Detailed explanation of php basic functions

<?php
//生成随机数 和 时间函数
//echo rand();
//echo "<br>";
//echo rand(0,10);
//echo time();//时间戳
//2017-02-10 08:46:12
date_default_timezone_set("Asia/Shanghai");
//echo date("Y-m-d h:i:s");//默认转换当前时间
//echo date("Y-m-d h:i:s",&#39;1386688343&#39;);
//echo strtotime("2013-12-10 11:12:23");
//字符串的处理
$str = &#39;Hello World!!!&#39;;
//echo strlen($str);
//$str1=&#39;Abc&#39;;
//$str2=&#39;abc&#39;;
//echo strcmp($str1,$str2);
//echo strcasecmp($str1,$str2);
echo strtoupper($str2);
echo strtolower($str1);
//$str = "a|B|c|d";
//$str1 = explode("|",$str);
//echo implode("&",$str1);
//echo substr($str,1,3);
//echo str_replace("|","&",$str);
//echo substr_replace($str,"%",1,1);
$str = "hello3 world4 ashdf223sdfa2323sd45454";
//preg_match("/\d/",$str,$str2);
//preg_match_all("/\d/",$str,$str3);
//var_dump($str3);
//$str4 = preg_replace("/\d/", "数字", $str);
//var_dump($str4);
$str5 = preg_split("/\d/",$str);
var_dump($str5);