I have a c executable which gets data from a iot hardware and print information on console using printf. I want to run this executable from python which I am able to do so using subprocess.call in following way
subprocess.call(["demoProgram", "poll"])
and print the output to console. But I need to capture this output(printf) using my python code to process information further in real time. How can I capture this output using subprocess in real time?
The following opens a subprocess and creates an iterator from the output.
import subprocess
import sys
proc = subprocess.Popen(['ping','google.com'], stdout=subprocess.PIPE)
for line in iter(proc.stdout.readline, ''):
print(line) # process line-by-line
This solution was modified from the answer to a similar question.
if you're using python 2x
have a look at the commands module
import commands
output=commands.getoutput("gcc demoProgram.c") #command to be executed
print output
for python3x
use the subprocess module
import subprocess
output=subprocess.getoutput("gcc demoProgram.c") #command to be executed
print output
Related
I am trying to write the codes to run a C executable using Python.
The C program can be run in the terminal just by calling ./myprogram and it will prompt a selection menu, as shown below:
1. Login
2. Register
Now, using Python and subprocess, I write the following codes:
import subprocess
subprocess.run(["./myprogram"])
The Python program runs but it shows nothing (No errors too!). Any ideas why it is happening?
When I tried:
import subprocess
subprocess.run(["ls"])
All the files in that particular directory are showing. So I assume this is right.
You have to open the subprocess like this:
import subprocess
cmd = subprocess.Popen(['./myprogram'], stdin=subprocess.PIPE)
This means that cmd will have a .stdin you can write to; print by default sends output to your Python script's stdout, which has no connection with the subprocess' stdin. So do that:
cmd.stdin.write('1\n') # tell myprogram to select 1
and then quite probably you should:
cmd.stdin.flush() # don't let your input stay in in-memory-buffers
or
cmd.stdin.close() # if you're done with writing to the subprocess.
PS If your Python script is a long-running process on a *nix system and you notice your subprocess has ended but is still displayed as a Z (zombie) process, please check that answer.
Maybe flush stdout?
print("", flush=True,end="")
I have been trying to write a function which would execute a command passed to it thru a parameter using POPEN along with Context Managers. Unfortunately, I am unable to get it to work. Can someone please help?
import os
import sys
import subprocess
import inspect
def run_process(cmd_args):
with subprocess.Popen(cmd_args, stdout=subprocess.PIPE) as proc:
log.write(proc.stdout.read())
run_process("print('Hello')")
The output expected is "Hello". Can someone please point out where I am going wrong?
What you have done is right if you are running a bash command through the subprocess.
Inside the context manager "with ..." what you have done is to reading out the output from the terminal and storing them as byte(s) in "output" variable and trying to print out the bytes in ASCII after decoding it.
Try returning the value from the context manager and then decode it in the calling function:
import os
import sys
import subprocess
import inspect
def run_process(cmd_args): # Below added shell=True' in parameters.
with subprocess.Popen(cmd_args, stdout=subprocess.PIPE, shell=True) as proc:
return proc.stdout.read() # returns the output
# Optionally you can use the 'encoding='utf-8' argument
# instead and just print(proc.stdout.read()).
print(run_process().decode('utf-8'))
I was having a similar issue while pipelining a process to another program and I did the decoding in the other program and surprisingly it worked. Hope it works for you as well.
def run_process(cmd_args):
with subprocess.Popen(cmd_args, stdout=subprocess.PIPE) as p:
output = p.stdout.read()
return output
It worked for the same question.
Popen runs the command it receives as you would run something in your terminal (example: CMD on Windows or bash on Linux). So, it does not execute Python, but Bash code (on Linux for ex). The Python binary has a command, -c that does what you would need: executes a Python command right away. So you have to options:
either use echo Hello (works on Windows or Linux too, echo it's both
in batch and in bash)
or you could use python -c "print('Hello') instead of just the print command.
