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Date: Fri, 2 Dec 2011 13:50:29 -0500
Message-ID: <CAG_2cTm+VQcNuRmDTFEheEyuOAeWA4tCW5+whH74E6D4UkAFAg@mail.gmail.com>
Subject: Re: Redirecting output from running proc doesn't modify the "last modified time" field for target file
From: Jon Clugston <jon.clugston@gmail.com>
To: cygwin@cygwin.com
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On Fri, Dec 2, 2011 at 1:42 PM, ajshower <ajshower@gmail.com> wrote:
>
>>IMHO, this is a very dubious "feature" to depend upon.  If you want to
>>know if the file has changed, why not check its length instead?
>
> I have switched to using the length instead but I was interested in what
> people thought of the issue.
>
> I'm having trouble reproducing this using just Cygwin so I'm not presenting
> the problem accurately.  My process is to call  Runtime.getRuntime.exec()
> within a java process which opens cygwin/bin/bash.exe and then runs the
> redirection command from within the bash.  From the same java process that
> called exec(), I'm trying to monitor the last modified time based on what's
> going on in the previously called bash.exe.  That does sound pretty
> convoluted.  I guess it's some kind of scope problem, but checking length()
> is working, so it's all moot anyway.
>

I reproduced your symptoms with this simple shell script:

while sleep 10 ; do
  echo
done >x.log &

While this loop is running, the timestamp on "x.log" doesn't change
(whereas on Linux it changes every 10 seconds).  It sure looks to me
that Windows just doesn't bother updating the file timestamp while it
is open.  I don't know if this update is required by POSIX - I would
doubt that it is.


Jon

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