Read stdout from shell command, was: Becoming root

[Donn Cave]

Quoth wware-nospam at world.std.com (Will Ware):
...
| The thing I'd really like to know is how to do the Python
| equivalent of a shell command of this form:
|
| variable = `some shell command`
|
| where "some shell command" prints to standard output.
| I find I do this quite frequently, usually using something like
| os.popen('some shell command').readline()[:-1] and sure, it works,
| but it's really ugly, and I'm always left with the nagging suspicion
| that since I didn't explicitly close the os.popen(), it might still
| be floating around.

Empirically, the pipe file descriptor does close when the object goes
out of scope, from what I see with other file descriptor unit numbers
allocated subsequently by pipe() or open().

I rolled my own pipe/fork/exec system a ways back and use it a lot,
and you're welcome to it -
ftp://ftp.u.washington.edu/pub/user-supported/donn/cmdproc.py

I use it mostly the way you describe, to store the output of a
command in a variable.  The long way to spell it is

 variable = cmdproc.RaiseCommand('/bin/sh',
		('sh', '-c', 'some shell command')).expand()

(Actually I often invoke the command directly rather than through the
shell, but the above example serves to illustrate both.)

The RaiseCommand class also raises an exception when the command exits
with an error, with the exception value set to the diagnostic (unit 2)
output.  I think that's the feature that really sets this apart from
just another way to spell popen().

	Donn Cave, University Computing Services, University of Washington
	donn at u.washington.edu