Advanced shell scripting question :-)

[Bob Bell]

On Thu, Sep 05, 2002 at 01:22:20PM -0400, Steven W. Orr <steveo at syslang.net> wrote:
> On Thu, 5 Sep 2002, Bob Bell wrote:
> =>On Thu, Sep 05, 2002 at 10:04:17AM -0400, Steven W. Orr <steveo at syslang.net> wrote:
> =>> What I currently have that gets me closer is as follows:
> =>> 
> =>> p  2>&1 2> >(tee ERR)  | tee BOTH
> =>
> =>    BTW, I don't know what the '2>&1' is for.  I get the same behavior
> =>without it.
> The 2>&1 says "dup stderr onto stdout".

    I'm aware of that.  It just didn't seem necessary (including
empirically) since "tee ERR" will send the output to "tee BOTH".  In
fact, it doesn't seem to have any impact whatsoever (which I'm not sure
I quite understand).

> =>> The problem is this: I expect that when data is written to a pipe, that 
> =>> the the order is preserved. Using this construct, the order is *not* 
> =>> preserved. So on a p that produces many kilobytes of spew, I get big 
> =>> chunks in the BOTH file which are from each seperate channel.
> =>
> =>    I think what you are see is that p is writing to the pipe to "tee
> =>BOTH", and "tee ERR" is writing to the pipe to "tee BOTH".  Due to
> =>scheduling between the two processes, buffering, etc., ordering is not
> =>guaranteed.
> 
> This is actually even closer to what I want. The problem is now strictly 
> that the output into both is not coming out in the same order as what 
> appears on the screen.
> 
> p 2>&1 3> >(tee err 1>&2)  2>&3 | tee both
> 
> So now I have the process substitution tee reading from channel 3 and 
> writing to err and to stderr. (That's the 1>&2)
> 
> Then the 2>&3 says to take stdout and dup it onto channel 3. Finally, the 
> out and error channels are both sent to the final tee where it gets copied 
> to both. It works great, except that the order is not being preserved. :-(
> 
> I was under the impression that the order of was supposed to be preserved 
> because of the pipe mechanism.

    My comments about preserving order stand as written...

-- 
Bob Bell <bobbell at zk3.dec.com>
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