blog/content/post/2008/02/25/2008-02-25-『新版perl言語プログラミング...

---
title: 『新版Perl言語プログラミングレッスン入門編』第8章
author: kazu634
date: 2008-02-25
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categories:
  - Perl
  - Programming

---
<div class="section">
<p>
    　「もっと正規表現」というセクション名だよー
</p>

<p>
<a name="seemore"></a>
</p>

<h4>
    簡単なマッチ
</h4>

<p>
    　「=~」という演算子を用いて色々とごにゃごにゃする。
</p>

<pre class="syntax-highlight">
<span class="synIdentifier">$str</span> =~<span class="synStatement"> /</span><span class="synSpecial">\d+</span><span class="synStatement">/</span>
</pre>

<p>
    とすると、数字列が存在すればTrueを、存在しなければFalseを返す。
</p>

<h4>
    マッチした範囲を取り出したい！
</h4>

<p>
    　特殊な変数「$&」を用いると、マッチした範囲を取り出すことができる。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;The price is 300yen.&#34;</span>;
<span class="synStatement">if</span> (<span class="synIdentifier">$str</span> =~<span class="synStatement"> /</span><span class="synSpecial">\d+</span><span class="synStatement">/</span>) {
<span class="synStatement">print</span> <span class="synConstant">&#34;</span><span class="synIdentifier">$&#38;</span><span class="synConstant"> is the number</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
}
</pre>

<p>
    この場合は、「$&」には「300」が入る。
</p>

<h4>
    マッチした範囲を複数取り出す！
</h4>

<p>
    　特殊変数「$&」はマッチした部分を取り出すのに役に立ちます。こいつを使うのはマッチさせたい箇所が一つだけのとき。もし文字列の中でマッチさせたい部分が複数ある時は$1, $2, $3, &#8230;, $nを用います。$1, $2, $3, &#8230;には正規表現の中で()に囲まれた部分が自動的に設定されます。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;168, 57, 37&#34;</span>;
<span class="synStatement">if</span> (<span class="synIdentifier">$str</span> =~<span class="synStatement"> /</span><span class="synSpecial">(\d+)</span><span class="synConstant">, </span><span class="synSpecial">(\d+)</span><span class="synConstant">, </span><span class="synSpecial">(\d+)</span><span class="synStatement">/</span>) {
<span class="synStatement">my</span> <span class="synIdentifier">$height</span> = <span class="synIdentifier">$1</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$weight</span> = <span class="synIdentifier">$2</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$age</span> = <span class="synIdentifier">$3</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Height: </span><span class="synIdentifier">$height</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Weight: </span><span class="synIdentifier">$weight</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Age: </span><span class="synIdentifier">$age</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
}
</pre>

<p>
    こいつの別な書き方としては
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;168, 57, 37&#34;</span>;
<span class="synStatement">if</span> (<span class="synIdentifier">$str</span> =~<span class="synStatement"> /</span><span class="synSpecial">(\d+)</span><span class="synConstant">, </span><span class="synSpecial">(\d+)</span><span class="synConstant">, </span><span class="synSpecial">(\d+)</span><span class="synStatement">/</span>) {
<span class="synStatement">my</span> (<span class="synIdentifier">$height</span>, <span class="synIdentifier">$weight</span>, <span class="synIdentifier">$age</span>) = (<span class="synIdentifier">$1</span>, <span class="synIdentifier">$2</span>, <span class="synIdentifier">$3</span>);
<span class="synStatement">print</span> <span class="synConstant">&#34;Height: </span><span class="synIdentifier">$height</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Weight: </span><span class="synIdentifier">$weight</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Age: </span><span class="synIdentifier">$age</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
}
</pre>

