I have time consuming SNMP walk task to perform which I am running as a background process using Popen command. How can I capture the output of this background task in a log file. In the below code, I am trying to do snampwalk on each IP in ip_list and logging all the results to abc.txt. However, I see the generated file abc.txt is empty.
Here is my sample code below -
import subprocess
import sys
f = open('abc.txt', 'a+')
ip_list = ["192.163.1.104", "192.163.1.103", "192.163.1.101"]
for ip in ip_list:
cmd = "snmpwalk.exe -t 1 -v2c -c public "
cmd = cmd + ip
print(cmd)
p = subprocess.Popen(cmd, shell=True, stdout=f)
p.wait()
f.close()
print("File output - " + open('abc.txt', 'r').read())
the sample output from the command can be something like this for each IP -
sysDescr.0 = STRING: Software: Whistler Version 5.1 Service Pack 2 (Build 2600)
sysObjectID.0 = OID: win32
sysUpTimeInstance = Timeticks: (15535) 0:02:35.35
sysContact.0 = STRING: unknown
sysName.0 = STRING: UDLDEV
sysLocation.0 = STRING: unknown
sysServices.0 = INTEGER: 72
sysORID.4 = OID: snmpMPDCompliance
I have already tried Popen. But it does not logs output to a file if it is a time consuming background process. However, it works when I try to run background process like ls/dir. Any help is appreciated.
The main issue here is the expectation of what Popen does and how it works I assume.
p.wait() here will wait for the process to finish before continuing, that is why ls for instance works but more time consuming tasks doesn't. And there's nothing flushing the output automatically until you call p.stdout.flush().
The way you've set it up is more meant to work for:
Execute command
Wait for exit
Catch output
And then work with it. For your usecase, you'd better off using an alternative library or use the stdout=subprocess.PIPE and catch it yourself. Which would mean something along the lines of:
import subprocess
import sys
ip_list = ["192.163.1.104", "192.163.1.103", "192.163.1.101"]
with open('abc.txt', 'a+') as output:
for ip in ip_list:
print(cmd := f"snmpwalk.exe -t 1 -v2c -c public {ip}")
process = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE) # Be wary of shell=True
while process.poll() is None:
for c in iter(lambda: process.stdout.read(1), ''):
if c != '':
output.write(c)
with open('abc.txt', 'r') as log:
print("File output: " + log.read())
The key things to take away here is process.poll() which checks if the process has finished, if not, we'll try to catch the output with process.stdout.read(1) to read one byte at a time. If you know there's new lines coming, you can switch those three lines to output.write(process.stdout.readline()) and you're all set.
Related
I am running a script that iterates through a text file. On each line on the text file there is an ip adress. The script grabs the banner, then writes the ip + banner on another file.
The problem is, it just stops around 500 lines, more or less, with no error.
Another weird thing is if i run it with python3 it does what i said above. If i run it with python it iterates through those 500 lines, then starts at the beggining. I noticed this when i saw repetitions in my output file. Anyway here is the code, maybe you guys can tell me what im doing wrong:
import os
import subprocess
import concurrent.futures
#import time, random
import threading
import multiprocessing
with open("ipuri666.txt") as f:
def multiprocessing_func():
try:
line2 = line.rstrip('\r\n')
a = subprocess.Popen(["curl", "-I", line2, "--connect-timeout", "1", "--max-time", "1"], stdout=subprocess.PIPE)
b = subprocess.Popen(["grep", "Server"], stdin=a.stdout, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
#a.stdout.close()
out, err = b.communicate()
g = open("IP_BANNER2","a")
print( "out: {0}".format(out))
g.write(line2 + " " + "out: {0}\n".format(out))
print("err: {0}".format(err))
except IOError:
print("Connection timed out")
if __name__ == '__main__':
#starttime = time.time()
processes = []
for line in f:
p = multiprocessing.Process(target=multiprocessing_func, args=())
processes.append(p)
p.start()
for process in processes:
process.join()
If your use case allows I would recommend just rewriting this as a shell script, there is no need to use Python. (This would likely solve your issue indirectly.)
#!/usr/bin/env bash
readarray -t ips < ipuri666.txt
for ip in ${ips[#]}; do
output=$(curl -I "$ip" --connect-timeout 1 --max-time 1 | grep "Server")
echo "$ip $output" >> fisier.txt
done
The script is slightly simpler than what you are trying to do, for instance I do not capture the error. This should be pretty close to what you are trying to accomplish. I will update again if needed.
This question already has answers here:
Running shell command and capturing the output
(21 answers)
Closed 4 years ago.
