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Re: bash sets O_NONBLOCK on pts


From: Matteo Croce
Subject: Re: bash sets O_NONBLOCK on pts
Date: Wed, 2 Oct 2019 19:59:24 +0200

On Wed, Oct 2, 2019 at 7:50 PM Andrew Church <address@hidden> wrote:
>
> >Well, it's not so uncommon, I had it a few times. Reading on internet
> >it seems that other users have it but don't notice it.
>
> The fault could be in some other program accessing the terminal.  Bash
> does not clear O_NONBLOCK on displaying a prompt, so if a previously
> executed program sets O_NONBLOCK on stdin and then exits, that state
> will remain until some other program unsets it.  For example:
>
> $ cat >foo.c
> #include <fcntl.h>
> int main(void) {fcntl(0, F_SETFL, O_NONBLOCK); return 0;}
> ^D
> $ cc foo.c
> $ ./a.out
> $ cat
> cat: -: Resource temporarily unavailable
>
>   --Andrew Church
>     http://achurch.org/

It seems to me that bash restores the flag, cat prints an error when not:

$ cat
$

the same is not true if running multiple commands:

$ ./foo; cat
cat: -: Resource temporarily unavailable
$

Why this different behaviour?

Regards,

--
Matteo Croce
per aspera ad upstream




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