On Fri, Jun 09, 2006 at 03:38:58PM -0400, Bernard Lebel wrote: > Hi, > > I'd like to know what are the differences at the various os.popenX > flavors. I read the documentation and I can see they return file > objects..... so what can you do with these file objects? I mean, why > would you need a set of file objects rather than another? >
See documentation at http://docs.python.org/lib/os-newstreams.html#l2h-1552. And, notice how the return values from the various versions of popen are different file types: stdin, stdout, and stderr. A summary: - popen() gives you either an input pipe (stdin) or an output pipe (stdout) but not both. - popen2() gives you both an input pipe (stdin) and output pipe (stdout). - popen3() gives you an input pipe (stdin) and output pipe (stdout) and an error pipe (stderr). - popen4() gives you an input pipe and a pipe that combines output and errors (stdout and stderr). Specifically, if you want to run a command, just like you would with os.system(), but: 1. You want to *either* feed (pipe) text to your command *or* read results from your command, use os.popen() and use mode= 'w' or 'r'. 2. You want to both feed (pipe) text to your command *and* read results from your command, use os.popen2(). Etc. If you get an input pipe, you should write text to that pipe, then close that stream. Doing close() is what triggers execution of the command. If you get an output pipe, then (after the command runs), read from that pipe to get the results of your command (i.e. the text that the command wrote to stdout). Here is a simple example that uses popen2:: import os def test(): instream, outstream = os.popen2('grep dave') instream.write('Line #1\n') instream.write('Line #2 dave is here\n') instream.write('Line #3\n') instream.write('Line #4 dave is also here\n') instream.write('Line #5\n') instream.close() for line in outstream: print 'Line: %s' % line.rstrip() test() Note that there is also a popen module, which has functions with the same names and functionality: "This functionality is also available in the popen2 module using functions of the same names, but the return values of those functions have a different order." See: http://docs.python.org/lib/module-popen2.html Hope this helps. Dave -- Dave Kuhlman http://www.rexx.com/~dkuhlman _______________________________________________ Tutor maillist - [email protected] http://mail.python.org/mailman/listinfo/tutor
