I am currently trying to utilize strace to automatically trace a programm 's system calls. To then parse and process the data obtained, I want to use a Python script.
I now wonder, how would I go about calling strace from Python?
Strace is usually called via command line and I don't know of any C library compiled from strace which I could utilize.
What is the general way to simulate an access via command line via Python?
alternatively: are there any tools similar to strace written natively in Python?
I'm thankful for any kind of help.
Nothing, as I'm clueless
You need to use the subprocess module.
It has check_output to read the output and put it in a variable, and check_call to just check the exit code.
If you want to run a shell script you can write it all in a string and set shell=True, otherwise just put the parameters as strings in a list.
import subprocess
# Single process
subprocess.check_output(['fortune', '-m', 'ciao'])
# Run it in a shell
subprocess.check_output('fortune | grep a', shell=True)
Remember that if you run stuff in a shell, if you don't escape properly and allow user data to go in your string, it's easy to make security holes. It is better to not use shell=True.
You can use commands as the following:
import commands
cmd = "strace command"
result = commands.getstatusoutput(cmd)
if result[0] == 0:
print result[1]
else:
print "Something went wrong executing your command"
result[0] contains the return code, and result[1] contains the output.
Python 2 and Python 3 (prior 3.5)
Simply execute:
subprocess.call(["strace", "command"])
Execute and return the output for processing:
output = subprocess.check_output(["strace", "command"])
Reference: https://docs.python.org/2/library/subprocess.html
Python 3.5+
output = subprocess.run(["strace", "command"], caputure_output=True)
Reference: https://docs.python.org/3.7/library/subprocess.html#subprocess.run
Related
This is a follow up on a previous question as I have made progress(which is irrelevant at this point). It is worth noting that I am learning python and barely know what I am doing, however, I am familiar with programming. I am trying to call an SCP command in the windows terminal through python. However, it is not doing the desired effect. The script runs smoothly with no errors and it prints the debug commands as I have written them. However, the SCP call does not actually go through on the other end. To make sure I have the right command, I have it set to print the same command that it called afterwards. When I copy this printed command and paste it into the windows command terminal, it gives the desired effect. Why is the same command not working correctly in python? Thanks. This is my script:
import subprocess
subprocess.run(['scp', 'c:/users/<name>/desktop/OOGA.txt', 'pi#<IP>:here/'], shell=True)
print ("done")
print ('scp', 'c:/users/<name>/desktop/OOGA.txt', 'pi#<IP>:here/')
Try using raw string if shell is set to True:
from subprocess import run as subrun
status = subrun(r'scp c:/users/<name>/desktop/OOGA.txt pi#<IP>:here/',shell=True)
print("Done")
print(status)
In Python 3.7 running on Windows, what specific syntax is required to:
1. Navigate to a directory containing a terraform program
2. Execute "terraform apply -auto-approve" in that target directory
3. Extract the resulting output variables into a form usable in python
The output variables might take the form:
security_group_id_nodes = sg-xxxxxxxxxx
vpc_id_myvpc = vpc-xxxxxxxxxxxxx
Want to be using windows cmd style commands here, NOT powershell.
My first failed newbie attempt is:
import os
os.chdir('C:\\path\\to\\terraform\\code')
from subprocess import check_output
check_output("terraform apply -auto-approve", shell=True).decode()
Not sure about your output, but subprocess could definitely make the trick.
Try something like:
command = 'terraform apply -auto-approve'
TARGET_DIR = 'E:\Target\Directory'
subprocess_handle = subprocess.Popen(shlex.split(command), cwd=TARGET_DIR, shell=False, stdout=subprocess.PIPE)
subprocess_handle.wait()
result = subprocess_handle.communicate()[0]
print(result)
Worked for me once, just play around with params.
UPD: Here I assume that "terraform" is an executable.
I was using python project pick to select an option from a list. Below code returns the option and index.
option, index = pick(options, title)
Pick uses curses library from python. I want to pass the output of my python script to shell script.
variable output = $(pythonfile.py)
but it gets stuck on the curses screen. It cannot draw anything. What can be the reason for this?
pick gets stuck because when you use $(pythonfile.py), the shell redirects the output of pythonfile.py as if it were a pipe. Also, the output of pick contains characters for updating the screen (not what you want). You can work around those problems by
redirecting the output of pythonfile.py to /dev/tty
ensuring that your pythonfile.py writes its result to the standard error, and
directing the standard error in the shell script to the output of the $(...) construct.
