Capture output from C program on stdout using Python subprocess? Pexpect?

Question

I want to capture output from a C program I\'m launching like this:

p = subprocess.Popen([\"make\", \"run_pci\"],
                     stdout=subprocess.PIPE         


        

Answer 1

The reason you need to use pexpect is that the program's stdio will use block buffering if it is not connected to a tty. pexpect uses a pseudo-tty (pty) so stdio will use line buffering and you will be able to access lines as they are output.

Change your code to:

p = pexpect.spawn('make', ['run_pci'], cwd="/home/ecorbett/hello_world_pthread")
for ln in p:
    ...

You can use pexpect.spawn.expect to just get the output you're interested in:

while p.expect('Thread on Tile (\d+):', pexpect.EOF) == 0:
    print("Tile {0}".format(int(p.group[1])))