I am new to Python. I want to make it show Ruby puts and also to make my ruby script start all over when it crashes:
import subprocess
cmd = "ruby script.rb"
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
output, errors = p.communicate()
Any help?
I don't think Python is a good solution for this problem. It's much better to write a simple CMD (if you're using Windows) or Bash (if you're using Unix-like OS) script:
#!/bin/bash
trap handler SIGINT
RUN=true
handler() {
RUN=false
}
while [ ${RUN} = true ]; do
python child.py
done
It gives you realtime output, which is much harder to achieve in Python. And automatically restarts script, when it exits.
Related
Thank you in advance for the time you'll give to read this question. I am learning Python and I looked up a lot before asking here, please forgive me for the newbie question.
So I created this script in python 3 using subprocess module to search for another python script's PID, while only knowing the beginning of the script's name and terminate it nicely.
Basically I run python clocks on my LCD screen through Raspberry and I2C, and I terminate the script, clear the LCD and turn it off. This "off" script code is provided below.
The issue is that when I run it from the directory it sits in with a:
python3 off.py
It works perfectly, getting parsing and terminating the PID, then turning off the LCD display.
Ideally I want to trigger it through telegram-cli because I did it in bash and it worked nicely, I find it to be a nice feature. In python it fails.
So I tested and it appears that when I try to launch it from another directory like this:
python3 ~/code/off.py
The grep subprocess returns more than the one PID it returns normally when launched from the script residing directory. For instance (with python3 -v):
kill: failed to parse argument: '25977
26044'
The second PID number is from a sub process created by the script, I can't seem to find what it is as it terminates when the script ends but fails it initial purpose.
Any help in understanding what is happening here would be really appreciated.
I came so far, as show below, from two ugly lines of bash mixed with a call to an dummy four lines python scripts, so I really feel I am getting close to a proper way of achieving my first real python script.
I tried to decompose the script line by line in the interpreter and could not reproduce the error, everything behave as expected. I only get this double PID result when running the script from an outer location.
Thank you in advance for any helpful insight on how to understand what is happening!
#!/usr/bin/env python3
import subprocess
import I2C_LCD_driver
import string
# Defining variables for searched strings and string encoding
searched_process_name = 'lcd_'
cut_grep_out_of_results = 'grep'
result_string_encoding = 'utf-8'
mylcd = I2C_LCD_driver.lcd()
LCD_NOBACKLIGHT = 0x00
run = True
def kill_script():
# Listing processes and getting the searched process
ps_process = subprocess.Popen(["ps", "aux"], stdout=subprocess.PIPE)
grep_process = subprocess.Popen(["grep", "-i", searched_process_name], stdin=ps_process.stdout, stdout=subprocess.PIPE)
# The .stdout.close() lines below allow the previous process to receive a SIGPIPE if the next process exits.
ps_process.stdout.close()
# Cleaning the result until only the PID number is returned in a string
grep_cutout = subprocess.Popen(["grep", "-v", cut_grep_out_of_results], stdin=grep_process.stdout, stdout=subprocess.PIPE)
grep_process.stdout.close()
awk = subprocess.Popen(["cut", "-c", "10-14"], stdin=grep_cutout.stdout, stdout=subprocess.PIPE)
grep_cutout.stdout.close()
output = awk.communicate()[0]
clean_output = output.decode(result_string_encoding)
clean_output_no_new_line = clean_output.rstrip()
clean_output_no_quote = clean_output_no_new_line.replace("'", '')
PID = clean_output_no_quote
# Terminating the LCD script process
subprocess.Popen(["kill", "-9", PID])
while run:
kill_script()
# Cleaning and shutting off LCD screen
mylcd.lcd_clear()
mylcd.lcd_device.write_cmd(LCD_NOBACKLIGHT)
break
I found out the reason of this weird comportment. An error on my end:
I forgot I called some directories with a name including the characters string I was running grep -i against provoking the double result when running the script from outside its directory using its full path.
Turns out the script runs pretty well using subprocess.
So in the end, I renamed the scripts I wanted to terminate with disp_ rather than lcd_ and added shell=False to my subprocesses to make sure there were no risk of unwantedly sending the output to bash while the running the script.
I'm new to python, still learning
What i need to do is to fork a complex command to background and continue th execution of my main program, something like this:
I do this from the linux command line (and works ok)
./pgm1 arg1 arg2 arg3 | ./pgm22 arg21 arg22 arg23 arg24 &
so the program goes to background and i can coninue my work.
How can i run the above command in my python program?
Many thanks
You can PIPE the output of the first command to the second using subprocess.Popen:
from subprocess import PIPE,Popen
p = Popen(["./pgm1" ,"arg1" ,"arg2" ,"arg3" ],stdout=PIPE)
p1 = Popen( ["./pgm22", "arg21", "arg22", "arg23" ,"arg24"],stdin=p.stdout,stdout=PIPE)
p.stdout.close()
Popen does not wait for the command to finish.
I have a python script which at one point is required to run a perl script, wait for it to finish, then continue.
As this case will only occur on a windows machine, I thought I could simply open a new cmd and run the perl script there, but I'm having difficulties doing so.
import os
os.system("start /wait cmd /c {timeout 10}")
should open a new cmd and sleep for 10 seconds, but it closes right away. I don't want to put the perl script in position of the timeout 10, as it is quite resource intensive.
Another idea was to use a subprocess with call or Popen and wait.
perl_script = subprocess.call(['script.pl', params])
But I'm not sure what would happen to the stdout of the perl script in such a case.
I know the location and the parameters of the perl script.
