If the file handle came from a piped open `close'
   will additionally return false if one of the other
   system calls involved fails or if the program exits
   with non-zero status.  (If the only problem was that
   the program exited non-zero `$!' will be set to
   `0'.)  Closing a pipe also waits for the process
   executing on the pipe to complete, in case you want
   to look at the output of the pipe afterwards, and
   implicitly puts the exit status value of that
   command into `$?'.

   ...

   close OUTPUT                # wait for sort to finish
       or warn $! ? "Error closing sort pipe: $!"
                  : "Exit status $? from sort";