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I have a bash script that sets an environment variable an runs a command

LD_LIBRARY_PATH=my_path
sqsub -np $1 /homedir/anotherdir/executable

Now I want to use python instead of bash, because I want to compute some of the arguments that I am passing to the command.

I have tried

putenv("LD_LIBRARY_PATH", "my_path")

and

call("export LD_LIBRARY_PATH=my_path")

followed by

call("sqsub -np " + var1 + "/homedir/anotherdir/executable")

but always the program gives up because LD_LIBRARY_PATH is not set.

How can I fix this?

Thanks for help!

(if I export LD_LIBRARY_PATH before calling the python script everything works, but I would like python to determine the path and set the environment variable to the correct value)

bash:

LD_LIBRARY_PATH=my_path
sqsub -np $1 /path/to/executable

Similar, in Python:

import os
import subprocess
import sys

os.environ['LD_LIBRARY_PATH'] = "my_path" # visible in this process + all children
subprocess.check_call(['sqsub', '-np', sys.argv[1], '/path/to/executable'],
                      env=dict(os.environ, SQSUB_VAR="visible in this subprocess"))

Set and Use Environment Variable inside Python Script, It is somewhat difficult when it comes to setting and using bash environment variables in python script file. The same step is very easy and  When that command finishes, the shell goes away, and so does the environment variable. Setting it using os.putenv or os.environ has a similar effect; the environment variables are set for the Python process and any children of it. I assume you are trying to have those variables set for the shell that you launch the script from, or globally.

You can add elements to your environment by using

os.environ['LD_LIBRARY_PATH'] = 'my_path'

and run subprocesses in a shell (that uses your os.environ) by using

subprocess.call('sqsub -np ' + var1 + '/homedir/anotherdir/executable', shell=True)

Python Set Environment Variable, Python set environment variable, Python os module environ dictionary, Python You can checkout complete python script and more Python examples from our  To set and get environment variables in Python you can just use the os module: import os # Set environment variables os.environ['API_USER'] = 'username' os.environ['API_PASSWORD'] = 'secret' # Ge

There are many good answers here but you should avoid at all cost to pass untrusted variables to subprocess using shell=True as this is a security risk. The variables can escape to the shell and run arbitrary commands! If you just can't avoid it at least use python3's shlex.quote() to escape the string (if you have multiple space-separated arguments, quote each split instead of the full string).

shell=False is always the default where you pass an argument array.

Now the safe solutions...

Method #1

Change your own process's environment - the new environment will apply to python itself and all subprocesses.

os.environ['LD_LIBRARY_PATH'] = 'my_path'
command = ['sqsub', '-np', var1, '/homedir/anotherdir/executable']
subprocess.check_call(command)
Method #2

Make a copy of the environment and pass is to the childen. You have total control over the children environment and won't affect python's own environment.

myenv = os.environ.copy()
myenv['LD_LIBRARY_PATH'] = 'my_path'
command = ['sqsub', '-np', var1, '/homedir/anotherdir/executable']
subprocess.check_call(command, env=myenv)
Method #3

Unix only: Execute env to set the environment variable. More cumbersome if you have many variables to modify and not portabe, but like #2 you retain full control over python and children environments.

command = ['env', 'LD_LIBRARY_PATH=my_path', 'sqsub', '-np', var1, '/homedir/anotherdir/executable']
subprocess.check_call(command)

Of course if var1 contain multiple space-separated argument they will now be passed as a single argument with spaces. To retain original behavior with shell=True you must compose a command array that contain the splitted string:

command = ['sqsub', '-np'] + var1.split() + ['/homedir/anotherdir/executable']

Making Use of Environment Variables in Python, This means that it's best to use it in cases where having the variable change with the environment is necessary to keep scripts updated. Common  Environment Variables in Python – Read, Print, Set Environment variables is the set of key-value pairs for the current user environment. They are generally set by the operating system and the current user-specific configurations.

Compact solution (provided you don't need other environment variables):

call('sqsub -np {} /homedir/anotherdir/executable'.format(var1).split(),
      env=dict(LD_LIBRARY_PATH=my_path))

Using the env command line tool:

call('env LD_LIBRARY_PATH=my_path sqsub -np {} /homedir/anotherdir/executable'.format(var1).split())

set env variables using python, Hi All, I want to make a python script which will set environment variables. So far, i've been told i can set environment variables in terminal with  A process's environment variables are set when the process is created. Any changes made after this won't affect the process's own copy of the environment variable. This is common to all processes, not just Python. Further, os.environ.data was renamed in Python 3.2 to os.environ._data, the underscore prefix showing that you shouldn't read it directly.

How to Set and Get Environment Variables in Python, To set and get environment variables in Python you can just use the os module: import os # Set environment variables os.environ['API_USER']  My python script which calls many python functions and shell scripts. I want to set a environment variable in Python (main calling function) and all the daughter processes including the shell scripts to see the environmental variable set. I need to set some environmental variables like this: DEBUSSY 1 FSDB 1 1 is a number, not a string. Additionally, how can I read the value stored in an environment variable?

Exporting environment variables from Python to Bash, Have the Python script spit out a set of export XXX="YYY" statements, and use Bash's eval to execute them (at first I got confused, and tried to use  It’s important to remember that the settings you apply in a Python script don’t work outside that specific process; os.environ doesn’t overwrite the environment variables system-wide. If you need to permanently delete or set environment variables you will need to do so with a shell environment, such as Bash.

How to set environment variables in Python, I need to set some environment variables in the python script and I want all the other scripts that are later part of the script) once I set it. The latest installers for Python for Windows can set the System Environment Variable Path automatically if you choose that option during the installation. To verify if this setting is correct, open an administrative command prompt (right-click on the command prompt and choose “ run as administrator ”) and type the word python, then press Enter .

Comments
  • possible duplicate of change current process environment
  • @S.Lott: can you please explain how I can apply that thread to my problem? (cause I do not understand it)
  • @S.Lott (addentum): in particular the excepted answer in that thread starts with "the reason os.environ["LD_LIBRARY_PATH"] does not work" and in my case it works
  • subprocess.check_call(command, env=os.environ) 'module' object has no attribute 'check_call', I'll try using call for now
  • I would avoid a such solution, because it mutates the current process environment. Better pass a copy of it to the child process.
  • the explanation is critical here: visible in this process + all children
  • the first command won't work (you should pass a list, not string here and the wrong environment (sqsub won't be found)). The second command may break if var1 contains shell metacharacters such as '$`!. It is a bad practice to use shell=True if you don't need it e.g., if var1 comes form an external source then the command injection is possible.
  • @J.F.Sebastian thank you for the very valid points. I addressed them in some way. Sure, splitting won't work if one has whitespaces in the path.
  • my comment says nothing about splitting. It is not an appropriate way to fix your answer: it doesn't fix the PATH issue. It introduces other issues. My answer shows how to pass the list correctly.
  • @J.F.Sebastian Right, your comment says nothing about splitting... so what? Mine does, what's wrong with it? That said, both the compact and env-based solutions do work. Give them a try: they address the need for passing LD_LIBRARY_PATH.