Depending on what you're doing, you may want lstat rather than stat. lstat does not follow symlinks, but instead gives information on the link itself.

The upper bits aren't as magic as they may seem - they tell the file type. From man 2 stat:

The following flags are defined for the st_mode field:

S_IFMT     0170000   bitmask for the file type bitfields
S_IFSOCK   0140000   socket
S_IFLNK    0120000   symbolic link
S_IFREG    0100000   regular file
S_IFBLK    0060000   block device
S_IFDIR    0040000   directory
S_IFCHR    0020000   character device
S_IFIFO    0010000   fifo
S_ISUID    0004000   set UID bit
S_ISGID    0002000   set GID bit (see below)
S_ISVTX    0001000   sticky bit (see below)
S_IRWXU      00700   mask for file owner permissions
S_IRUSR      00400   owner has read permission
S_IWUSR      00200   owner has write permission
S_IXUSR      00100   owner has execute permission
S_IRWXG      00070   mask for group permissions
S_IRGRP      00040   group has read permission
S_IWGRP      00020   group has write permission
S_IXGRP      00010   group has execute permission
S_IRWXO      00007   mask for permissions for others (not in group)
S_IROTH      00004   others have read permission
S_IWOTH      00002   others have write permisson
S_IXOTH      00001   others have execute permission

The set GID bit (S_ISGID) has several special uses: For a directory
it indicates that BSD semantics is to be used for that directory:
files created there inherit their group ID from the directory, not
from the effective gid of the creating process, and directories
created there will also get the S_ISGID bit set. For a file that
does not have the group execution bit (S_IXGRP) set, it indicates
mandatory file/record locking.

The `sticky' bit (S_ISVTX) on a directory means that a file in that
directory can be renamed or deleted only by the owner of the file,
by the owner of the directory, and by root.

To make those constants portable and available by name in perl, use Fcntl ':mode';