How can I run a perl script from my python script, print the output (a lot) and wait for it to finish?
edit:
As suggested by #rchang, I added the subprocess with communicate as following and it works just as intended.
import subprocess, sys
perl = "C:\\perl\\bin\\perl.exe"
perl_script "C:\\scripts\\perl\\flamethrower.pl"
params = " --mount-doom-hot"
pl_script = subprocess.Popen([perl, perl_script, params], stdout=sys.stdout)
pl_script.communicate()
These are my first lines of perl, just a quick copy/past script to test this.
print "Hello Perld!\n";
sleep 10;
print "Bye Perld!\n";
import subprocess
import sys
perl_script = subprocess.Popen(["script.pl", params], stdout=sys.stdout)
perl_script.communicate()
This should hook up the stdout of the subprocess to the stdout stream of the Python script, provided you won't actually need the Python script to output anything else meaningful during execution that may not be related to the subprocess output.
You could try:
perl_script = subprocess.check_output(["script.pl", params])
print perl_script
I am working on executing the shell script from Python and so far it is working fine. But I am stuck on one thing.
In my Unix machine I am executing one command in the background by using & like this. This command will start my app server -
david#machineA:/opt/kml$ /opt/kml/bin/kml_http --config=/opt/kml/config/httpd.conf.dev &
Now I need to execute the same thing from my Python script but as soon as it execute my command it never goes to else block and never prints out execute_steps::Successful, it just hangs over there.
proc = subprocess.Popen("/opt/kml/bin/kml_http --config=/opt/kml/config/httpd.conf.dev &", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, executable='/bin/bash')
if proc.returncode != 0:
logger.error("execute_steps::Errors while executing the shell script: %s" % stderr)
sleep(0.05) # delay for 50 ms
else:
logger.info("execute_steps::Successful: %s" % stdout)
Anything wrong I am doing here? I want to print out execute_steps::Successful after executing the shell script in the background.
All other command works fine but only the command which I am trying to run in background doesn't work fine.
There's a couple things going on here.
First, you're launching a shell in the background, and then telling that shell to run the program in the background. I don't know why you think you need both, but let's ignore that for now. In fact, by adding executable='/bin/bash' on top of shell=True, you're actually trying to run a shell to run a shell to run the program in the background, although that doesn't actually quite work.*
Second, you're using PIPE for the process's output and error, but then not reading them. This can cause the child to deadlock. If you don't want the output, use DEVNULL, not PIPE. If you want the output to process yourself, use proc.communicate().**, or use a higher-level function like check_output. If you just want it to intermingle with your own output, just leave those arguments off.
* If you're using the shell because kml_http is a non-executable script that has to be run by /bin/bash, then don't use shell=True for that, or executable, just make make /bin/bash the first argument in the command line, and /opt/kml/bin/kml_http the second. But this doesn't seem likely; why would you install something non-executable into a bin directory?
** Or you can read it explicitly from proc.stdout and proc.stderr, but that gets more complicated.
At any rate, the whole point of executing something in the background is that it keeps running in the background, and your script keeps running in the foreground. So, you're checking its returncode before it's finished, and then moving on to whatever's next in your code, and never coming back again.
It seems like you want to wait for it to be finished. In that case, don't run it in the background—use proc.wait, or just use subprocess.call() instead of creating a Popen object. And don't use & either, of course. While we're at it, don't use the shell, either:
retcode = subprocess.call(["/opt/kml/bin/kml_http",
"--config=/opt/kml/config/httpd.conf.dev"],
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
if retcode != 0:
# etc.
Now, you won't get to that if statement until kml_http finishes running.
If you want to wait for it to be finished, but at the same time keep doing other stuff, then you're trying to do two things at once in your program, which means you need a thread to do the waiting:
def run_kml_http():
retcode = subprocess.call(["/opt/kml/bin/kml_http",
"--config=/opt/kml/config/httpd.conf.dev"],
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
if retcode != 0:
# etc.
t = threading.Thread(target=run_kml_http)
t.start()
# Now you can do other stuff in the main thread, and the background thread will
# wait around until kml_http is finished and execute the `if` statement whenever
# that happens
You're using stderr=PIPE, stdout=PIPE which means that rather than letting the stdin and stdout of the child process be forwarded to the current process' standard output and error streams, they are being redirected to a pipe which you must read from in your python process (via proc.stdout and proc.stderr.
To "background" a process, simply omit the usage of PIPE:
#!/usr/bin/python
from subprocess import Popen
from time import sleep
proc = Popen(
['/bin/bash', '-c', 'for i in {0..10}; do echo "BASH: $i"; sleep 1; done'])
for x in range(10):
print "PYTHON: {0}".format(x)
sleep(1)
proc.wait()
which will show the process being "backgrounded".
I'm working on a small script. The script should open 3 terminals and interact with this terminals independently.
I am pretty understand that subprocess is the best way to do that. What I've done so far:
# /usr/bin/env python
import subprocess
term1 = subprocess.Popen(["open", "-a", "Terminal"], stdin=subprocess.PIPE, stdout=subprocess.PIPE)
term1.communicate(input="pwd")
My problem is I cannot interact with a new terminal. this part term1.communicate(input="pwd") is not working. I cannot send a command to a new Terminal. I also tried term1.communicate(input="pwd\n") but nothing happens
Do you any ideas how can I do that?
P.S. I am using Mac OS.
You can run both commands concurrently without opening terminals.
import subprocess
process1 = subprocess.Popen(["ls", "-l"])
process2 = subprocess.Popen(["ls", "-l"])
If you run that code you will see that the directory is listed twice, interleaved together. You can expand this for your specific needs:
tcprelay1 = subprocess.Popen(["tcprelay", "telnet"])
tcprelay2 = subprocess.Popen(["tcprelay", "--portoffset [arg1] [arg2]")