My problem is this--I need to get output from a subprocess and I am using the following code to call it-- (Feel free to ignore the long arguments. The importing thing is the stdout= subprocess.PIPE)
(stdout, stderr) = subprocess.Popen([self.ChapterToolPath, "-x", book.xmlPath , "-a", book.aacPath , "-o", book.outputPath+ "/" + fileName + ".m4b"], stdout= subprocess.PIPE).communicate()
print stdout
Thanks to an answer below, I've been able to get the output of the program, but I still end up waiting for the process to terminate before I get anything. The interesting thing is that in my debugger, there is all sorts of text flying by in the console and it is all ignored. But the moment that anything is written to the console in black (I am using pycharm) the program continues without a problem. Could the main program be waiting for some kind of output in order to move on? This would make sense because I am trying to communicate with it.... Is there a difference between text that I can see in the console and actual text that makes it to the stdout? And how would I collect the text written to the console?
Thanks!
The first line of the documentation for subprocess.call() describes it as such:
Run the command described by args. Wait for command to complete, then return the returncode attribute.
Thus, it necessarily waits for the subprocess to exit.
subprocess.Popen(), by contrast, does not do this, returning a handle on a process with which one than then communicate().
To get all output from a program:
from subprocess import check_output as qx
output = qx([program, arg1, arg2, ...])
To get output while the program is running:
from subprocess import Popen, PIPE
p = Popen([program, arg1, ...], stdout=PIPE)
for line in iter(p.stdout.readline, ''):
print line,
There might be a buffering issue on the program' side if it prints line-by-line when run interactively but buffers its output if run as a subprocess. There are various solutions depending on your OS or the program e.g., you could run it using pexpect module.
Related
On the terminal, I have two programs to run using subprocess
First, I will call ./matrix-odas & so the first program will run in the background and I can then type the second command. The first command will return some messages.
The second command ~/odas/bin/odaslive -vc ~/odas/config/odaslive/matrix_creator.cfg will open the second program and it will keep running and keep printing out text. I'd like to use subprocess to open these programs and capture both outputs.
I have never used subprocess before and following tutorials, I am writing the script on Jupyter notebook (python 3.7) in order to see the output easily.
from subprocess import Popen, PIPE
p = Popen(["./matrix-odas", "&"], stdout=PIPE, stderr=PIPE, cwd=wd, universal_newlines=True)
stdout, stderr = p.communicate()
print(stdout)
This is the code that i tried to open the first program. But Jupyter notebook always gets stuck at p.communicate() and I can't see the messages. Without running the first program in the background, I won't be able to get the command prompt after the messages are printed.
I would like to know what subprocess function should I use to solve this issue and which platform is better to test subprocess code. Any suggestions will be appreciated. Thank you so much!
From this example at the end of this section of the docs
with Popen(["ifconfig"], stdout=PIPE) as proc:
log.write(proc.stdout.read())
it looks like you can access stdout (and I would assume stderr) from the object directly. I am not sure whether you need to use Popen as a context manager to access that property or not.
My problem is very similar to the problems described here and here with one thing not being covered: Assume, that I have an external longrunning.exe on windows, and I'm calling that with subprocess.Popen(). My exe now prints some commands and after some time, it gets into a loopback-mode and waits for input. When that happens, it outputs a single dot every second in the windows command prompt. It does put the subsequent dots on the same line, whereas all output before that is on its own line. I seem to be able to catch all output before that, but I cannot get this output, probably to some buffering going on(?). How can I get this output in my python console? Relevant code as below:
import subprocess
import sys
cmd = 'long_running.exe'
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
for line in iter(p.stdout.readline, b''):
sys.stdout.write(line)
Is there any way to use Popen with interactive commands? I mean nslookup, ftp, powershell... I read the whole subprocess documentation several times but I can't find the way.
What I have (removing the parts of the project which aren't of interest here) is:
from subprocess import call, PIPE, Popen
command = raw_input('>>> ')
command = command.split(' ')
process = Popen(command, stdout=PIPE, stderr=PIPE, shell=True)
execution = process.stdout.read()
error = process.stderr.read()
output = execution + error
process.stderr.close()
process.stdout.close()
print(output)
Basically, when I try to print the output with a command like dir, the output is a string, so I can work with the .read() on it. But when I try to use nslookup for example, the output isn't a string, so it can't be read, and the script enters in a deadlock.
I know that I can invoke nslookup in non-interactive mode, but that's not the point. I want to remove all the chances of a deadlock, and make it works with every command you can run in a normal cmd.
The real way the project works is through sockets, so the raw_input is a s.recv() and the output is sending back the output, but I have simplified it to focus on the problem.
I'm trying to run a shell program through python. I need to run a command, then while it's still running and waiting for input to continue, I need to take the output received by the program, and process that data as a string. Then I need to parse some data into that program, and simulate an enter pressing.
What would be the best way to achieve this?
subprocess.Popen will work for this, but to read and then write and then read again you can't use communicate (because this will cause the process to end).
Instead, you'll need to work with the process's output pipe (process.stdout below). This is tricky to get right, because reading on the process's stdout is blocking, so you sort of need to know when to stop trying to read (or know how much output the process is going to produce).
In this example, the subprocess is a shell script that writes a line of output, and then echoes whatever you give it until it reads EOF.
import subprocess
COMMAND_LINE = 'echo "Hello World!" ; cat'
process = subprocess.Popen(COMMAND_LINE, shell=True,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE)
s = process.stdout.readline().strip()
print(s)
s2 = process.communicate(s)[0]
print(s2)
Gives:
Hello World!
Hello World!
For more complicated cases, you might think about looking at something like pexpect.
Use subprocess.Popen to run your shell application and use communicate to interact with it.
I'm writing a simple wrapper over python debugger (pdb) and I need to parse pdb output. But I have a problem reading text from process pipe.
Example of my code:
import subprocess, threading, time
def readProcessOutput(process):
while not process.poll():
print(process.stdout.readline())
process = subprocess.Popen('python -m pdb script.py', shell=True, universal_newlines=True,
stdout=subprocess.PIPE, stderr=subprocess.STDOUT, stdin=subprocess.PIPE)
read_thread = threading.Thread(target=readProcessOutput, args=(process,))
read_thread.start()
while True:
time.sleep(0.5)
When i execute given command (python -m pdb script.py) in OS shell I get results like this:
> c:\develop\script.py(1)<module>()
-> print('hello, world!')
(Pdb)
But when i run my script i get only two lines, but can't get pdb prompt. Writing commands to stdin after this has no effect. So my question is:
why I cannot read third line? How can I avoid this problem and get correct output?
Platform: Windows XP, Python 3.3
The third line can not be read by readline() because it is not terminated yet by the end of line. You see usually the cursor after "(pdb) " until you write anything + enter.
The communication to processes that have some prompt is usually more complicated. It proved to me to write also an independent thread for data writer first for easier testing the communication in order to be sure that the main thread never freezes if too much is tried to be written or read. Then it can be simplified again.