opendir DIR,$dir or die "Can't open directory.\n";
@dir = readdir DIR;
...
foreach(@dir) {
    if (-d$_) {print $_," is a directory.\n";}
    elsif (-f$_) {print $_," is a file.\n";}
    else {print $_," is not a file or a directory!\n";}
    
}
[download]

readdir() gives you directory entries without the path component. So you have to either chdir() into the directory before your foreach loop, or write

foreach(@dir) {
    my $path = "$dir/$_";  # prepend dir
    if (-d $path) {print $path," is a directory.\n";}
    elsif (-f $path) {print $path," is a file.\n";}
    else {print $path," is not a file or a directory!\n";}
}
[download]