字を表す文字クラス \t タブ \u 次の文字をタイトル文字にする Not in []. \U \E までの文字を大文字にする Not in []. \v 垂直空白を表す文字クラス \V 非垂直空白を表す文字クラス \w 単語文字を表す文字クラス \W 非単語文字を表す文字クラス \x{}, \x00 16進値 \X 拡張された Unicode の結合文字 Not in []. \z 文字列の末尾 Not in []. \Z 文字列の本当の末尾 Not in []. =head2 Character Escapes =head3 Fixed characters =begin original A handful of characters have a dedicated I<character escape>. The following table shows them, along with their ASCII code points (in decimal and hex), their ASCII name, the control escape on ASCII platforms and a short description. (For EBCDIC platforms, see L<perlebcdic/OPERATOR DIFFERENCES>.) =end original いくつかの文字にはI<文字エスケープ>が用意されています。 ASCII コードポイント (10進、16進)、ASCII 名、ASCII プラットフォームにおけるコントロールエスケープと短い説明を添えて、下に示します。 (EBCDIC プラットフォームについては、L<perlebcdic/OPERATOR DIFFERENCES> を見てください。) =begin original Seq. Code Point ASCII Cntrl Description. Dec Hex \a 7 07 BEL \cG alarm or bell \b 8 08 BS \cH backspace [1] \e 27 1B ESC \c[ escape character \f 12 0C FF \cL form feed \n 10 0A LF \cJ line feed [2] \r 13 0D CR \cM carriage return \t 9 09 TAB \cI tab =end original Seq. Code Point ASCII Cntrl Description. Dec Hex \a 7 07 BEL \cG アラーム、またはベル \b 8 08 BS \cH バックスペース [1] \e 27 1B ESC \c[ エスケープ文字 \f 12 0C FF \cL フォームフィード \n 10 0A LF \cJ ラインフィード [2] \r 13 0D CR \cM キャリッジリターン \t 9 09 TAB \cI タブ =over 4 =item [1] =begin original C<\b> is the backspace character only inside a character class. Outside a character class, C<\b> is a word/non-word boundary. =end original C<\b> は文字クラスの中ある場合にだけ、バックスペースを表します。 文字クラスの外では、C<\b> は単語境界を表します。 =item [2] =begin original C<\n> matches a logical newline. Perl will convert between C<\n> and your OS's native newline character when reading from or writing to text files. =end original C<\n> は論理改行にマッチします。Perl は、テキストファイルの読み書きの際に、C<\n> とあなたの OS のネイティブの改行文字を変換します。 =back =head4 Example =begin original $str =~ /\t/; # Matches if $str contains a (horizontal) tab. =end original $str =~ /\t/; # $str が(水平)タブを含んでいればマッチ =head3 Control characters =begin original C<\c> is used to denote a control character; the character following C<\c> determines the value of the construct. For example the value of C<\cA> is C<chr(1)>, and the value of C<\cb> is C<chr(2)>, etc. The gory details are in L<perlop/"Regexp Quote-Like Operators">. A complete list of what C<chr(1)>, etc. means for ASCII and EBCDIC platforms is in L<perlebcdic/OPERATOR DIFFERENCES>. =end original C<\c> はコントロール文字を示すのに使われます。C<\c> の後ろの文字が作られる値を決めます。例えば、C<\cA> は C<chr(1)> であり、C<\cb> は C<char(2)> であり、等々。血みどろの詳細は L<perlop/"Regexp Quote-Like Operators"> にあります。ASCII と EBCDIC プラットフォームで C<chr(1)> 等が何を意味するかの完全なリストは L<perlebcdic/OPERATOR DIFFERENCES> にあります。 =begin original Note that C<\c\> alone at the end of a regular expression (or doubled-quoted string) is not valid. The backslash must be followed by another character. That is, C<\c\I<X>> means C<chr(28) . 'I<X>'> for all characters I<X>. =end original 正規表現（と、ダブルクォート文字）の最後に単独の C<\c\> を置くのは正しくありません。 バックスラッシュには、なにか他の文字が続かなければなりません。 I<X> がどんな文字であろうと、C<\c\I<X>> は C<chr(28) . 'I<X>'> を意味します。 =begin original To write platform-independent code, you must use C<\N{I<NAME>}> instead, like C<\N{ESCAPE}> or C<\N{U+001B}>, see L<charnames>. =end original プラットフォーム独立なコードを書くには、C<\N{ESCAPE}> や C<\N{U+001B}> のように C<\N{I<NAME>}> を使わなければなりません。 L<charnames> を見てください。 =begin original Mnemonic: I<c>ontrol character. =end original 覚え方: I<c> はコントロール (I<c>ontrol) の頭文字。 =head4 Example =begin original $str =~ /\cK/; # Matches if $str contains a vertical tab (control-K). =end original $str =~ /\cK/; # もし $str が垂直タブ (control-K) を含んでいればマッチ =head3 Named or numbered characters =begin original Unicode characters have a Unicode name and numeric ordinal value. Use the C<\N{}> construct to specify a character by either of these values. =end original Unicode 文字は、Unicode 名と序数値を持っています。 このどちらかの値で文字を指定するには C<\N{}> を使ってください。 =begin original To specify by name, the name of the character goes between the curly braces. In this case, you have to C<use charnames> to load the Unicode names of the characters, otherwise Perl will complain. =end original 名前で指定するには、カーリーブラケットの間に文字の名前をおきます。 