I'm using python 3.7 on Windows. I'm trying to execute a simple scan command and get its output as a string.
When I execute the command in python I only get the first line:
import subprocess
def execute(command):
proc = subprocess.run(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True)
output = proc.stdout if proc.stdout else proc.stderr
path = "Somepath"
command = ['ecls.exe', '/files', path]
print(execute(command))
output:
WARNING! The scanner was run in the account of a limited user.
But when I run it in the CMD:
$ ecls.exe /files "SomePath"
WARNING! The scanner was run in the account of a limited user.
ECLS Command-line scanner ...
Command line: /files SomePath
Scan started at: 11/24/18 14:18:11
Scan completed at: 11/24/18 14:18:11 Scan time: 0 sec (0:00:00)
Total: files - 1, objects 1 Infected: files - 0, objects 0 Cleaned: files - 0, objects 0
I think that the command spawn a child process and it produces the scan output. I also tried to iterate over stdout but got the same output.
EDIT:
I tried other methods like check_output, Popen, etc with using PIPE but I only get the first line of output. I also tried to use shell=True but didn't make any difference. As I already said the command spawn a child process and I need to capture its output which seems that subprocess can't do it directly.
As I couldn't find a direct way to solve this problem, with help of this reference, the output can be redirected to a text file and then read it back.
import subprocess
import os
import tempfile
def execute_to_file(command):
"""
This function execute the command
and pass its output to a tempfile then read it back
It is usefull for process that deploy child process
"""
temp_file = tempfile.NamedTemporaryFile(delete=False)
temp_file.close()
path = temp_file.name
command = command + " > " + path
proc = subprocess.run(command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True)
if proc.stderr:
# if command failed return
os.unlink(path)
return
with open(path, 'r') as f:
data = f.read()
os.unlink(path)
return data
if __name__ == "__main__":
path = "Somepath"
command = 'ecls.exe /files ' + path
print(execute(command))
I am trying to assign the output of a command to a variable without the command thinking that it is being piped. The reason for this is that the command in question gives unformatted text as output if it is being piped, but it gives color formatted text if it is being run from the terminal. I need to get this color formatted text.
So far I've tried a few things. I've tried Popen like so:
output = subprocess.Popen(command, stdout=subprocess.PIPE)
output = output.communicate()[0]
output = output.decode()
print(output)
This will let me print the output, but it gives me the unformatted output that I get when the command is piped. That makes sense, as I'm piping it here in the Python code. But I am curious if there is a way to assign the output of this command, directly to a variable, without the command running the piped version of itself.
I have also tried the following version that relies on check_output instead:
output = subprocess.check_output(command)
output = output.decode()
print(output)
And again I get the same unformatted output that the command returns when the command is piped.
Is there a way to get the formatted output, the output the command would normally give from the terminal, when it is not being piped?
Using pexpect:
2.py:
import sys
if sys.stdout.isatty():
print('hello')
else:
print('goodbye')
subprocess:
import subprocess
p = subprocess.Popen(
['python3.4', '2.py'],
stdout=subprocess.PIPE
)
print(p.stdout.read())
--output:--
goodbye
pexpect:
import pexpect
child = pexpect.spawn('python3.4 2.py')
child.expect(pexpect.EOF)
print(child.before) #Print all the output before the expectation.
--output:--
hello
Here it is with grep --colour=auto:
import subprocess
p = subprocess.Popen(
['grep', '--colour=auto', 'hello', 'data.txt'],
stdout=subprocess.PIPE
)
print(p.stdout.read())
import pexpect
child = pexpect.spawn('grep --colour=auto hello data.txt')
child.expect(pexpect.EOF)
print(child.before)
--output:--
b'hello world\n'
b'\x1b[01;31mhello\x1b[00m world\r\n'
Yes, you can use the pty module.
>>> import subprocess
>>> p = subprocess.Popen(["ls", "--color=auto"], stdout=subprocess.PIPE)
>>> p.communicate()[0]
# Output does not appear in colour
With pty:
import subprocess
import pty
import os
master, slave = pty.openpty()
p = subprocess.Popen(["ls", "--color=auto"], stdout=slave)
p.communicate()
print(os.read(master, 100)) # Print 100 bytes
# Prints with colour formatting info
Note from the docs:
Because pseudo-terminal handling is highly platform dependent, there
is code to do it only for Linux. (The Linux code is supposed to work
on other platforms, but hasn’t been tested yet.)
