php从文件夹随机读取文件的方法

//用法演示：
// "jpg|png|gif" matches all files with these extensions
print RandomFile('test_images/','jpg|png|gif');
// returns test_07.gif
// "." matches all extensions (all files)
print RandomFile('test_files/','.');
// returns foobar_1.zip
// "[0-9]+" matches all extensions that just
// contain numbers (like backup.1,backup.2)
print RandomFile('test_files/','[0-9]+');
// returns backup.7