转自https://www.cnblogs.com/sgm4231/p/9782271.html
php中常用的正则表达式函数 
* preg_match() 
* preg_match_all() 
* preg_replace() 
* preg_filter() 
* preg_grep() 
* preg_split() 
* preg_quote()

接下来对比讲解：

讲解中 $pattern 通常表示正则表达式 
      $subject 通常表示目标处理数据 
定义一个方法 方便查看数据类型：

function show($val = null){
    if(empty($val)){        
    //打印空
        echo 'null';
    }elseif(is_array($val) || is_object($val)){        
    //打印数组或者对象
        echo '<pre>';
        print_r($val);        
        echo '</pre>';
    }else{        
    //打印string int float
        echo $val;
    }
}

preg_match()与preg_match_all()

  preg_match($pattern,$subject,[array &$matches])  //匹配一次  第三个参数可选  匹配结果放置matches数组
  preg_match_all($pattern,$subject,array &matches) //匹配多次  三参必选      匹配结果放置matches数组

  $pattern = '/[0-9]/';
  $subject='b5fg4sgf3sd2f1g';
  $m1 =preg_match($pattern,$subject,$arr1);

show($m1);
show($arr1);
/*
 1
Array
(
    [0] => 5
)
 */

$m2 =preg_match_all($pattern,$subject,$arr2);

show($m2);
show($arr2);

/*
 5
Array
(
    [0] => Array
        (
            [0] => 5
            [1] => 4
            [2] => 3
            [3] => 2
            [4] => 1
        )
)
 */

2.preg_replace()与preg_filter()
/*方法简单说明*/
 * preg_replace与preg_filter
 * preg_replace($pattern,$replacement,$subject)
 * //正则替换函数被替换对象是数组 返回全部
   //正则替换函数 被替换对象是数组 仅返回被替换元素
 * 联想：str_repalce() 
 * echo str_replace("world","Shanghai","Hello world!");
 * //得到Hello Shanghai!

//第一测 字符串中替换字符串 结论：此处preg_replace()与preg_filter()无区别
$pattern = '/[0-9]/';
$subject='b65fg4sgf3sd2f1g';
$replacement = '_';
$str1 = preg_replace($pattern,$replacement,$subject);
$str2 = preg_filter($pattern,$replacement,$subject);
echo '<hr>';
show($str1);
echo '<br>';
show($str2);
/*
b__fg_sgf_sd_f_g
b__fg_sgf_sd_f_g
 */

 //第二测  字符串中根据数组正则 替换  结论：此处preg_replace()与preg_filter()无区别
 $pattern = array('/[123]/','/[456]/','/[789]/');
 $subject='b123fg3456sgf3789f1g';
 $replacement = array('天','地','人');
 $str3 = preg_replace($pattern,$replacement,$subject);
 $str4 = preg_filter($pattern,$replacement,$subject);
 echo '<hr>';
show($str3);
echo '<br>';
show($str4);
/*
b天天天fg天地地地sgf天人人人f天g
b天天天fg天地地地sgf天人人人f天g
 */

 //第三测  数组中根据数组正则 替换  结论：此处展示preg_repalce()与preg_filter()有区别
 $pattern = array('/[123]/','/[456]/','/[789]/');
 $subject=array('b','fg3','456','sgf','789','fg');
 $replacement = array('天','地','人');
 $str5 = preg_replace($pattern,$replacement,$subject);
 $str6 = preg_filter($pattern,$replacement,$subject);
 echo '<hr>';
show($str5);
echo '<br>';
show($str6);
/*
Array
(
    [0] => b
    [1] => fg天
    [2] => 地地地
    [3] => sgf
    [4] => 人人人
    [5] => fg
)

Array
(
    [1] => fg天
    [2] => 地地地
    [4] => 人人人
)
 */
3 . preg_grep($pattern, array $subject) //此处$subject只可以为一维数组

/*函数说明*/
preg_grep($pattern,array $input)//只可以匹配一维数组 返回匹配成功的数组元素
可以理解preg_grep()为阉割版 preg_filter()
只做了匹配 不作替换

$pattern = '/[0-9]/';
$subject=array('b','fg3','456','sgf','789','fg');
$arr = preg_grep($pattern,$subject);
show($arr);
/*
Array
(
    [1] => fg3
    [2] => 456
    [4] => 789
)
 */

4 . preg_split($pattern,$subject)//一匹配成功为切割点切割字符串成数组 
可以理解preg_split()升级版的explode()

$pattern = '/[0-9]/';
$subject='bfg3456sgf789fg';
$arr = preg_split($pattern,$subject);
show($arr);
/*
Array
(
    [0] => bfg
    [1] =>
    [2] =>
    [3] =>
    [4] => sgf
    [5] =>
    [6] =>
    [7] => fg
)
 */
5 . preg_quote($str) 正则运算符转译
/*
 * preg_quote($str) 正则运算符转译
 *  . \ + * ? [ ^ ] $ () {} = ! < > | : -
 *
 */
 echo '<hr>';
 $str = "qewr{asdf}[123]";
 $str =preg_quote($str);
print_r($str);
/*
qewr\{asdf\}\[123\]
*/
简单总结通性： 
preg_ 开头 
除preg_quote函数以外，第一个参数都是正则表达式 
preg_match 表单验证等 
preg_replace 非法词语过滤等