problem using [FILTER} to run a bash script

progress_re = re.compile("^FILTER_PROGRESS=(\\d*)$")
def filter_program(program_filter, infilename, outfilename):
    import subprocess
    outfile = open(outfilename, "w")
    infilename_q = infilename.replace("'", "'\\''")
    env = dict(os.environ)
    env['AXIS_PROGRESS_BAR'] = '1'
    p = subprocess.Popen(["sh", "-c", "%s '%s'" % (program_filter, infilename_q)],
                          stdin=subprocess.PIPE,
                          stdout=outfile,
                          stderr=subprocess.PIPE,
                          env=env)
    p.stdin.close()  # No input for you
    progress = Progress(1, 100)
    progress.set_text(_("Filtering..."))
    stderr_text = []
    try:
        while p.poll() is None: # XXX add checking for abort
            t.update()
            r,w,x = select.select([p.stderr], [], [], 0.100)
            if r:
                stderr_line = p.stderr.readline()
                m = progress_re.match(stderr_line)
                if m:
                    progress.update(int(m.group(1)), 1)
                else:
                    stderr_text.append(stderr_line)
                    sys.stderr.write(stderr_line)
        # .. might be something left on stderr
        for line in p.stderr:
            m = progress_re.match(line)
            if not m:
                stderr_text.append(line)
                sys.stderr.write(line)
        return p.returncode, "".join(stderr_text)
    finally:
        progress.done()

def get_filter(filename):
    ext = os.path.splitext(filename)[1]
    if ext:
        return inifile.find("FILTER", ext[1:])
    else:
        return None