(From man bash)

The test command sorts using ASCII ordering.

-a file
              True if file exists.
-b file
              True if file exists and is a block special file.
-c file
              True if file exists and is a character special file.
-d file
              True if file exists and is a directory.
-e file
              True if file exists.
-f file
              True if file exists and is a regular file.
-g file
              True if file exists and is set-group-id.
-h file
              True if file exists and is a symbolic link.
-k file
              True if file exists and its ``sticky'' bit is set.
-p file
              True if file exists and is a named pipe (FIFO).
-r file
              True if file exists and is readable.
-s file
              True if file exists and has a size greater than zero.
-t fd
              True if file descriptor fd is open and refers to a terminal.
-u file
              True if file exists and its set-user-id bit is set.
-w file
              True if file exists and is writable.
-x file
              True if file exists and is executable.
-G file
              True if file exists and is owned by the effective group id.
-L file
              True if file exists and is a symbolic link.
-N file
              True if file exists and has been modified since it was last read.
-O file
              True if file exists and is owned by the effective user id.
-S file
              True if file exists and is a socket.
file1 -ef file2
              True if file1 and file2 refer to the same device and inode numbers.
file1 -nt file2
              True if file1 is newer (according to modification date) than file2, or if file1 exists and file2 does not.
file1 -ot file2
              True if file1 is older than file2, or if file2 exists and file1 does not.