How do I automatically redirect stdout and stderr when using os.popen2?

[Grant Edwards]

On 2006-06-07, mikem76 at gmail.com <mikem76 at gmail.com> wrote:

> How do I automatically redirect stdout and stderr when using os.popen2
> to start a long running process.

popen2 does redirect stdout to a file object.  That's the whole
point of using it.  If you don't want a file object that's
connected to the child's stdout, then don't use popen2.

> If the process prints a lot of stuff to stdout it will
> eventually stop because it runs out of buffer space. Once I
> start reading the stdout file returned by os.popen2 then the
> process resumes.  I know that I could just specify > /dev/null
> when starting the process but I'd like to know if there is a
> way to start a process using os.popen2 or some other way so
> that all standard out and standard error goes to /dev/null or
> some other file.

Yes.  Fork a child process then use the standard file
descriptor operators to open /dev/null or some other file and
then dup those file descriptors to stdout/stderr:

  http://docs.python.org/lib/os-fd-ops.html

Then you can exec the program you want to run:

  http://docs.python.org/lib/os-process.html

This is basically identical to the method use to do I/O
redirection in C, so any decent book on C programming under
Unix should have a good explanation.


Hmmm, it looks like it's simpler touse the subprocess module.
Just open /dev/null to get a file descriptor for it, and then
pass that to subprocess.Popen():

  http://docs.python.org/lib/module-subprocess.html

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