有关 2&>1,man bash

       Bash  allows both the standard output (file descriptor 1) and the stan-

       dard error output (file descriptor 2) to  be  redirected  to  the  file

       whose name is the expansion of word with this construct.

       There  are  two  formats  for  redirecting standard output and standard

       error:

              &>word

       and

              >&word

       Of the two forms, the first is preferred.  This is semantically equiva-

       lent to

              >word 2>&1