support passing multiple env files

[cmatKhan]

Is your feature request related to a problem? Please describe.

I would like to be able to pass environmental variables that are stored in separate files, eg:

            singularity exec --bind .:/app \
                             --env-file ./.envs/.local/.django \
                             --env-file ./.envs/.local/.postgres \
                             --env-file ./.envs/.local/.regulatory_data \
                             $django_sif bash -c 'cd /app && /start'

Describe the solution you'd like

The environmental variables from each file should be set in the container environment, with later files taking priority

Describe alternatives you've considered

Keeping the environmental variables in separate files can be useful, but of course this can be concatenated and provided to --env-file as it is currently implemented

[dtrudg]

Hi @cmatKhan - this seems like it'd be a useful feature.

If you or anyone else would be interested in contributing a PR to implement it then I don't see any reason why it could not be merged.

Otherwise we'll keep it on the list of suggested features for future development, which we evaluate periodically.