Basic application of PHP regular expressions

The code is as follows:

<?php 
//正则表达 式 
// ereg区分大小写 
if(ereg("([A-Z]{3,})", "AAA")){ 
echo "大写能匹配！<br>"; 
}else{ 
echo "no"; 
} 
if(ereg("([A-Z]{3,})", "aaa")){ 
echo "yes"; 
}else{ 
echo "小写不能匹配！<br>"; 
} 
// eregi不区分大小写 
if(eregi("([A-Z]{3,})","Aaaa")){ 
echo "大小写都可以匹配!"; 
} 
//返回匹配的值 
if(ereg("^(0[0-9]{2,3})-([0-9]{7,8})","0592-5337138",$regs)){ 
echo "返回值0下标为原串$regs[0]<br>"; 
echo "返回区号（即第一个匹配串）".$regs[1]."<br>"; 
echo("返回电话号码(即第二个匹配串)$regs[2]<br>"); 
} 
?>