Detailed explanation of regular expression application in php

$str = "2hello 5li 6lei";
echo preg_replace("/\d/","#",$str);

$str = "2hello 5li 6lei";
var_dump(preg_split("/\d/",$str));

$str = "2hello 5li 6lei";
preg_match_all("/\d",$str,$arr);     //正则表达式，定义的字符串，数组
var_dump($arr);                            //匹配满足所有正则的字符串

$str = "2hello 5li 6lei";
preg_match("/\d/",$str,$arr);
var_dump($arr);

生成随机数
echo rand();
echo "<br>";
echo rand(0,10);
echo "<br>";
//获取当前时间
echo time();
echo "<br>";
//格式化显示时间
echo date("Y-m-d H:i:s","1506494423");
echo "<br>";
echo strtotime("2017-09-27 14:40:23");

字符串函数
去字符串长度
$str1="as";
$str2="abcdecdcd";
//比较长度ASC代码
var_dump(strcmp($str2,$str1));
//显示长度
echo strlen($str);