How to update an existing Conda environment with a .yml file

Question

How can a pre-existing conda environment be updated with another .yml file. This is extremely helpful when working on projects that have multiple requirement files, i.e.

Answer 1

alkamid's answer is on the right lines, but I have found that Conda fails to install new dependencies if the environment is already active. Deactivating the environment first resolves this:

source deactivate;
conda env update -f whatever.yml;
source activate my_environment_name; # Must be AFTER the conda env update line!

Answer 2

The suggested answer is partially correct. You'll need to add the --prune option to also uninstall packages that were removed from the environment.yml. Correct command:

conda env update -f local.yml --prune

Answer 3

Try using conda env update:

conda activate myenv
conda env update --file local.yml

Or without the need to activate the environment (thanks @NumesSanguis):

conda env update --name myenv --file local.yml