In-depth analysis of sub-patterns of regular expressions
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。下面我们就来详细了解下子模式
首先,我们先看一段PHP代码:
<?php $time = date ("Y-m-d H:i:s"); $pattern = "/\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}/i"; if(preg_match($pattern,$time,$arr)){ echo "<pre class="brush:php;toolbar:false">"; print_r($arr); echo ""; } ?>
显示结果:
Array ( [0] => 2012-06-23 03:08:45 )
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:
<?php $time = date ("Y-m-d H:i:s"); $pattern = "/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/i"; if(preg_match($pattern,$time,$arr)){ echo "<pre class="brush:php;toolbar:false">"; print_r($arr); echo ""; } ?>
注意:我只修改了$pattern,在匹配模式中,使用了括号()
执行结果:
Array ( [0] => 2012-06-23 03:19:23 [1] => 2012 [2] => 06 [3] => 23 [4] => 03 [5] => 19 [6] => 23 )
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。
对整个正则匹配模式进行了分组以后,就可以进一步使用“向后引用”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
我们可以进一步修改下代码,如下所示:
<?php $time = date ("Y-m-d H:i:s"); $pattern = "/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/i"; $replacement = "\$time格式为:$0<BR>替换后的格式为:\\1年\\2月\\3日 \\4时\\5分\\6秒"; print preg_replace($pattern, $replacement, $time); if(preg_match($pattern,$time,$arr)){ echo "<pre class="brush:php;toolbar:false">"; print_r($arr); echo ""; } ?>
注意:
因为是在双引号中,所以使用分组的时候应该使用两个反斜杠,如:\\1,而如果在单引号中,则使用一个反斜杠就可以了,如:\1
\\1用于捕获分组一种的内容:2012,\\6用于捕获分组6中的内容
执行结果:
$time格式为:2012-06-23 03:30:31 替换后的格式为:2012年06月23日 03时30分31秒 Array ( [0] => 2012-06-23 03:30:31 [1] => 2012 [2] => 06 [3] => 23 [4] => 03 [5] => 30 [6] => 31 )
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