Detailed explanation of the usage of php regular modifiers

RegularCommonly used pattern modifiers in expressions include i, g, m, s, x, e, etc. They can be used in combination.
Their functions are as follows:
//Modifier: i case-insensitive matching;
//Modifier: g represents global matching
//Modifier: m will characters The string is treated as multiple lines, and it can be matched no matter which line it is;
//Modifier: s treats the string as a single line, and the newline character is treated as an ordinary character;
//Modifier: x treats the pattern Blank spaces in are ignored;
//Modifier:A forces matching from the beginning of the target string;
//Modifier:D If $ is used to limit the ending character, no newline at the end is allowed;
// Modifier: U only matches the most recent string; does not match repeatedly;

<?php
   //标记在整个模式之外;
   // 例://$mode="/\bis\b/U",其中U在外面;
  //修正符:i 不区分大小写的匹配;
     //如:"/abc/i"可以与abc或aBC或ABc等匹配;
  //修正符:m 将字符串视为多行,不管是那行都能匹配;
  //  例://模式为:$mode="/abc/m";
     //要匹配的字符串为:$str="bcefg5e\nabcdfe"
     //注意其中\n,换行了;abc换到了下一行;
     //$str和$mode仍可以匹配,修正符m使得多行也可匹配;
  //修正符:s 将字符串视为单行,换行符作为普通字符;
   // 例://模式为:$mode="/pr.y/";
      //要匹配字符串为:$str="pr\ny";
      //两者不可匹配; . 是除了换行以外的字符可匹配;
      //修改下模式为:$mode="/pr.y/s";
        //其中修正符s将\n视为普通字符,即不是换行;
      //最后两者可以匹配;
  //修正符:x 将模式中的空白忽略;
  //修正符:A 强制从目标字符串开头匹配;
   // 例://$mode="/abc/A";
      //可以与$str="abcsdfi"匹配,
      //不可以与$str2="sdsdabc"匹配;
      //因为$str2不是以abc开头;
  //修正符:D 如果使用$限制结尾字符,则不允许结尾有换行;
  //  例://模式为:$mode="/abc$/";
      //可以与最后有换行的$str="adshabc\n"匹配;
      //元子符$会忽略最后的换行\n;
      //如果模式为:$mode="/abc/D",
      //则不能与$str="adshabc\n"匹配,
      //修正符D限制其不可有换行;必需以abc结尾;
  //修正符:U 只匹配最近的一个字符串;不重复匹配;
  //  例:
  //   如模式为:
      $mode="/a.*c/";
      $str="abcabbbcabbbbbc" ;
      preg_match($mode,$str,$content);
      echo $content[0]; //输出:abcabbbcabbbbbc;
      //如果$mode="/a.*c/";变成$mode="/a.*c/U";
      // 则只匹配最近一个字符串,输出:abc;
//修正符:e 配合函数preg_replace()使用,
//      可以把匹配来的字符串当作正则表达式执行;
?>

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