Fwd: read -t 0 fails to detect input.

[Bize Ma]

To: Chester Ramey <chet.ramey@case.edu>

On thu., dec. 19 of 2019 at 12:40, Chet Ramey (<chet.ramey@case.edu>) wrote:

> On 12/18/19 6:40 PM, Bize Ma wrote:
>


> >>> The exit status is 0 if input is available on the specified file
> >   descriptor, non-zero otherwise.
>
> Bash-5.0 uses select/FIONREAD to determine whether or not there is input
> available on the file descriptor. Those don't wait; they test whether or
> not there is input on the specified file descriptor at the point they are
> called.
>

Thanks Chet.

Could you please comment about this assertions:

 1.-   bash will either do a select() or an ioctl(FIONREAD), or neither of
them, but not both, as it should for it to work. read -t0 is broken. Do not
use it – mosvy.
<https://unix.stackexchange.com/questions/33049/how-to-check-if-a-pipe-is-empty-and-run-a-command-on-the-data-if-it-isnt/498064#comment969997_498064>
 2.- Conclusion: read -t0 is *broken* in bash. Don't use it. –
<https://unix.stackexchange.com/users/308316/mosvy> mosvy
<https://unix.stackexchange.com/questions/33049/how-to-check-if-a-pipe-is-empty-and-run-a-command-on-the-data-if-it-isnt/498065?noredirect=1#comment916652_497121>