この場合、文字の Unicode 名をロードするために C<use charnames> しなければなりません。 これを怠ると、Perl は文句を言うでしょう。 =begin original To specify by Unicode ordinal number, use the form C<\N{U+I<wide hex character>}>, where I<wide hex character> is a number in hexadecimal that gives the ordinal number that Unicode has assigned to the desired character. It is customary (but not required) to use leading zeros to pad the number to 4 digits. Thus C<\N{U+0041}> means C<Latin Capital Letter A>, and you will rarely see it written without the two leading zeros. C<\N{U+0041}> means "A" even on EBCDIC machines (where the ordinal value of "A" is not 0x41). =end original Unicode 序数値で指定するには、C<\N{U+I<wide hex character>}> の形式を使用します。 I<wide hex character> の部分は、必要としている文字がアサインされている 16 進の序数値です。 数値は、ゼロによるパディングをおこなって 4 桁にそろえるのが習慣です。(必須ではありません。) 従って C<\N{U+0041}> は C<Latin Capital Letter A> を意味します。 先行する 2 つのゼロを持たない書き方を目にすることは、めったにないでしょう。 C<\N{U+0041}> は EBCDIC マシンにおいてさえ "A" を意味します。 (ここで、"A" の序数値は 0x41 ではありません。) =begin original It is even possible to give your own names to characters, and even to short sequences of characters. For details, see L<charnames>. =end original 文字や、文字の短いシーケンスにあなた自身が名前を与えることも可能です。 詳細は L<charnames> を見てください。 =begin original (There is an expanded internal form that you may see in debug output: C<\N{U+I<wide hex character>.I<wide hex character>...}>. The C<...> means any number of these I<wide hex character>s separated by dots. This represents the sequence formed by the characters. This is an internal form only, subject to change, and you should not try to use it yourself.) =end original (デバッグ出力の中に、拡張された内部形式を見ることがあるかもしれません: C<\N{U+I<wide hex character>.I<wide hex character>...}> 。 この C<...> は、任意の数の I<wide hex character> がドットで区切られたものです。 これは、それらの文字によって構成されているシーケンスを表します。 これは内部形式のみのことであり、将来は変更されるかも知れず、 あなたが使おうとすべきものではありません。) =begin original Mnemonic: I<N>amed character. =end original 覚え方: I<N> は名前がつけられた文字、の頭文字。(I<N>amed character.) =begin original Note that a character that is expressed as a named or numbered character is considered as a character without special meaning by the regex engine, and will match "as is". =end original 名前や、番号による指定で表現された文字は、 正規表現エンジンによって特別な意味を持たない文字として扱われ、 その文字そのものにマッチすることに注意してください。 =head4 Example =begin original use charnames ':full'; # Loads the Unicode names. $str =~ /\N{THAI CHARACTER SO SO}/; # Matches the Thai SO SO character use charnames 'Cyrillic'; # Loads Cyrillic names. $str =~ /\N{ZHE}\N{KA}/; # Match "ZHE" followed by "KA". =end original use charnames ':full'; # Unicode 名をロードする $str =~ /\N{THAI CHARACTER SO SO}/; # タイの SO SO 文字にマッチ use charnames 'Cyrillic'; # キリル文字の名前をロードする $str =~ /\N{ZHE}\N{KA}/; # "ZHE" 文字 "KA" 文字の並びにマッチ =head3 Octal escapes =begin original Octal escapes consist of a backslash followed by two or three octal digits matching the code point of the character you want to use. This allows for 512 characters (C<\00> up to C<\777>) that can be expressed this way (but anything above C<\377> is deprecated). Enough in pre-Unicode days, but most Unicode characters cannot be escaped this way. =end original 8 進エスケープは、バックスラッシュと、 その後ろにあなたが使いたい文字のコードポイントにマッチする 2 文字か 3 文字の 8 進数から成ります。 この方法、512 個の文字 (C<\00> から C<\777> まで) を表現できます。 (しかし、C</377> を超えるものは deprecated です。） =begin original Note that a character that is expressed as an octal escape is considered as a character without special meaning by the regex engine, and will match "as is". 8進エスケープで表現された文字は、 正規表現エンジンによって特別な意味を持たない文字として扱われ、 その文字そのものにマッチすることに注意してください。 =end original =head4 Examples (assuming an ASCII platform) $str = "Perl"; $str =~ /\120/; # Match, "\120" is "P". $str =~ /\120+/; # Match, "\120" is "P", it is repeated at least once. $str =~ /P\053/; # No match, "\053" is "+" and taken literally. =head4 Caveat Octal escapes potentially clash with backreferences. They both consist of a backslash followed by numbers. So Perl has to use heuristics to determine whether it is a backreference or an octal escape. Perl uses the following rules: =over 4 =item 1 If the backslash is followed by a single digit, it's a backreference. =item 2 If the first digit following the backslash is a 0, it's an octal escape. =item 3 If the number following the backslash is N (in decimal), and Perl already has seen N capture groups, Perl will consider this to be a backreference. Otherwise, it will consider it to be an octal escape. Note that if N has more than three digits, Perl only takes the first three for the octal escape; the rest are matched as is. my $pat = "(" x 999; $pat .