php get random file form directory

$dir = //directory
$random_file[1] = "";
$random_file[2] = "";

If there is specific directory, I want to get random file directory as an array.

$dir = "file/infile"

Expected array of $random_file1,2 ==>

$random_file[1] = "file/infile/ran0.jpg";
$random_file[2] = "file/infile/ran1.jpg";