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 ?
Redirect stdout to 6 and stderr to stdout (so it will be further redirected to 6):
command >&6 2>&1
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
&>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.