Use of preg regular function in php_PHP tutorial-PHP Tutorial-php.cn

Use of preg regular function in php_PHP tutorial

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Release： 2016-07-13 10:17:19

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Using preg regular function in php

1.The difference between preg_match and preg_match_all
The difference between preg_match and preg_match_all is that preg_match only matches once. And preg_match_all matches everything until the end of the string. Example:

<?php
//注：正则 /a.+?e/ 是非贪婪模式(因为量词‘+’后面加上了‘?’)，如果使用 /a.+?e/U 则变回了贪婪模式
preg_match("/a.+?e/","abcdefgabcdefgabcdefg",$out1);
preg_match_all("/a.+?e/","abcdefgabcdefgabcdefg",$out2);
var_dump($out1);
var_dump($out2);
/*
输出：
array (size=1)
  0 => string &#39;abcde&#39; (length=5)

array (size=1)
  0 =>
    array (size=3)
      0 => string &#39;abcde&#39; (length=5)
      1 => string &#39;abcde&#39; (length=5)
      2 => string &#39;abcde&#39; (length=5)
 */
?>

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2. The difference between greedy mode and non-greedy mode
Such as: String str="abcaxc";
Patter p="ab*c";
Greedy matching: Regular expressions generally tend to match to the maximum length, which is the so-called greedy matching. For example, if the pattern p is used to match the string str, the result is: abcaxc(ab*c).
Non-greedy matching: Just match the result, with fewer matching characters. For example, if the pattern p is used to match the string str, the result is: abc(ab*c).
Example:

<?php
$str = "http://www.baidu/.com?url=www.sina.com/";
preg_match("/http:(.*)com/", $str, $matches1); //贪婪匹配
var_dump($matches1);

preg_match("/http:(.*?)com/", $str, $matches2); //非贪婪匹配(量词&#39;*&#39;后面跟上了&#39;?&#39;)
var_dump($matches2);

/*
array (size=2)
  0 => string &#39;http://www.baidu/.com?url=www.sina.com&#39; (length=38)
  1 => string &#39;//www.baidu/.com?url=www.sina.&#39; (length=30)

array (size=2)
  0 => string &#39;http://www.baidu/.com&#39; (length=21)
  1 => string &#39;//www.baidu/.&#39; (length=13)
 */
?>

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3. The difference between preg_match_all parameters PREG_PATTERN_ORDER (default) and PREG_SET_ORDER

<?php
echo(&#39;PREG_PATTERN_ORDER&#39;);
preg_match_all("|<[^>]+>(.*)</[^>]+>|U",
    "<b>start: </b><b>this is a test</b><b>end</b>",
    $out1);
var_dump($out1);

echo(&#39;PREG_SET_ORDER&#39;);
preg_match_all("|<[^>]+>(.*)</[^>]+>|U",
    "<b>start: </b><b>this is a test</b><b>end</b>",
    $out2, PREG_SET_ORDER);
var_dump($out2);

/*
PREG_PATTERN_ORDER
array (size=2)
  0 =>
    array (size=3)
      0 => string &#39;<b>start: </b>&#39; (length=14)
      1 => string &#39;<b>this is a test</b>&#39; (length=21)
      2 => string &#39;<b>end</b>&#39; (length=10)
  1 =>
    array (size=3)
      0 => string &#39;start: &#39; (length=7)
      1 => string &#39;this is a test&#39; (length=14)
      2 => string &#39;end&#39; (length=3)

PREG_SET_ORDER
array (size=3)
  0 =>
    array (size=2)
      0 => string &#39;<b>start: </b>&#39; (length=14)
      1 => string &#39;start: &#39; (length=7)
  1 =>
    array (size=2)
      0 => string &#39;<b>this is a test</b>&#39; (length=21)
      1 => string &#39;this is a test&#39; (length=14)
  2 =>
    array (size=2)
      0 => string &#39;<b>end</b>&#39; (length=10)
      1 => string &#39;end&#39; (length=3)
 */
?>

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Extended reading: preg_match_all usage examples