Question

我正在查看其他人的旧代码并且无法理解它。

他有：

explode(' ', strtolower(preg_replace('/[^a-z0-9-]+/i', ' ', preg_replace('/\&#?[a-z0-9]{2,4}\;/', ' ', preg_replace('/<[^>]+>/', ' ', $texts)))));

我认为第一个正则表达式排除了a-z和0-9，但我不确定第二个正则表达式的作用。第三个匹配除'< >'

之外的'>'内的任何内容

结果将输出一个包含$texts变量中每个单词的数组，但是，我只是不知道代码是如何产生的。我确实理解preg_replace和其他函数的作用，只是不知道过程是如何工作的

Answer 1

表达式/[^a-z0-9-]+/i将匹配（并随后用空格替换）除 a-z和0-9之外的任何字符。 [^中的^...]表示否定其中包含的字符集。

[^a-z0-9]匹配任何非字母数字字符

+表示前面的一个或多个

/i使其不区分大小写

表达式/\&#?[a-z0-9]{2,4}\;/与&匹配，后跟#，后跟两到四个字母和数字，以;结尾这将match HTML entities like  或'

&#?匹配&或&#，因为?使前面的#成为可选&实际上并不需要转义。< / LI>
[a-z0-9]{2,4}匹配两个和四个字母数字字符

;是字面分号。它实际上并不需要转义。

正如您所怀疑的那样，最后一个会用空格替换<tagname>或<tagname attr='value'>或</tagname>等任何标记。请注意，它与整个标记匹配，而不仅仅是<>的内部内容。

<是文字字符

[^>]+是每个角色，但不包括下一个>

>是文字字符

我真的建议将其重写为对preg_replace()的三次单独调用而不是嵌套它们。

// Strips tags. // Would be better done with strip_tags()!! $texts = preg_replace('/<[^>]+>/', ' ', $texts); // Removes HTML entities $texts = preg_replace('/&#?[a-z0-9]{2,4};/', ' ', $texts); // Removes remainin non-alphanumerics $texts = preg_replace('/[^a-z0-9-]+/i', ' ', $texts); $array = explode(' ', $texts);

Answer 2

此代码看起来像......

剥离HTML / XML标记（＆lt;和＆gt;之间的任何内容）
然后以＆amp;开头的任何事情或＆amp;＃并且长度为2-4个字符（字母数字）
然后剥去任何非字母数字或短划线

处理嵌套的顺序

/<[^>]+>/

Match the character “<” literally «<»
Match any character that is NOT a “>” «[^>]+»
   Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Match the character “>” literally «>»


/\&#?[a-z0-9]{2,4}\;/

Match the character “&” literally «\&»
Match the character “#” literally «#?»
   Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
Match a single character present in the list below «[a-z0-9]{2,4}»
   Between 2 and 4 times, as many times as possible, giving back as needed (greedy) «{2,4}»
   A character in the range between “a” and “z” «a-z»
   A character in the range between “0” and “9” «0-9»
Match the character “;” literally «\;»


/[^a-z0-9-]+/i

Options: case insensitive

Match a single character NOT present in the list below «[^a-z0-9-]+»
   Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
   A character in the range between “a” and “z” «a-z»
   A character in the range between “0” and “9” «0-9»
   The character “-” «-»

PHP正则表达式和preg_replace问题

2 个答案: