how can I silence all of the output from a particular python command?

Question

Autodesk Maya 2012 provides "mayapy" - a modded build of python filled with the necessary packages to load Maya files and act as a headless 3D editor for batch work. I'm calling it from a bash script. If that script opens a scene file in it with cmds.file(filepath, open=True) , it spews pages of warnings, errors, and other info I don't want. I want to turn all of that off only while the cmds.file command is running.

I've tried redirecting from inside of the Python commands I'm sending into mayapy inside the shell script, but that doesn't work. I can silence everything by redirecting stdout/err to /dev/null in the call to the bash script. Is there any way to silence it in the call to the shell, but still allow my passed-in command inside the script to print out information?

test.sh:

#!/bin/bash

/usr/autodesk/maya/bin/mayapy -c "
cmds.file('filepath', open=True);
print 'hello'
"

calling it:

$ ./test.sh                  # spews info, then prints 'hello'
$ ./test.sh > /dev/null 2>&1 # completely silent

Answer 1

Basically, I think the best way to solve this is to implement a wrapper that will execute test.sh and sanitize the output to the shell. To sanitize the output, I would simply prepend some string to notify your wrapper that this text is good for output. My inspiration for the wrapper file came from this: https://stackoverflow.com/a/4760274/2030274

The contents are as follows:

import subprocess

def runProcess(exe):
    p = subprocess.Popen(exe, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
    while(True):
      retcode = p.poll() #returns None while subprocess is running
      line = p.stdout.readline()
      yield line
      if(retcode is not None):
        break

for line in runProcess(['./test.sh']):
  if line.startswith('GARYFIXLER:'):
      print line,

Now you could imagine test.sh being something along the lines of

#!/bin/bash

/usr/autodesk/maya/bin/mayapy -c "
cmds.file('filepath', open=True);
print 'GARYFIXLER:hello'
"

and this will only print the hello line. Since we are wrapping the python call in a subprocess, all output typically displayed to the shell should get captured and you should intercept the lines that you don't want.

Of course, to call test.sh from a python script, you need to make sure you have the correct permissions.

Answer 2

I knew I was just getting twisted around with pipes. Maya is indeed sending all batch output to stderror. This frees stdout entirely once you properly pipe stderr away. Here's an all-bash one-liner that works.

# load file in batch; divert Maya's output to /dev/null
# then print listing of things in file with cmds.ls()
/usr/autodesk/maya/bin/mayapy -c "import maya.standalone;maya.standalone.initialize(name='python');cmds.file('mayafile.ma', open=True);print cmds.ls()" 2>/dev/null