On Mon, Aug 27, 2012 at 3:52 AM, Ray Jones <crawlz...@gmail.com> wrote: > > Yes, the Bash call worked (in fact I tried it just prior to sending the > original message just to be sure). > > I guess I'm a bit confused about 'splitting' the arguments. You said > that Python splits arguments on spaces. What exactly happens to the > arguments if we split them up into individual strings separated by commas?
I meant that only in comparison to how the shell tokenizes a command. For example, in the shell if you want spaces to be ignored, you have to escape them or use quotes, and if you want to include raw quotes/backslashes you have to escape them too. To tokenize a command string as the shell would, you can use shlex.split(): http://docs.python.org/library/shlex.html#shlex.split Otherwise the space character doesn't have any special significance. What matters is that all of the argument strings are in the list in the right order. It doesn't matter how they get there. So instead of using shlex.split you may as well build the list directly. Popen uses the args list/tuple to call the executable (after forking and setting up the pipes). This passes through the os module on to the built-in posix module. There it eventually calls the POSIX system function execv(path, argv). (FYI, in Windows there's no fork/exec; Win32 CreateProcess is used instead.) POSIX is a system standard that's part of the core UNIX standard (unix.org). It's a collaboration between IEEE and The Open Group. Here's the documentation for the exec family of calls: http://pubs.opengroup.org/onlinepubs/009604499/functions/exec.html Here's their description of the arguments of execv(path, argv): * The argument "path" points to a pathname that identifies the new process image file. * The argument "argv" is an array of character pointers to null- terminated strings. The application shall ensure that the last member of this array is a null pointer. These strings shall constitute the argument list available to the new process image. The value in argv[0] should point to a filename that is associated with the process being started by one of the exec functions. Most programs expect their arguments to have been tokenized as the shell would as a matter of convention. So, for example, if vlc gets "-I" in argv[1] it expects that argv[2] will be a value such as "dummy". A value of "-I dummy" in argv[1] in principle shouldn't work. In practice vlc seems pretty flexible and accepts it both ways. _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
