Re: [9fans] on cp /fd/1 /fd/0

[Daniel Bastos <dbastos@toledo.com>]

On Tue, May 12, 2015 at 1:15 PM, Charles Forsyth
<charles.forsyth@gmail.com> wrote:
> On 12 May 2015 at 15:17, Daniel Bastos <dbastos@toledo.com> wrote:
>>
>> What is the relationship between file descriptor 1 and /fd/1? When a
>> program runs, 1 is already open for writing. But apparently it's open only
>> for writing. A read on it yields inappropriate use of fd. The same seems to
>> happen /fd/1. Can I say they'll both always present the same behavior?
>
> open /fd/1 and you get a new file descriptor number that refers to the same
> open file as file descriptor 1, and with the same open mode
> (the new open can add OCEXEC, which will apply to both). /fd/1ctl  shows
> what you get.

I don't follow you. The only way I could open successfully was to
specify OWRITE (with or without OCEXEC). The results were expected:
with OCEXEC, the fd was closed after an exec, without it it was kept
open. I don't know what you wanted to show me.

My conclusion is that

  cp /fd/1 anything

could never work because it requires opening /fd/1 for reading, which
is not possible. Is this conclusion incorrect?