Why can’t environmental variables set in python persist?

by

You can’t do it from python, but some clever bash tricks can do something similar. The basic reasoning is this: environment variables exist in a per-process memory space. When a new process is created with fork() it inherits its parent’s environment variables. When you set an environment variable in your shell (e.g. bash) like this: 

export VAR="foo"

What you’re doing is telling bash to set the variable VAR in its process space to “foo”. When you run a program, bash uses fork() and then exec() to run the program, so anything you run from bash inherits the bash environment variables.

Now, suppose you want to create a bash command that sets some environment variable DATA with content from a file in your current directory called “.data”. First, you need to have a command to get the data out of the file: 

cat .data

That prints the data. Now, we want to create a bash command to set that data in an environment variable: 

export DATA=`cat .data`

That command takes the contents of .data and puts it in the environment variable DATA. Now, if you put that inside an alias command, you have a bash command that sets your environment variable:

alias set-data="export DATA=`cat .data`"

You can put that alias command inside the .bashrc or .bash_profile files in your home directory to have that command available in any new bash shell you start.

More Related Contents:

  1. How to add to the PYTHONPATH in Windows, so it finds my modules/packages?
  2. Saving an Object (Data persistence)
  3. How to set environment variables in Python?
  4. “ImportError: No module named site” on Windows
  5. How to set environment variables in PyCharm?
  6. Python: Platform independent way to modify PATH environment variable
  7. How do I make environment variable changes stick in Python?
  8. How to set env variable in Jupyter notebook
  9. Disable assertions in Python
  10. Securely storing environment variables in GAE with app.yaml
  11. When to use sys.path.append and when modifying %PYTHONPATH% is enough
  12. In Python script, how do I set PYTHONPATH?
  13. Easiest way to persist a data structure to a file in python?
  14. Python: Exporting environment variables in subprocess.Popen(..)
  15. nltk doesn’t add $NLTK_DATA to search path?
  16. Tensorflow set CUDA_VISIBLE_DEVICES within jupyter
  17. Reading and writing environment variables in Python? [duplicate]
  18. What is the use of python-dotenv?
  19. Set LD_LIBRARY_PATH before importing in python
  20. How can I access environment variables in Python?
  21. Launch Pycharm from command line (terminal)
  22. How to add to and remove from system’s environment variable “PATH”?
  23. Environment Variables when script run by cron
  24. How to get the PATH environment-variable separator in Python?
  25. Loading environment modules within a python script
  26. How to access environment secrets from a Github workflow?
  27. Is it possible to set an environment variable from Python permanently?
  28. Bundling Data files with PyInstaller 2.1 and MEIPASS error –onefile
  29. How to store a dictionary on a Django Model?
  30. How to evaluate environment variables into a string in Python?

Leave a Comment