Without making too many changes to your existing script, I have edited your script with the below comments indicating what I did to get it to work. I hope this helps.
import os
import sys
import subprocess
import inspect
def run_process(cmd_args): # Below added shell=True' in parameters.
with subprocess.Popen(cmd_args, stdout=subprocess.PIPE, shell=True) as proc:
output = proc.stdout.read() # Reads the output from the process in bytes.
print(output.decode('utf-8')) # Converts bytes to UTF-8 format for readability.
# Optionally you can use the 'encoding='utf-8' argument
# instead and just print(proc.stdout.read()).
run_process("echo Hello") # To display the message in the prompt use 'echo' in your string like this.
Note: Read the Security Considerations section before using shell=True.
https://docs.python.org/3/library/subprocess.html#security-considerations
for example I run a script
os.execv('script.py',('',))
As I read in docs this command starts a script from your current script by taking it's pid and reasigning it to run script.py. So I can get the pid of process.
The question is following:
After running execv I need to get the stdout of this script, and the only thing I know is the pid of process. Is it possible to perform this with python ? Any suggestions ? I need to use only execv()
Another possible solution redirecting the output to a file.
import os,sys
sys.stdout = open("./data.out","w")
os.dup2(sys.stdout.fileno(), 1)
os.execv('/usr/bin/python', ['python', './script.py'])
os.execv is just binding to execve system call. Thing that you need is a subprocess module:
import sys
import subprocess
proc = subprocess.Popen([sys.executable, 'script.py'],
stdout = subprocess.PIPE)
proc.wait()
print(proc.stdout.read())
See https://docs.python.org/2/library/subprocess.html
I have an external executable file which I am trying to run from a Python script. CMD executable runs but without generating output. Probably it exit before output can be generated. Any suggestion about how to delay exit until outputs are generated?
import subprocess, sys
from subprocess import Popen, PIPE
exe_str = r"C:/Windows/System32/cmd C:/temp/calc.exe"
parent = subprocess.Popen(exe_str, stderr=subprocess.PIPE)
use subprocess.call, more info here:
import subprocess
subprocess.call(["C:\\temp\\calc.exe"])
or
import os
os.system('"C:/Windows/System32/notepad.exe"')
i hope it helps you...
The os.system method is depreciated and should not be used in new applications. The subprocess module is the pythonic way to do what you require.
Here is an example of some code I wrote a few weeks ago using subprocess to load files, the command you need to use to delay exit until data has been received and the launched program completes is wait():
import subprocess
cmd = "c:\\file.exe"
process = subprocess.Popen(cmd, stdout=subprocess.PIPE, creationflags=0x08000000)
process.wait()
creationflags=0x08000000 is an optional parameter which suppresses the launch of a window, which can be useful if the program you are calling does not need to be directly seen.
Option 1
import subprocess
subprocess.call('C:\Windows\System32\calc.exe')
Option 2
subprocess.Popen(['C:\Windows\System32\calc.exe'],stdout=subprocess.PIPE,stderr=subprocess.PIPE,shell=True).communicate()
Option 3
import os
os.system('C:\Windows\System32\calc.exe')
This worked for me after trying everything else:
Change the location of your python program to be the same as where the .exe is located.
And then the simple:
subprocess.call("calc.exe")
would work.
Hello I'm really new to the Python programming language and i have encountered a problem writing one script. I want to save the output from stdout that i obtain when i run a tcpdump command in a variable in a Python script, but i want the tpcdump command to run continuously because i want to gather the length from all packets transferred that get filtered by tcpdump(with the filter i wrote).
I tried :
fin, fout = os.popen4(comand)
result = fout.read()
return result
But it just hangs.
I'm guessing that it hangs because os.popen4 doesn't return until the child process exits. You should be using subprocess.Popen instead.
import subprocess
import shlex #just so you don't need break "comand" into a list yourself ;)
p=subprocess.Popen(shlex.split(comand),stdout=subprocess.PIPE)
first_line_of_output=p.stdout.readline()
second_line_of_output=p.stdout.readline()
...