execl difficulty

Fredrik Lundh fredrik at pythonware.com
Mon Dec 15 00:18:32 CET 2003

"python newbie" wrote:

> Can anyone tell me why this would cause "Invalid Number of Parameters" while
> trying to compile (or interpret or whatever)
> import os
> os.execl("C:/WINDOWS/system32/xcopy.exe","E:/MainWeb/dreampics/*.*","E:/Main
> Web/dp")
> Here's what the Python reference says:
>      execl(path,arg0, arg1, ...)

first, fix the slashes.  xcopy wants backward slashes in the filenames,
not forward slashes.

next, fix the number of arguments.  at the top of the reference page
you refer to, there's a paragraph explaining how the exec arguments

    The various exec*() functions take a list of arguments for the
    new program loaded into the process. In each case, the first
    of these arguments is passed to the new program as its own
    name rather than as an argument a user may have typed on
    a command line. For the C programmer, this is the argv[0]
    passed to a program's main(). For example, "os.execv('/bin/echo',
    ['foo', 'bar'])" will only print "bar" on standard output;
    "foo" will seem to be ignored.

    (from http://www.python.org/doc/current/lib/os-process.html )

in other words, you need to pass in the program name twice, to make
sure xcopy sees the filenames as argument 1 and 2.

(are you sure you want os.exec, btw?  os.system or os.spawn* might
be a better choice...)


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