How to use a variable to indicate a file descriptor in bash?

Question

I want to use a bash variable to indicate a file descriptor, like this:

id=6
file=a
exec $id<>$file

But the usage is wrong:

-bash: exec: 6: not found

So, how to use a variable to indicate a file descriptor in exec command?

Answer 1

You have to use eval and put the entire expression in quotes.

eval "exec $id<>$file"

And do that every time you want to use $id.