Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions

Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions_PHP tutorial

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Release： 2016-07-12 08:54:05

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正则表达式的子模式详解，正则表达式详解

首先，我们先看一段PHP代码：

Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions_PHP tutorial

<?<span>php
    </span><span>$time</span> = <span>date</span> ("Y-m-d H:i:s"<span>);
    </span><span>$pattern</span> = "/\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}/i"<span>; 
    </span><span>if</span>(<span>preg_match</span>(<span>$pattern</span>,<span>$time</span>,<span>$arr</span><span>)){
    </span><span>echo</span> "<pre class="brush:php;toolbar:false">"<span>;
    </span><span>print_r</span>(<span>$arr</span><span>);        
    </span><span>echo</span> "

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"; } ?> Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions_PHP tutorial

显示结果：

<span>Array
(
    [0] => 2012-06-23 03:08:45
)</span>

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有没有注意到，显示的结果只有一条数据，即符合匹配模式的时间格式，那如果只有一条记录的话，为什么还要用数组保存呢？直接使用字符串保存不是更好？

带着这个问题，我们来看下正则表达式中的子模式。

在正则表达式中，可以使用“(”和“)”将模式中的子字符串括起来，以形成一个子模式。将子模式视为一个整体时，那么它就相当于一个单个字符。

比如，我们将以上的代码稍微修改下，改成如下：

<?<span>php
    </span><span>$time</span> = <span>date</span> ("Y-m-d H:i:s"<span>);
    </span><span>$pattern</span> = "/<span>(</span>\d{4}<span><strong>)</strong></span>-<span>(</span>\d{2}<span>)</span>-<span>(</span>\d{2}<span>)</span> <span>(</span>\d{2}<span>)</span>:<span>(</span>\d{2}<span>)</span>:<span>(</span>\d{2}<span>)</span>/i"<span>; 
    </span><span>if</span>(<span>preg_match</span>(<span>$pattern</span>,<span>$time</span>,<span>$arr</span><span>)){
    </span><span>echo</span> "<pre class="brush:php;toolbar:false">"<span>;
    </span><span>print_r</span>(<span>$arr</span><span>);        
    </span><span>echo</span> "

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"; } ?> Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions_PHP tutorial

注意：我只修改了$pattern，在匹配模式中，使用了括号()

执行结果：

<span>Array</span><span>
(
    [</span>0] => 2012-06-23 03:19:23<span>
    [</span>1] => 2012<span>
    [</span>2] => 06<span>
    [</span>3] => 23<span>
    [</span>4] => 03<span>
    [</span>5] => 19<span>
    [</span>6] => 23<span>
)</span>

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总结：我们可以使用小括号给整个匹配模式进行分组，默认情况下，每个分组会自动拥有一个组号，规则是，从左到右，以分组的左括号为标志，第一个出现的分组为组号1，第二个为组号2，以此类推。其中，分组0对应整个正则表达式。<br />对整个正则匹配模式进行了分组以后，就可以进一步使用&ldquo;向后引用&rdquo;来重复搜索前面的某个分组匹配的文本。例如：\1代表分组1匹配的文本，\2代表分组2匹配的文本等等<br />我们可以进一步修改下代码，如下所示：

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<?<span>php
    </span><span>$time</span> = <span>date</span> ("Y-m-d H:i:s"<span>);
    </span><span>$pattern</span> = "/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/i"<span>;
    </span><span>$replacement</span> = "\$time格式为：$0<BR>替换后的格式为：\\1年\\2月\\3日 \\4时\\5分\\6秒"<span>;
    </span><span>print</span> <span>preg_replace</span>(<span>$pattern</span>, <span>$replacement</span>, <span>$time</span><span>);
    </span><span>if</span>(<span>preg_match</span>(<span>$pattern</span>,<span>$time</span>,<span>$arr</span><span>)){
        </span><span>echo</span> "<pre class="brush:php;toolbar:false">"<span>;
        </span><span>print_r</span>(<span>$arr</span><span>);        
        </span><span>echo</span> "

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"; } ?> Detailed explanation of sub-patterns of regular expressions, detailed explanation of regular expressions_PHP tutorial

注意：

执行结果：

<span>$time格式为</span>：2012-06-23 03:30:31<span>
替换后的格式为：2012年06月23日 03时30分31秒
</span><span>Array</span><span>
(
    [</span>0] => 2012-06-23 03:30:31<span>
    [</span>1] => 2012<span>
    [</span>2] => 06<span>
    [</span>3] => 23<span>
    [</span>4] => 03<span>
    [</span>5] => 30<span>
    [</span>6] => 31<span>
)</span>

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<br /><br />

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