= "a"; $pat .= ")" x 999; /^($pat)\1000$/; # Matches 'aa'; there are 1000 capture groups. /^$pat\1000$/; # Matches 'a@0'; there are 999 capture groups # and \1000 is seen as \100 (a '@') and a '0'. =back =head3 Hexadecimal escapes Hexadecimal escapes start with C<\x> and are then either followed by a two digit hexadecimal number, or a hexadecimal number of arbitrary length surrounded by curly braces. The hexadecimal number is the code point of the character you want to express. Note that a character that is expressed as a hexadecimal escape is considered as a character without special meaning by the regex engine, and will match "as is". Mnemonic: heI<x>adecimal. =head4 Examples (assuming an ASCII platform) $str = "Perl"; $str =~ /\x50/; # Match, "\x50" is "P". $str =~ /\x50+/; # Match, "\x50" is "P", it is repeated at least once. $str =~ /P\x2B/; # No match, "\x2B" is "+" and taken literally. /\x{2603}\x{2602}/ # Snowman with an umbrella. # The Unicode character 2603 is a snowman, # the Unicode character 2602 is an umbrella. /\x{263B}/ # Black smiling face. /\x{263b}/ # Same, the hex digits A - F are case insensitive. =head2 Modifiers A number of backslash sequences have to do with changing the character, or characters following them. C<\l> will lowercase the character following it, while C<\u> will uppercase (or, more accurately, titlecase) the character following it. (They perform similar functionality as the functions C<lcfirst> and C<ucfirst>). To uppercase or lowercase several characters, one might want to use C<\L> or C<\U>, which will lowercase/uppercase all characters following them, until either the end of the pattern, or the next occurrence of C<\E>, whatever comes first. They perform similar functionality as the functions C<lc> and C<uc> do. C<\Q> is used to escape all characters following, up to the next C<\E> or the end of the pattern. C<\Q> adds a backslash to any character that isn't a letter, digit or underscore. This will ensure that any character between C<\Q> and C<\E> is matched literally, and will not be interpreted by the regexp engine. Mnemonic: I<L>owercase, I<U>ppercase, I<Q>uotemeta, I<E>nd. =head4 Examples $sid = "sid"; $greg = "GrEg"; $miranda = "(Miranda)"; $str =~ /\u$sid/; # Matches 'Sid' $str =~ /\L$greg/; # Matches 'greg' $str =~ /\Q$miranda\E/; # Matches '(Miranda)', as if the pattern # had been written as /\(Miranda\)/ =head2 Character classes Perl regular expressions have a large range of character classes. Some of the character classes are written as a backslash sequence. We will briefly discuss those here; full details of character classes can be found in L<perlrecharclass>. C<\w> is a character class that matches any single I<word> character (letters, digits, underscore). C<\d> is a character class that matches any decimal digit, while the character class C<\s> matches any whitespace character. New in perl 5.10.0 are the classes C<\h> and C<\v> which match horizontal and vertical whitespace characters. The uppercase variants (C<\W>, C<\D>, C<\S>, C<\H>, and C<\V>) are character classes that match any character that isn't a word character, digit, whitespace, horizontal whitespace nor vertical whitespace. Mnemonics: I<w>ord, I<d>igit, I<s>pace, I<h>orizontal, I<v>ertical. =head3 Unicode classes C<\pP> (where C<P> is a single letter) and C<\p{Property}> are used to match a character that matches the given Unicode property; properties include things like "letter", or "thai character". Capitalizing the sequence to C<\PP> and C<\P{Property}> make the sequence match a character that doesn't match the given Unicode property. For