The docs for subprocess.Popen are missing at least one piece of information that is crucial to using it for portable code. That is, on POSIX systems, the PATH environment variable is always used to look up directory-less executable names, but on Windows, PATH is only considered when shell=True. Please see http://bugs.python.org/issue8557 -- Dave Abrahams Meet me at BoostCon: http://www.boostcon.com BoostPro Computing http://www.boostpro.com