redirection in linux

 2>&1
      # Redirects stderr to stdout.
      # Error messages get sent to same place as standard output.
        >>filename 2>&1
            bad_command >>filename 2>&1
            # Appends both stdout and stderr to the file "filename" ...
        2>&1 | [command(s)]
            bad_command 2>&1 | awk '{print $5}'   # found
            # Sends stderr through a pipe.
            # |& was added to Bash 4 as an abbreviation for 2>&1 |.

   i>&j
      # Redirects file descriptor i to j.
      # All output of file pointed to by i gets sent to file pointed to by j.

   >&j
      # Redirects, by default, file descriptor 1 (stdout) to j.
      # All stdout gets sent to file pointed to by j.