<p>
    上の二つのプログラムは「コンマで区切られた数字列を取り出す」という見方で作られている。仮に（数字列に限らず）「コンマで区切られた文字列を取り出す」という視点に立てば次のようになる。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;168, 57, 37&#34;</span>;
<span class="synStatement">my</span> (<span class="synIdentifier">$height</span>, <span class="synIdentifier">$weight</span>, <span class="synIdentifier">$age</span>) = <span class="synStatement">split</span>(<span class="synStatement">/</span><span class="synConstant">,</span><span class="synStatement">/</span>, <span class="synIdentifier">$str</span>);
<span class="synStatement">print</span> <span class="synConstant">&#34;Height: </span><span class="synIdentifier">$height</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Weight: </span><span class="synIdentifier">$weight</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;Age: </span><span class="synIdentifier">$age</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
</pre>

<p>
    ちなみに複数マッチするように正規表現をくんだとき、「$& = $1」である。また「$1, $2, $3, &#8230;, $n」は左括弧の順で代入されていく。
</p>

<h4>
    \1という表記
</h4>

<p>
    　\1は正規表現の中で用いて、直前の正規表現と同じものを指します。例えば「/[bcdfghjklmnpqrstvwxyz]([aeiou])\1」と表記することで、
</p>

<ul>
<li>
      see
</li>
<li>
      too
</li>
</ul>

<p>
    などにマッチする。「()」は必須。
</p>

<h4>
    変数$_とパターンマッチ
</h4>

<p>
    　単に「/^From:/」と書くと、デフォルト変数の$_がパターンマッチの対象になる。
</p>

<h4>
    簡単な置換
</h4>

<p>
    　基本は
</p>

<pre class="syntax-highlight">
<span class="synStatement">s/</span><span class="synConstant">置換前</span><span class="synStatement">/</span><span class="synConstant">置換後</span><span class="synStatement">/</span>
</pre>

<p>
    という形。例としては
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;How I wonder what you are.</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">s/</span><span class="synConstant">what</span><span class="synStatement">/</span><span class="synConstant">who</span><span class="synStatement">/</span>;
<span class="synStatement">print</span> <span class="synIdentifier">$str</span>;
</pre>

<p>
    こいつはマッチするのが複数あっても、最初の一つだけしか置換しない。全部置換させたい場合は「s/置換前/置換後/g」と表記する。
</p>

<h4>
    特殊変数$&を置換で使う
</h4>

<p>
    　言うまでもなく「$&」はマッチした部分を指す。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;How I wonder what you are.</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">s/</span><span class="synConstant">what</span><span class="synStatement">/</span><span class="synSpecial">\*</span><span class="synIdentifier">$&#38;</span><span class="synSpecial">\*</span><span class="synStatement">/</span>;
<span class="synStatement">print</span> <span class="synIdentifier">$str</span>;
</pre>

<p>
    こいつだと、マッチした部分を「*」で囲んでいる。
</p>

<h4>
    マッチした部分の削除
</h4>

<p>
    　「s/置換前//」と表記する。
</p>

<h4>
    特殊変数$1, $2, $3, &#8230;の利用
</h4>

<p>
    　マッチの時と同じように、()でくくったパターンにマッチした文字列を左括弧の順に$1, $2, $3, &#8230; という特殊変数で得ることができます。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;The price is 300yen. The distance is 120km.</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">s/</span><span class="synSpecial">((\d+)([A-Za-z]+))</span><span class="synStatement">/</span><span class="synIdentifier">$2</span><span class="synConstant">&#60;</span><span class="synIdentifier">$3</span><span class="synConstant">&#62;</span><span class="synStatement">/g</span>;
<span class="synStatement">print</span> <span class="synIdentifier">$str</span>;
</pre>

<h4>
    式を評価する修飾子 /e
</h4>

<p>
    　修飾子「/e」をつけると、置換後の部分をPerlの式として評価（計算）してくれます。
</p>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;How I wonder what you are.</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">s/</span><span class="synSpecial">\w+</span><span class="synStatement">/</span><span class="synConstant">ucfirst(</span><span class="synIdentifier">$&#38;</span><span class="synConstant">)</span><span class="synStatement">/eg</span>;
<span class="synStatement">print</span> <span class="synIdentifier">$str</span>;
</pre>