A less than beautiful way of reading the whole output to the end in one go:
def num_bytes_readable(fd):
import array
import fcntl
import termios
buf = array.array('i', [0])
if fcntl.ioctl(fd, termios.FIONREAD, buf, 1) == -1:
raise Exception("We really should have had data")
return buf[0]
print(os.read(master, num_bytes_readable(master)))
Edit: nicer way of getting the content at once thanks to #Antti Haapala:
os.close(slave)
f = os.fdopen(master)
print(f.read())
Edit: people are right to point out that this will deadlock if the process generates a large output, so #Antti Haapala's answer is better.
A working polyglot example (works the same for Python 2 and Python 3), using pty.
import subprocess
import pty
import os
import sys
master, slave = pty.openpty()
# direct stderr also to the pty!
process = subprocess.Popen(
['ls', '-al', '--color=auto'],
stdout=slave,
stderr=subprocess.STDOUT
)
# close the slave descriptor! otherwise we will
# hang forever waiting for input
os.close(slave)
def reader(fd):
try:
while True:
buffer = os.read(fd, 1024)
if not buffer:
return
yield buffer
# Unfortunately with a pty, an
# IOError will be thrown at EOF
# On Python 2, OSError will be thrown instead.
except (IOError, OSError) as e:
pass
# read chunks (yields bytes)
for i in reader(master):
# and write them to stdout file descriptor
os.write(1, b'<chunk>' + i + b'</chunk>')
Many programs automatically turn off colour printing codes when they detect they are not connected directly to a terminal. Many programs will have a flag so you can force colour output. You could add this flag to your process call. For example:
grep "search term" inputfile.txt
# prints colour to the terminal in most OSes
grep "search term" inputfile.txt | less
# output goes to less rather than terminal, so colour is turned off
grep "search term" inputfile.txt --color | less
# forces colour output even when not connected to terminal
Be warned though. The actual colour output is done by the terminal. The terminal interprets special character espace codes and changes the text colour and background color accordingly. Without the terminal to interpret the colour codes you will just see the text in black with these escape codes interspersed throughout.
I need to write a script in Linux which can start a background process using one command and stop the process using another.
The specific application is to take userspace and kernel logs for android.
following command should start taking logs
$ mylogscript start
following command should stop the logging
$ mylogscript stop
Also, the commands should not block the terminal. For example, once I send the start command, the script run in background and I should be able to do other work on terminal.
Any pointers on how to implement this in perl or python would be helpful.
EDIT:
Solved: https://stackoverflow.com/a/14596380/443889
I got the solution to my problem. Solution essentially includes starting a subprocess in python and sending a signal to kill the process when done.
Here is the code for reference:
#!/usr/bin/python
import subprocess
import sys
import os
import signal
U_LOG_FILE_PATH = "u.log"
K_LOG_FILE_PATH = "k.log"
U_COMMAND = "adb logcat > " + U_LOG_FILE_PATH
K_COMMAND = "adb shell cat /proc/kmsg > " + K_LOG_FILE_PATH
LOG_PID_PATH="log-pid"
def start_log():
if(os.path.isfile(LOG_PID_PATH) == True):
print "log process already started, found file: ", LOG_PID_PATH
return
file = open(LOG_PID_PATH, "w")
print "starting log process: ", U_COMMAND
proc = subprocess.Popen(U_COMMAND,
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
print "log process1 id = ", proc.pid
file.write(str(proc.pid) + "\n")
print "starting log process: ", K_COMMAND
proc = subprocess.Popen(K_COMMAND,
stdout=subprocess.PIPE, stderr=subprocess.PIPE,
shell=True, preexec_fn=os.setsid)
print "log process2 id = ", proc.pid
file.write(str(proc.pid) + "\n")
file.close()
def stop_log():
if(os.path.isfile(LOG_PID_PATH) != True):
print "log process not started, can not find file: ", LOG_PID_PATH
return
print "terminating log processes"
file = open(LOG_PID_PATH, "r")
log_pid1 = int(file.readline())
log_pid2 = int(file.readline())
file.close()
print "log-pid1 = ", log_pid1
print "log-pid2 = ", log_pid2
os.killpg(log_pid1, signal.SIGTERM)
print "logprocess1 killed"
os.killpg(log_pid2, signal.SIGTERM)
print "logprocess2 killed"
subprocess.call("rm " + LOG_PID_PATH, shell=True)
def print_usage(str):
print "usage: ", str, "[start|stop]"
# Main script
if(len(sys.argv) != 2):
print_usage(sys.argv[0])
sys.exit(1)
if(sys.argv[1] == "start"):
start_log()
elif(sys.argv[1] == "stop"):
stop_log()
else:
print_usage(sys.argv[0])
sys.exit(1)
sys.exit(0)
There are a couple of different approaches you can take on this:
1. Signal - you use a signal handler, and use, typically "SIGHUP" to signal the process to restart ("start"), SIGTERM to stop it ("stop").
