Python subprocess module use

Question

How do you specify what directory the python module subprocess uses to execute commands? I want to run a C program and process it's output in Python in near realtime.

I want to excute the command (this runs my makefile for my C program:

make run_pci

In:

/home/ecorbett/hello_world_pthread

I also want to process the output from the C program in Python. I'm new to Python so example code would be greatly appreciated!

Thanks, Edward

Fred Foo · Accepted Answer · 2012-07-10 19:44:01Z

3

Use the cwd argument to Popen, call, check_call or check_output. E.g.

subprocess.check_output(["make", "run_pci"],
                        cwd="/home/ecorbett/hello_world_pthread")

Edit: ok, now I understand what you mean by "near realtime". Try

p = subprocess.Popen(["make", "run_pci"],
                     stdout=subprocess.PIPE,
                     cwd="/home/ecorbett/hello_world_pthread")
for ln in p.stdout:
    # do processing

edited Jul 10, 2012 at 19:44

answered Jul 10, 2012 at 18:38

Fred Foo

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12 Comments

NASA Intern Over a year ago

Thanks! Now how would I capture output from the c program? It simply printfs multiplule lines of text?

Acorn Over a year ago

If you read the documentation you will see that check_output returns the output of the command. docs.python.org/library/subprocess.html#subprocess.check_output

NASA Intern Over a year ago

I see. so doing something like this: process = subprocess.check_output(["make","run_pci"],cwd="/home/ecorbett/hello_world_pthread") print process.communicate() Would be unnecessary/incorrect?

NASA Intern Over a year ago

But back to my original question. If my C program will be running, processing data and producing output that I need to process with my python program simultaneously, will this method still work?

Fred Foo Over a year ago

@NASAIntern: no, then you need to use Popen instead of check_output. Pass it stdout=subprocess.PIPE, then read from its stdout member.

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BrenBarn · Accepted Answer · 2012-07-10 18:39:27Z

0

Read the documentation. You can specify it with the cwd argument, otherwise it uses the current directory of the parent (i.e., the script running the subprocess).

answered Jul 10, 2012 at 18:39

BrenBarn

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