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Save an output file on disk using shell commands in a django app

I am creating a script to run shell commands for simulation purposes using a web app. I want to run a shell command in a django app and then save the output to a file.
The problem I am facing is that when running the shell command, the output tries to get saved in the url that is invoked (for example: localhost:8000/projects) which is understandable.
I want to save the output to for example:
/home/myoutput/output.txt rather than /projects or /tasks
I have to run a whole script and save it's output to the txt file later but that is easy once this is done.
Tried os.chdir() function to change directory to /desiredpath already
from subprocess import run
#the function invoked from views.py
def invoke_mpiexec():
run('echo "this is a test file" > fahadTest.txt')
FileNotFoundError at /projects
Exception Type: FileNotFoundError

First I want to say that directly calling external programs from a web request in Django is a bit of an anti-pattern. The preferred approach is to use a work queue like Celery or rq, but that comes with a bit of added complexity.
That being said, you can solve your problem with the argument shell=True:
from subprocess import run
#the function invoked from views.py
def invoke_mpiexec():
run('echo "this is a test file" > fahadTest.txt', shell=True)
Here is the documentation:
If shell is True, the specified command will be executed through the
shell. This can be useful if you are using Python primarily for the
enhanced control flow it offers over most system shells and still want
convenient access to other shell features such as shell pipes,
filename wildcards, environment variable expansion, and expansion of ~
to a user’s home directory. However, note that Python itself offers
implementations of many shell-like features (in particular, glob,
fnmatch, os.walk(), os.path.expandvars(), os.path.expanduser(), and
shutil).
Note: Using shell=True can lead to security issues:
If the shell is invoked explicitly, via shell=True, it is the
application’s responsibility to ensure that all whitespace and
metacharacters are quoted appropriately to avoid shell injection
vulnerabilities.

You should use subprocess.call with stdout argument
def invoke_mpiexec():
f = open("fahadTest.txt", "w")
subprocess.call(['echo', '"this is a test file"'], stdout=f)
or use write function
def invoke_mpiexec():
f = open('fahadTest.txt', 'w')
f.write("Now the file has more content!")
f.close()

So I figured it out.
Below is the fix:
run('mkdir -p $HOME/phdata/test/ && echo "this is a test file" > $HOME/phdata/test/fahadTest.txt', shell=True)
mkdir -p creates a directory if it doesn't exist
$HOME is used to go to the home directory and from there you can
navigate to folders.
shell=True argument is required to run it as shell command
You can also create a ssh connection and run the commands/ scripts on the remote server. For this, my approach will be to create a script on the remote server, call it through my app and provide arguments to it. Another workaround which is not that good but works is to create a script on the server using the above line and then call it.

How to execute 'netsh' command through subprocess.check_output()

I am running a batch file which in turn runs a python file. I want to execute netsh command to change the IPv4 settings from static to dhcp and vice versa.
When I run the below code it executes and returns without any error
import subprocess
cmd = "netsh interface ip show config"
output = subprocess.check_output(cmd)
print output
But when I execute the this piece of code through a batch file the python file exits with exit status 1.
import subprocess
cmd = '''netsh interface ip set address "Local Area Connection 9" dhcp'''
output = subprocess.check_output(cmd)
print output
And It throws an error
Python: can't open file 'Update_DHCP.py': [Errno 2] No such file or directory
The python file and the batch file are in same folder and as per my understanding of updating the dhcp Ip, requires admin rights. I am even running the .bat file as 'Run as Administrator' but got the error [Errno 2]
I have also tried to create a task using task scheduler to grant admin rights to the .bat file and run it. But still, it din't work for me.
Can any one help me execute the command using subprocess.check_output() as I want to use the output returned by the check_output() call. Any help would be appreciated.
I am working on Windows and my python version is 2.7

Connecting in SSH in a Python script

I am connected to a first Raspberry Pi (172.18.x.x) in SSH and I would like to launch a script on the first RPI but the script is on another Raspberry Pi (192.168.x.x).
First, I did the configuration to connect without password to the second RPI from the first one.
When I am on the first one, I am launching this command :
ssh pi#192.168.x.x 'sudo python script_RPI2.py'
And this is working correctly, I can check the correct results but I would like to launch this script in another script on the first RPI. So, I put the previous command in the file : script_RPI1.py.
Then, I am launching the script : sudo python script_RPI1.py
And I got the following error :
ssh pi#192.168.x.x
^
SyntaxError: invalid syntax
Anyone has an idea concerning my problem ?