2. Use a named pipe or other IPC mechanism. The background process has a separate thread that simply reads from the pipe, and when something comes in, acts on it. This method relies on having a separate executable file that opens the pipe, and sends messages ("start", "stop", "set loglevel 1" or whatever you fancy).
I'm sorry, I haven't implemented either of these in Python [and perl I haven't really written anything in], but I doubt it's very hard - there's bound to be a ready-made set of python code to deal with named pipes.
Edit: Another method that just struck me is that you simply daemonise the program at start, and then let the "stop" version find your deamonized process [e.g. by reading the "pidfile" that you stashed somewhere suitable], and then sends a SIGTERM for it to terminate.
I don't know if this is the optimum way to do it in perl, but for example:
system("sleep 60 &")
This starts a background process that will sleep for 60 seconds without blocking the terminal. The ampersand in shell means to do something in the background.
A simple mechanism for telling the process when to stop is to have it periodically check for the existence of a certain file. If the file exists, it exits.
I want to subprocess.Popen() rsync.exe in Windows, and print the stdout in Python.
My code works, but it doesn't catch the progress until a file transfer is done! I want to print the progress for each file in real time.
Using Python 3.1 now since I heard it should be better at handling IO.
import subprocess, time, os, sys
cmd = "rsync.exe -vaz -P source/ dest/"
p, line = True, 'start'
p = subprocess.Popen(cmd,
shell=True,
bufsize=64,
stdin=subprocess.PIPE,
stderr=subprocess.PIPE,
stdout=subprocess.PIPE)
for line in p.stdout:
print(">>> " + str(line.rstrip()))
p.stdout.flush()
Some rules of thumb for subprocess.
Never use shell=True. It needlessly invokes an extra shell process to call your program.
When calling processes, arguments are passed around as lists. sys.argv in python is a list, and so is argv in C. So you pass a list to Popen to call subprocesses, not a string.
Don't redirect stderr to a PIPE when you're not reading it.
Don't redirect stdin when you're not writing to it.
Example:
import subprocess, time, os, sys
cmd = ["rsync.exe", "-vaz", "-P", "source/" ,"dest/"]
p = subprocess.Popen(cmd,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
for line in iter(p.stdout.readline, b''):
print(">>> " + line.rstrip())
That said, it is probable that rsync buffers its output when it detects that it is connected to a pipe instead of a terminal. This is the default behavior - when connected to a pipe, programs must explicitly flush stdout for realtime results, otherwise standard C library will buffer.
To test for that, try running this instead:
cmd = [sys.executable, 'test_out.py']
and create a test_out.py file with the contents:
import sys
import time
print ("Hello")
sys.stdout.flush()
time.sleep(10)
print ("World")
Executing that subprocess should give you "Hello" and wait 10 seconds before giving "World". If that happens with the python code above and not with rsync, that means rsync itself is buffering output, so you are out of luck.
A solution would be to connect direct to a pty, using something like pexpect.
I know this is an old topic, but there is a solution now. Call the rsync with option --outbuf=L. Example:
cmd=['rsync', '-arzv','--backup','--outbuf=L','source/','dest']
p = subprocess.Popen(cmd,
stdout=subprocess.PIPE)
for line in iter(p.stdout.readline, b''):
print '>>> {}'.format(line.rstrip())
Depending on the use case, you might also want to disable the buffering in the subprocess itself.
If the subprocess will be a Python process, you could do this before the call:
os.environ["PYTHONUNBUFFERED"] = "1"
Or alternatively pass this in the env argument to Popen.
Otherwise, if you are on Linux/Unix, you can use the stdbuf tool. E.g. like:
cmd = ["stdbuf", "-oL"] + cmd
See also here about stdbuf or other options.
On Linux, I had the same problem of getting rid of the buffering. I finally used "stdbuf -o0" (or, unbuffer from expect) to get rid of the PIPE buffering.
proc = Popen(['stdbuf', '-o0'] + cmd, stdout=PIPE, stderr=PIPE)
stdout = proc.stdout
I could then use select.select on stdout.
See also https://unix.stackexchange.com/questions/25372/
for line in p.stdout:
...
always blocks until the next line-feed.
