getimagesize（真实格式，支持base64）

代码：

<?php
/*
@desc：获取图片真实后缀
@param   name    文件名
@return  suffix  文件后缀
*/   
function getimgsuffix($name) {
$info = getimagesize($name);
$suffix = false;
if($mime = $info['mime']){
    $suffix = explode('/',$mime)[1];
}
return $suffix;
}

测试：

$suffix = getimgsuffix('http://192.168.8.81/public/image/01.jpg');
echo $suffix;

输出：

jpeg

二进制方法（真实格式）

代码：

<?php
/*
@desc：获取文件真实后缀
@param   name    文件名
@return  suffix  文件后缀
*/   
function getfilesuffix($name) {
$file = fopen($name, "rb");
$bin = fread($file, 2); // 只读2字节
fclose($file);
$info = @unpack("C2chars", $bin);
$code = intval($info['chars1'] . $info['chars2']);
$suffix = "unknow";
if($code == 255216){
    $suffix = "jpg";
}elseif($code == 7173){
    $suffix = "gif";
}elseif($code == 13780){
    $suffix = "png";
}elseif($code == 6677){
    $suffix = "bmp";
}elseif($code == 7798){
    $suffix = "exe";
}elseif($code == 7784){
    $suffix = "midi";
}elseif($code == 8297){
    $suffix = "rar";
}elseif($code == 7368){
    $suffix = "mp3";
}elseif($code == 0){
    $suffix = "mp4";
}elseif($code == 8273){
    $suffix = "wav";
}
return $suffix;
}

测试：

$suffix = getfilesuffix('http://192.168.8.81/public/image/01.jpg');
echo $suffix;

输出：

jpg

strrchr strrpos substr

<?php
    $filename = "phpddt.jpg";
    echo substr(strrchr($filename,"."),1);
?>

或

<?php
    $filename = "phpddt.jpg";
    echo substr($filename,strrpos($filename,".")+1);
?>

explode array_pop

<?php
    $filename = "phpddt.jpg";
    $arr = explode(".",$filename);
    echo array_pop($arr);
?>

pathinfo

<?php
    $filename = "phpddt.jpg";
    $info = pathinfo($filename);
    echo $info['extension'];
?>

或

<?php
    $filename = "phpddt.jpg";
    echo pathinfo($filename,PATHINFO_EXTENSION);
?>