How are you launching the script? What appears from the minimal information you gave is that you are trying or to do that command within the Python interactive interpreter or that you want to execute it in the interpreter and you forgot to surround it with quotes(") in order to make it as a string.
Try to explain a bit more please.
You want to run a bash command:
ssh pi#192.168.x.x 'sudo python script_RPI2.py'
you show do it in a .sh file as in the following example:
#!/bin/sh
ssh pi#192.168.x.x 'sudo python script_RPI2.py'
After saving this file just do ./name_of_file.sh, which will simply run your bash file in the terminal, if you want to run a python script that opens a terminal in another process and executes string that are terminal commands you should look at something like this:
from subprocess import call
call(["ls"])
This will execute ls in another terminal process and return the result back to you. Please check what you want to actually do and decide on one of these paths.

Modified the entire answer and actually put some extra time on the code. The full solution for you to integrate will look something like the code below. Note that the code is setup in a way that you can define the host to connect to, along with the command you want to execute in the remote RPi
import subprocess
import sys
remoteHost="pi#192.168.x.x"
command="python /path/to/script.py"
ssh = subprocess.Popen(["ssh", "%s" % remoteHost, command],
shell=False,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE)
result = ssh.stdout.readlines()
if result == []:
error = ssh.stderr.readlines()
print >>sys.stderr, "ERROR: %s" % error
else:
print result
yourVar = result ### This is where you assign the remote result to a variable

How to call a self-defined command line function in Python

I'm trying to call a self-defined command line function in python. I defined my function using apple script in /.bash_profile as follows:
function vpn-connect {
/usr/bin/env osascript <<-EOF
tell application "System Events"
tell current location of network preferences
set VPN to service "YESVPN" -- your VPN name here
if exists VPN then connect VPN
repeat while (current configuration of VPN is not connected)
delay 1
end repeat
end tell
end tell
EOF
}
And when I tested $ vpn-connect in bash, vpn-connect works fine. My vpn connection is good.
So I created vpn.py which has following code:
import os
os.system("echo 'It is running.'")
os.system("vpn-connect")
I run it with python vpn.py and got the following output:
vpn Choushishi$ python vpn.py
It is running.
sh: vpn-connect: command not found
This proves calling self-defined function is somehow different from calling the ones that's pre-defined by the system. I have looked into pydoc os but couldn't find useful information.

A way would be to read the ./bash_profile before. As #anishsane pointed out you can do this:
vpn=subprocess.Popen(["bash"],shell=True,stdin= subprocess.PIPE)
vpn.communicate("source /Users/YOUR_USER_NAME/.bash_profile;vpn-connect")
or with os.system
os.system('bash -c "source /Users/YOUR_USER_NAME/.bash_profile;vpn-connect"')
Or try
import subprocess
subprocess.call(['vpn-connect'], shell = True)
and try
import os
os.system('bash -c vpn-connect')
according to http://linux.die.net/man/1/bash

Create an alias in bash when exiting a python script

I have written a shell in python (using the cmd module) and when using this shell, certain information about commands run ect. is outputted to a text file. I would like to write a piece of code that creates an alias to view the text file in my bash shell (eg as if I had executed the following command:
alias latest.trc='less <path to file>
My best current effort is:
x="alias %s = 'less %s'" % (<alias name>, <path>)
y=shlex.split(x)
atexit.register(subprocess.call, y)
This works to execute some commands on exit, eg if x="echo 'bye'" but I get the error
OSError: [Errno 2] No such file or directory
The path I am entering is certainly valid and if I run x directly from the command line it works.
Any help either with why my code is hitting an error or a better way to achieve the same effect would be greatly appreciated.

You get an error because alias is a bash command, not an executable. You must run subprocess.call inside a shell:
import subprocess
import atexit
import shlex
x="alias %s = 'less %s'" % ('a', 'whatever')
y=shlex.split(x)
atexit.register(lambda args: subprocess.call(args, shell=True), y)
But, given the fact that subprocess spawns a new process, whatever changes are made to the environment it runs into, are lost on exit.
You'd better instead create a file where you put all these aliases and source it by hand when you need to use them.