<h4>
    メタ文字 \b
</h4>

<p>
    　正規表現でメタ文字 \b は、単語の境界にマッチするものです。
</p>

<h4>
    tr///による置換の例
</h4>

<pre class="syntax-highlight">
<span class="synStatement">use strict</span>;
<span class="synStatement">use warnings</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">&#34;How I wonder what you are.</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">tr/</span><span class="synConstant">A-Za-z</span><span class="synStatement">/</span><span class="synConstant">a-zA-Z</span><span class="synStatement">/</span>;
<span class="synStatement">print</span> <span class="synIdentifier">$str</span>;
</pre>

<h4>
    tr///の使い方
</h4>

<p>
    　ここで使われている「tr///」は、次のような形式で用い、文字を置換したり削除したりするのに用いられます。使用例は
</p>

<pre class="syntax-highlight">
<span class="synStatement">tr/</span><span class="synConstant">置換元の文字リスト</span><span class="synStatement">/</span><span class="synConstant">置換先の文字リスト</span><span class="synStatement">/</span>オプション
</pre>

<p>
    という感じ。tr///の戻り値は置換（あるいは削除）した文字数になります。
</p>

<h4>
    tr///の慣用句(1): 英大文字の数を数える
</h4>

<pre class="syntax-highlight">
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">'This is Perl.'</span>;
<span class="synStatement">my</span> <span class="synIdentifier">$count</span> = (<span class="synIdentifier">$str</span> =~ <span class="synStatement">tr/</span><span class="synConstant">A-Z</span><span class="synStatement">/</span><span class="synConstant">A-Z</span><span class="synStatement">/</span>);
<span class="synStatement">print</span> <span class="synIdentifier">$count</span>, <span class="synConstant">&#34;</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
</pre>

<h4>
    tr///の慣用句(2): $nameを$unameに代入し、$unameの方だけをすべて大文字にする
</h4>

<pre class="syntax-highlight">
<span class="synStatement">my</span> <span class="synIdentifier">$name</span> = <span class="synConstant">'Hiroshi'</span>;
(<span class="synStatement">my</span> <span class="synIdentifier">$uname</span> = <span class="synIdentifier">$name</span>) =~ <span class="synStatement">tr/</span><span class="synConstant">a-z</span><span class="synStatement">/</span><span class="synConstant">A-Z</span><span class="synStatement">/</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;</span><span class="synSpecial">\$</span><span class="synConstant">name = </span><span class="synIdentifier">$name</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;</span><span class="synSpecial">\$</span><span class="synConstant">uname = </span><span class="synIdentifier">$uname</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
</pre>

<h4>
    tr///の慣用句(3): 英小文字を削除する
</h4>

<pre class="syntax-highlight">
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">'Yahoo!JAPAN &#38; Yahoo! (USA)'</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">tr/</span><span class="synConstant">a-z</span><span class="synStatement">//d</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;|</span><span class="synIdentifier">$str</span><span class="synConstant">|</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
</pre>

<h4>
    tr///の慣用句(4): 英数字以外を1個のスペースに置換する
</h4>

<pre class="syntax-highlight">
<span class="synStatement">my</span> <span class="synIdentifier">$str</span> = <span class="synConstant">'Yahoo!JAPAN &#38; Yahoo! (USA)'</span>;
<span class="synIdentifier">$str</span> =~ <span class="synStatement">tr/</span><span class="synConstant">A-Za-z0-9</span><span class="synStatement">/</span><span class="synConstant"> </span><span class="synStatement">/cs</span>;
<span class="synStatement">print</span> <span class="synConstant">&#34;|</span><span class="synIdentifier">$str</span><span class="synConstant">|</span><span class="synSpecial">\n</span><span class="synConstant">&#34;</span>;
</pre>
</div>