[Discuss] bash output buffering

[John Abreau]

On Wed, Jun 13, 2012 at 7:06 AM, Edward Ned Harvey <blu at nedharvey.com> wrote:

> A command inside of bash generates output every second (ping) redirected to
> a file.
> If you run the command on an interactive shell, then you can tail -f the
> file, and see the output "live" as it happens.
> But if you run the command inside an "at" script, or a cron script, you tail
> -f the file...  And nothing appears for a few minutes, and then it all
> appears suddenly.
>
> This is bash buffering the output of ping, before redirecting to file.  All
> of which is a level above the OS filesystem buffering.

What you're describing is the difference between OS tty buffering vs
OS filesystem buffering. This has nothing at all to do with bash; both
occur below bash at the OS level.

The difference is that OS filesystem buffering is block-oriented, and
OS tty buffering is character-oriented.


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John Abreau / Executive Director, Boston Linux & Unix
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