正規表達式 Regular Expression

Metacharacters

用來描敘match項目的特殊字元，可組合使用

符號	說明
.	任一字元
ˆ	放在最前面表示後面的符號需在開頭，如果在中間表是否定
$	符號需在結尾字串
\s	Match any whitespace character
\d	Match any digit
\w	Match any “word” character

Quantifiers
指定次數

符號	說明
*	The character can appear zero or more times
+	The character can appear one or more times
?	The character can appear zero or one times
()	表示一個 sub pattern ，符合 sub pattern 的字串內容會被存放在匹配陣列中，並依序指派數字代表此 sub pattern 。 例如 /The h([0-9]) means Title (\1)/ 即為 'The h1 means Title 1', 'The h2 means Title 2' ...
[]	表示字串含有括號中任一字元的內容。可以 - 表示一組連續字元，例如 /[a-z]/, /[0-9]/ 。注意， [] 僅代表一個字元，例如 /[abc]/ 表示 'a' 或 'b' 或 'c' ，而不是 'abc' /ab[cd]e/ abce, abde皆正確 /ab[c-e\d]/  abc, abd, abe及任何ab後接數字皆正確
{n,m}	The character can appear at least n times, and no more than m. Either parameter can be omitted to indicated a minimum limit with no maximum, or a maximumlimit without a minimum, but not both.

Example

驗證

`[a-zA-Z0-9]$` 英數字，不含特殊字元

取值

• 取html tag值或attribute
  

  //取tag value
  function getTextBetweenTags($string, $tagname) {
      $pattern = "/<$tagname ?.*>(.*)<\/$tagname>/";
      preg_match($pattern, $string, $matches);
      return $matches[1];
  }
  
  //取tag attribue
  function getAttribute($attrib, $tag){
                  //get attribute from html tag
                  $re = '/' . preg_quote($attrib) . '=([\'"])?((?(1).+?|[^\s>]+))(?(1)\1)/is';
                  if (preg_match($re, $tag, $match)) {
                          return urldecode($match[2]);
                  }
                  return false;
          }
  

• host相關
  

  // get host name from URL
  preg_match('@^(?:http://)?([^/]+)@i',
      "http://www.php.net/index.html", $matches);
  $host = $matches[1];
  
  // get last two segments of host name
  preg_match('/[^.]+\.[^.]+$/', $host, $matches);
  echo "domain name is: {$matches[0]}\n";



• 取代
  將轉換tag - php

  $subjects['body'] = "[b]Make Me Bold![/b]";
  $subjects['subject'] = "[i]Make Me Italics![/i]";
  $regex[] = "@\[b\](.*?)\[/b\]@i";
  $regex[] = "@\[i\](.*?)\[/i\]@i";
  $replacements[] = "<b>$1</b>";
  $replacements[] = "<i>$1</i>";
  $results = preg_replace($regex, $replacements, $subjects);
  
  //ouput---
  array(2) {
    ["body"]=>
      string(20) "<b>Make Me Bold!</b>"
    ["subject"]=>
      string(23) "<i>Make Me Italic!</i>"
  }




• 驗證 

References Regular Expression (RegExp) in JavaScript