Append to an environment variable without overwriting values from .env file

Question

Assuming the .env file is loaded before execution, how can you append to it without overriding it?

DEBUG=True
FOO=BAR
PYTHONPATH="/Users/James/project/"

The above file would (?) override it, and that would be bad. I could put it in .bash_profile or .profile, but that's not consistent with what I have now, and I only want to set it for the current virtualenv too.

I don't think this makes any difference, but I'm using Mac OS X (the tutorial I was using was multi-platform)

Solution

What you most likely want to do is export the variables you are interested in. The following will make the variable available to the current shell and any sub-processes it creates:

export PYTHONPATH=$PYTHONPATH:/Users/James/project

Here a process that uses PYTHONPATH will first search the existing path for its target and if not found, try the /Users/James/project. If you wanted to overide some existing path, you could add the new path first:

export PYTHONPATH=/Users/James/project:$PYTHONPATH

In either case, other shells will not see the variable (and obviously closing the shell will make the variable unaccessible).

Comments

[Jonathan Roberts]

What are you trying to do? You want to add a couple environment variables temporarily? It sounds like you just want to export DEBUG=True. This will set the DEBUG variable only for the current shell and it's children.

[noɥʇʎԀʎzɐɹƆ]

@user1794469 Is that possible in the .env file? I want to append to PYTHONPATH.

[Jonathan Roberts]

It shoudl, you just add the current: export PYTHONPATH=$PYTHONPATH:/Users/James/project or export PYTHONPATH=/Users/James/project:$PYTHONPATH depending on which path you want search first.