more details, see L<perlrecharclass/Backslash sequences> and L<perlunicode/Unicode Character Properties>. Mnemonic: I<p>roperty. =head2 Referencing If capturing parenthesis are used in a regular expression, we can refer to the part of the source string that was matched, and match exactly the same thing. There are three ways of referring to such I<backreference>: absolutely, relatively, and by name. =for later add link to perlrecapture =head3 Absolute referencing A backslash sequence that starts with a backslash and is followed by a number is an absolute reference (but be aware of the caveat mentioned above). If the number is I<N>, it refers to the Nth set of parentheses - whatever has been matched by that set of parenthesis has to be matched by the C<\N> as well. =head4 Examples /(\w+) \1/; # Finds a duplicated word, (e.g. "cat cat"). /(.)(.)\2\1/; # Match a four letter palindrome (e.g. "ABBA"). =head3 Relative referencing New in perl 5.10.0 is a different way of referring to capture buffers: C<\g>. C<\g> takes a number as argument, with the number in curly braces (the braces are optional). If the number (N) does not have a sign, it's a reference to the Nth capture group (so C<\g{2}> is equivalent to C<\2> - except that C<\g> always refers to a capture group and will never be seen as an octal escape). If the number is negative, the reference is relative, referring to the Nth group before the C<\g{-N}>. The big advantage of C<\g{-N}> is that it makes it much easier to write patterns with references that can be interpolated in larger patterns, even if the larger pattern also contains capture groups. Mnemonic: I<g>roup. =head4 Examples /(A) # Buffer 1 ( # Buffer 2 (B) # Buffer 3 \g{-1} # Refers to buffer 3 (B) \g{-3} # Refers to buffer 1 (A) ) /x; # Matches "ABBA". my $qr = qr /(.)(.)\g{-2}\g{-1}/; # Matches 'abab', 'cdcd', etc. /$qr$qr/ # Matches 'ababcdcd'. =head3 Named referencing Also new in perl 5.10.0 is the use of named capture buffers, which can be referred to by name. This is done with C<\g{name}>, which is a backreference to the capture buffer with the name I<name>. To be compatible with .Net regular expressions, C<\g{name}> may also be written as C<\k{name}>, C<< \k<name> >> or C<\k'name'>. Note that C<\g{}> has the potential to be ambiguous, as it could be a named reference, or an absolute or relative reference (if its argument is numeric). However, names are not allowed to start with digits, nor are they allowed to contain a hyphen, so there is no ambiguity. =head4 Examples /(?<word>\w+) \g{word}/ # Finds duplicated word, (e.g. "cat cat") /(?<word>\w+) \k{word}/ # Same. /(?<word>\w+) \k<word>/ # Same. /(?<letter1>.)(?<letter2>.)\g{letter2}\g{letter1}/ # Match a four letter palindrome (e.g. "ABBA") =head2 Assertions Assertions are conditions that have to be true; they don't actually match parts of the substring. There are six assertions that are written as backslash sequences. =over 4 =item \A C<\A> only matches at the beginning of the string. If the C</m> modifier isn't used, then C</\A/> is equivalent with C</^/>. However, if the C</m> modifier is used, then C</^/> matches internal newlines, but the meaning of C</\A/> isn't changed by the C</m> modifier. C<\A> matches at the beginning of the string regardless whether the C</m> modifier is used. =item \z, \Z C<\z> and C<\Z> match at the end of the string. If the C</m> modifier isn't used, then C</\Z/> is equivalent with C</$/>, that is, it matches at the end of the string, or before the newline at the end of the string. If the C</m> modifier is used, then C</$/> matches at internal newlines, but the meaning of C</\Z/> isn't changed by the C</m> modifier. C<\Z> matches at the end of the string (or just before a trailing newline) regardless whether the C</m> modifier is used. C<\z> is just like C<\Z>, except that it will not match before a trailing newline. C<\z> will only match at the end of the string - regardless of the modifiers used, and not before a newline. =item \G C<\G> is usually only used in combination with the C</g> modifier. If