For "real-time" behaviour you have to do something like this:
while True:
inchar = p.stdout.read(1)
if inchar: #neither empty string nor None
print(str(inchar), end='') #or end=None to flush immediately
else:
print('') #flush for implicit line-buffering
break
The while-loop is left when the child process closes its stdout or exits.
read()/read(-1) would block until the child process closed its stdout or exited.
Your problem is:
for line in p.stdout:
print(">>> " + str(line.rstrip()))
p.stdout.flush()
the iterator itself has extra buffering.
Try doing like this:
while True:
line = p.stdout.readline()
if not line:
break
print line
You cannot get stdout to print unbuffered to a pipe (unless you can rewrite the program that prints to stdout), so here is my solution:
Redirect stdout to sterr, which is not buffered. '<cmd> 1>&2' should do it. Open the process as follows: myproc = subprocess.Popen('<cmd> 1>&2', stderr=subprocess.PIPE)
You cannot distinguish from stdout or stderr, but you get all output immediately.
Hope this helps anyone tackling this problem.
To avoid caching of output you might wanna try pexpect,
child = pexpect.spawn(launchcmd,args,timeout=None)
while True:
try:
child.expect('\n')
print(child.before)
except pexpect.EOF:
break
PS : I know this question is pretty old, still providing the solution which worked for me.
PPS: got this answer from another question
p = subprocess.Popen(command,
bufsize=0,
universal_newlines=True)
I am writing a GUI for rsync in python, and have the same probelms. This problem has troubled me for several days until i find this in pyDoc.
If universal_newlines is True, the file objects stdout and stderr are opened as text files in universal newlines mode. Lines may be terminated by any of '\n', the Unix end-of-line convention, '\r', the old Macintosh convention or '\r\n', the Windows convention. All of these external representations are seen as '\n' by the Python program.
It seems that rsync will output '\r' when translate is going on.
if you run something like this in a thread and save the ffmpeg_time property in a property of a method so you can access it, it would work very nice
I get outputs like this:
output be like if you use threading in tkinter
input = 'path/input_file.mp4'
output = 'path/input_file.mp4'
command = "ffmpeg -y -v quiet -stats -i \"" + str(input) + "\" -metadata title=\"#alaa_sanatisharif\" -preset ultrafast -vcodec copy -r 50 -vsync 1 -async 1 \"" + output + "\""
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.STDOUT, universal_newlines=True, shell=True)
for line in self.process.stdout:
reg = re.search('\d\d:\d\d:\d\d', line)
ffmpeg_time = reg.group(0) if reg else ''
print(ffmpeg_time)
Change the stdout from the rsync process to be unbuffered.
p = subprocess.Popen(cmd,
shell=True,
bufsize=0, # 0=unbuffered, 1=line-buffered, else buffer-size
stdin=subprocess.PIPE,
stderr=subprocess.PIPE,
stdout=subprocess.PIPE)
I've noticed that there is no mention of using a temporary file as intermediate. The following gets around the buffering issues by outputting to a temporary file and allows you to parse the data coming from rsync without connecting to a pty. I tested the following on a linux box, and the output of rsync tends to differ across platforms, so the regular expressions to parse the output may vary:
import subprocess, time, tempfile, re
pipe_output, file_name = tempfile.TemporaryFile()
cmd = ["rsync", "-vaz", "-P", "/src/" ,"/dest"]
p = subprocess.Popen(cmd, stdout=pipe_output,
stderr=subprocess.STDOUT)
while p.poll() is None:
# p.poll() returns None while the program is still running
# sleep for 1 second
time.sleep(1)
last_line = open(file_name).readlines()
# it's possible that it hasn't output yet, so continue
if len(last_line) == 0: continue
last_line = last_line[-1]
# Matching to "[bytes downloaded] number% [speed] number:number:number"
match_it = re.match(".* ([0-9]*)%.* ([0-9]*:[0-9]*:[0-9]*).*", last_line)
if not match_it: continue
# in this case, the percentage is stored in match_it.group(1),
# time in match_it.group(2). We could do something with it here...
In Python 3, here's a solution, which takes a command off the command line and delivers real-time nicely decoded strings as they are received.
Receiver (receiver.py):
import subprocess
import sys
cmd = sys.argv[1:]
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
for line in p.stdout:
print("received: {}".format(line.rstrip().decode("utf-8")))
Example simple program that could generate real-time output (dummy_out.py):
import time
import sys
for i in range(5):
print("hello {}".format(i))
sys.stdout.flush()
time.sleep(1)
Output:
$python receiver.py python dummy_out.py
received: hello 0
received: hello 1
received: hello 2
received: hello 3
received: hello 4