Redirect stderr and stdout to another file descriptor

Question

exec 6>&1 will copy file descriptor 1 onto 6.

But how can I copy both stderr and stdout (1 and 2)to file descriptor 6 ?

Answer 1

Redirect stdout to 6 and stderr to stdout (so it will be further redirected to 6):

command >&6 2>&1

Answer 2

I don't think you can redirect two files descriptors in one, but you can use two files descriptors pointing to one file

exec 1>./all.txt
exec 2>./all.txt

Answer 3

Try with:

command &>&6

---

&>filename  
    # Redirect both stdout and stderr to file "filename."  
    # This operator is now functional, as of Bash 4, final release.  
M>&N  
    # "M" is a file descriptor, which defaults to 1, if not set.  
    # "N" is another file descriptor.