[BUG] failure to push/restore closed file descriptor

[Martijn Dekker]

$ bash -c '{ exec 8</dev/null; } 8<&-; : <&8 && echo "oops, still open"'
Output: "oops, still open"
Expected output: Bad file descriptor

Apparently, bash either fails to push the file descriptor onto the stack 
at '} 8<&-', or fails to restore it.

Same bug with loops ending in "done 8<&-".

Confirmed in all bash versions down to 2.05b.

Also note that pushing an open file descriptor works as expected:

$ bash -c '{ exec 8</dev/null; } 8</dev/tty; : <&8 && echo "oops, still 
open"'
Output: Bad file descriptor (as expected)

FYI:
* bash and dash have this bug;
* zsh, yash, AT&T ksh93, pdksh, mksh, posh, schily's bosh, Busybox ash, 
FreeBSD sh, and NetBSD sh all do this correctly.

Thanks,

- Martijn