For example:
#!/bin/bash
foo=$(python basic.py 2>&1 >/dev/tty )
echo "result '$foo'"
and in pythonfile.py, doing
import sys
print(option, index, file=sys.stderr)
rather than
print(option, index)
To pass the output of a Python script to a Bash variable you need to specify the command with which to open the python file inside the variable's declaration.
Like so:
variable_output=$(python pythonfile.py)
Furthermore, if you'd like to pass a variable from Python to bash you could use Python's sys module and then redirect the stderr.
Like so:
test.py
import sys
test_var = (str(3 + 3))
sys.exit(test_var)
test.sh
test_var=$(python3 test.py 2>&1)
echo $testvar
Now, if we run test.sh we get the output 6.
Running into issues executing a PowerShell script from within Python.
The Python itself is simple, but it seems to be passing in \n when invoked and errors out.
['powershell.exe -ExecutionPolicy Bypass -File', '$Username = "test";\n$Password = "password";\n$URL
This is the code in full:
import os
import subprocess
import urllib2
fetch = urllib2.urlopen('https://raw.githubusercontent.com/test')
script = fetch.read()
command = ['powershell.exe -ExecutionPolicy Bypass -File', script]
print command #<--- this is where I see the \n.
#\n does not appear when I simply 'print script'
So I have two questions:
How do I correctly store the script as a variable without writing to disk while avoiding \n?
What is the correct way to invoke PowerShell from within Python so that it would run the script stored in $script?
How do I correctly store the script as a variable without writing to disk while avoiding \n?
This question is essentially a duplicate of this one. With your example it would be okay to simply remove the newlines. A safer option would be to replace them with semicolons.
script = fetch.read().replace('\n', ';')
What is the correct way to invoke PowerShell from within Python so that it would run the script stored in $script?
Your command must be passed as an array. Also you cannot run a sequence of PowerShell statements via the -File parameter. Use -Command instead:
rc = subprocess.call(['powershell.exe', '-ExecutionPolicy', 'Bypass', '-Command', script])
I believe this is happening because you are opening up PowerShell and it is automatically formatting it a specific way.
You could possibly do a for loop that goes through the command output and print without a /n.
I'm trying to execute unfluff inside a python script using subprocess, but the result is always empty.
If I execute it from the shell, it goes ok. Here is an example:
From the unfluff documentation I can extract the contents of a webpage through:
curl -s 'http://observador.pt/2016/10/29/espanha-e-portugal-sao-unicos-paises-da-ue-sem-populismo-xenofobo-diz-antonio-costa' | unfluff
This results in a nice json with a good content extraction.
Now, in python I'm using the following:
import subprocess
url = 'http://observador.pt/2016/10/29/espanha-e-portugal-sao-unicos-paises-da-ue-sem-populismo-xenofobo-diz-antonio-costa'
p = subprocess.Popen(['curl','-s',url,'|','unfluff'],stdout=subprocess.PIPE)
print p.communicate()[0]
which results in an empty string.
So, what am I doing wrong?
By using | in your command you're implicitly invoking the OS shell.
So you have to enable shell=True to do that.
p = subprocess.Popen(['curl','-s',url,'|','unfluff'],stdout=subprocess.PIPE,shell=True)
Note: since you have Popen you could do it in a much cleaner way by opening 2 Popen instances, for instance like this:
p1 = subprocess.Popen(['curl','-s',url],stdout=subprocess.PIPE)
p2 = subprocess.Popen('unfluff',stdin=p1.stdout,stdout=subprocess.PIPE)
print(p2.communicate()[0])
(then you don't need the shell=True parameter, EDIT: you still need the shell=True parameter on the second Popen probably because unfluff is not really an executable, so needs the shell to start)
the rule is: if you want to be safe, always set shell=True but the command line then depends on the OS shell and it's less efficient. So if it works without it, it's better.