How to know if a system command doesn't exist?

[John J. Lee]

Nicolas Fleury <nid_oizo at yahoo.com_remove_the_> writes:
> Nicolas Fleury wrote:
[...]
> >     How can I know if a system command doesn't exist?  All the ways
> > I have tried behave like if the system command was existing but
> > returning one.  I don't want to sound provocative, but open in Perl
[...]

Haven't tried popen(), but I assume C's system() (of which os.system()
is a trivial wrapper, on posix-y OSes) is implemented in terms of
popen() (or both are implemented in terms of similar lower-level
stuff).  I get different return codes from system() depending on
whether the program exists or not, as expected:

>>> os.system("nonsense")
sh: nonsense: command not found
32512
>>> os.system("ls")
[...snip directory listing...]
0
>>> os.system("ls nonsense")
ls: nonsense: No such file or directory
256
>>>


John