Korn Shell file options (condition check)

           -r file              file exists and is readable.
           -w file              file exists and is writable.
           -x file              file   exists  and  is  exe­
                                cutable.
           -a file              file exists.
           -e file              file exists.
           -f file              file is a regular file.
           -d file              file is a directory.
           -c file              file is a character  special
                                device.
           -b file              file   is  a  block  special
                                device.
           -p file              file is a named pipe.
           -u file              file's mode has  setuid  bit
                                set.
           -g file              file's  mode  has setgid bit
                                set.
           -k file              file's mode has  sticky  bit
                                set.
           -s file              file is not empty.
           -O file              file's  owner is the shell's
                                effective user-ID.
           -G file              file's group is the  shell's
                                effective group-ID.
           -h file              file is a symbolic link.
           -H file              file  is a context dependent
                                directory  (only  useful  on
                                HP-UX).
           -L file              file is a symbolic link.
           -S file              file is a socket.

           file -nt file        first  file  is  newer  than
                                second file  or  first  file
                                exists  and  the second file
                                does not.
           file -ot file        first  file  is  older  than
                                second  file  or second file
                                exists and  the  first  file
                                does not.
           file -ef file        first  file is the same file

From: man ksh on SUSE Linux.