PHP determines character type php reads matching condition string from file

Case description:

Find all characters in the text file (input.txt) that meet the following conditions

1. It is a lowercase letter, and

2. There are only three uppercase letters on each side (consider newlines) ) For example, b in xAAAbAAAd

First create input.txt

in the same level directory, and then type some English letters in the file (can be regular or irregular)

For example:

asadfsaxAAAbAAAdRYTaASD

Create a php file

The code is as follows:

<?php 
header(&#39;content-type:text/html;charset=utf8 &#39;);

function getLower($data){
    $length = strlen($data)-1;
    $str = &#39;&#39;;
    for ($i=0;$i<$length;$i++){
        $flag = true;
        if(!isUpper($data[$i])){//当前为小写 成立
            if($i == 3){
                $flag = getFlag($data,$i);
                //如果后第四个是大写 不成立
                if(isUpper($data[$i+4])){
                    $flag = false;
                }
            }else if($i == $length-3){
                $flag = getFlag($data,$i);
                //如果前第四个是大写 不成立
                if(isUpper($data[$i-4])){
                    $flag = false;
                }
            }else if($i>3 && $i<$length-3){
                $flag = getFlag($data,$i);
                //如果前||后第四个有一个是大写就不成立
                if(isUpper($data[$i+4]) || isUpper($data[$i-4])){
                    $flag = false;
                }
            }else{
                $flag = false;
            }
            if($flag){
                @$str .= $data[$i];
            }
        }
    }
    return $str;
}
//公共当前字符的前三后和三个
function getFlag($data,$i){
    $flag = true;
    for($j=$i-3;$j<=$i+3;$j++){
        if($j != $i){
           //如果有一个是小写就不成立
           if(!isUpper($data[$j])){
              $flag = false;
           }
        }
    }
    return $flag;
}
/* 判断是否是大写字母*/
 
function isUpper($s){
    if(@ord($s) < 97){
        return true;
    }else{
        return false;
    }
}
$res ='';
$d=file_get_contents('input.txt');
$res = getlower(str_replace("\r\n","",$d));
echo $res;

The effect is as follows (browser output):

bda

The above introduces PHP to determine the character type. PHP reads the matching condition string from the file, including the content of PHP to determine the character type. I hope it will be helpful to friends who are interested in PHP tutorials.