Why dup()?

[David Newall]

On 13/10/17 18:40, Clark Wang wrote:
> On Fri, Oct 13, 2017 at 3:24 PM, David Newall <openssh at davidnewall.com 
> <mailto:openssh at davidnewall.com>> wrote:
>
>
>        ssh localhost 'exec cat > /dev/null' | { read l; echo ${l:-EOF}; }
>
>     One should see "EOF" immediately (for values of immediate that
>     include startup latency), but that's not what happens.
>
>
> The ssh is still alive since the remote cat is waiting for input so 
> the read would not see EOF. Did you actually mean 'exec cat < /dev/null'?
>

The ssh is still alive since the remote cat is waiting for input. That 
has zero relevance to EOF.  If you still don't get it, please replace 
"ssh localhost" with "sh -c" and see what should happen.