the C</g> modifier is used (and the match is done in scalar context), Perl will remember where in the source string the last match ended, and the next time, it will start the match from where it ended the previous time. C<\G> matches the point where the previous match ended, or the beginning of the string if there was no previous match. =for later add link to perlremodifiers Mnemonic: I<G>lobal. =item \b, \B C<\b> matches at any place between a word and a non-word character; C<\B> matches at any place between characters where C<\b> doesn't match. C<\b> and C<\B> assume there's a non-word character before the beginning and after the end of the source string; so C<\b> will match at the beginning (or end) of the source string if the source string begins (or ends) with a word character. Otherwise, C<\B> will match. Mnemonic: I<b>oundary. =back =head4 Examples "cat" =~ /\Acat/; # Match. "cat" =~ /cat\Z/; # Match. "cat\n" =~ /cat\Z/; # Match. "cat\n" =~ /cat\z/; # No match. "cat" =~ /\bcat\b/; # Matches. "cats" =~ /\bcat\b/; # No match. "cat" =~ /\bcat\B/; # No match. "cats" =~ /\bcat\B/; # Match. while ("cat dog" =~ /(\w+)/g) { print $1; # Prints 'catdog' } while ("cat dog" =~ /\G(\w+)/g) { print $1; # Prints 'cat' } =head2 Misc Here we document the backslash sequences that don't fall in one of the categories above. They are: =over 4 =item \C C<\C> always matches a single octet, even if the source string is encoded in UTF-8 format, and the character to be matched is a multi-octet character. C<\C> was introduced in perl 5.6. Mnemonic: oI<C>tet. =item \K This is new in perl 5.10.0. Anything that is matched left of C<\K> is not included in C<$&> - and will not be replaced if the pattern is used in a substitution. This will allow you to write C<s/PAT1 \K PAT2/REPL/x> instead of C<s/(PAT1) PAT2/${1}REPL/x> or C<s/(?<=PAT1) PAT2/REPL/x>. Mnemonic: I<K>eep. =item \N This is a new experimental feature in perl 5.12.0. It matches any character that is not a newline. It is a short-hand for writing C<[^\n]>, and is identical to the C<.> metasymbol, except under the C</s> flag, which changes the meaning of C<.>, but not C<\N>. Note that C<\N{...}> can mean a L<named or numbered character|/Named or numbered characters>. Mnemonic: Complement of I<\n>. =item \R X<\R> C<\R> matches a I<generic newline>, that is, anything that is considered a newline by Unicode. This includes all characters matched by C<\v> (vertical whitespace), and the multi character sequence C<"\x0D\x0A"> (carriage return followed by a line feed, aka the network newline, or the newline used in Windows text files). C<\R> is equivalent to C<< (?>\x0D\x0A)|\v) >>. Since C<\R> can match a sequence of more than one character, it cannot be put inside a bracketed character class; C</[\R]/> is an error; use C<\v> instead. C<\R> was introduced in perl 5.10.0. Mnemonic: none really. C<\R> was picked because PCRE already uses C<\R>, and more importantly because Unicode recommends such a regular expression metacharacter, and suggests C<\R> as the notation. =item \X X<\X> This matches a Unicode I<extended grapheme cluster>. C<\X> matches quite well what normal (non-Unicode-programmer) usage would consider a single character. As an example, consider a G with some sort of diacritic mark, such as an arrow. There is no such single character in Unicode, but one can be composed by using a G followed by a Unicode "COMBINING UPWARDS ARROW BELOW", and would be displayed by Unicode-aware software as if it were a single character. Mnemonic: eI<X>tended Unicode character. =back =head4 Examples "\x{256}" =~ /^\C\C$/; # Match as chr (256) takes 2 octets in UTF-8. $str =~ s/foo\Kbar/baz/g; # Change any 'bar' following a 'foo' to 'baz'. $str =~ s/(.)\K\1//g; # Delete duplicated characters. "\n" =~ /^\R$/; # Match, \n is a generic newline. "\r" =~ /^\R$/; # Match, \r is a generic newline. "\r\n" =~ /^\R$/; # Match, \r\n is a generic newline. "P\x{0307}" =~ /^\X$/ # \X matches a P with a dot above. =begin meta Translated: Atsushi SUGAWARA <peanutsjamjam@gmail.com> =end meta
