Results from os.system() different from execution at prompt

[Enno Middelberg]

Hi all,

I am using mpeg_encode under Linux to generate little movies. The
parameter file is generated by a Python script, the last line of which is

os.system('mpeg_encode mpeg.par')

When I execute the same command at the bash prompt, the resulting movie
is longer, i.e., it has more frames.

I have piped the outpout from both the Python-executed and
prompt-executed mpeg_encode into files and found a difference, although
the parameter files were the same file in both runs:

Prompt-executed:

MPEG ENCODER STATS (1.5b)
------------------------
TIME STARTED: Mon Dec 29 16:33:08 2003
MACHINE: PC227
FIRST FILE: /homes/emiddelb/local/pics/eberg_movie/webcam/title.jpg
LAST FILE: /homes/emiddelb/local/pics/eberg_movie/webcam/eff_1975
PATTERN: ibbbpbbbpbbb
GOP_SIZE: 30
SLICES PER FRAME: 1
(...)

Python's os.system():

MPEG ENCODER STATS (1.5b)
------------------------
TIME STARTED: Mon Dec 29 16:28:05 2003
MACHINE: PC227
FIRST FILE: /homes/emiddelb/local/pics/eberg_movie/webcam/title.jpg
LAST FILE: /homes/emiddelb/local/pics/eberg_movie/webcam/eff_1
PATTERN: ibbbpbbbpbbb ^^^^^^^^^^^^
GOP_SIZE: 30
SLICES PER FRAME: 1
(...)
So, the Python-executed mpeg_encode reports fewer input files. Any clues
why this could happen? Is there a limit on the command length or so? I
see no reason why the results from the two ways of calling mpeg_encode
should be different.
Kind regards,

Enno

[Mathias Waack]

Enno Middelberg wrote:

So, the Python-executed mpeg_encode reports fewer input files. Any
clues why this could happen? Is there a limit on the command length
or so?

Why do you think the reason for this behaviour could be truncated
command line? You just call 'mpeg_encode mpeg.par', this line
shouldn't be too long neither for python nor for the shell.

Mathias

[Jeff Epler]

On Mon, Dec 29, 2003 at 05:38:25PM +0100, Mathias Waack wrote:

Enno Middelberg wrote:

So, the Python-executed mpeg_encode reports fewer input files. Any
clues why this could happen? Is there a limit on the command length
or so?

Why do you think the reason for this behaviour could be truncated
command line? You just call 'mpeg_encode mpeg.par', this line
shouldn't be too long neither for python nor for the shell.

.... and a commandline that is too long should cause a non-zero return
status, not run the program with an incorrect argument list:

os.system("true x") 0 os.system("true " + "x" * 320000)

32512