Does not execute default values, subshells, etc.

if you have a standard .env file:

export USER_EMAIL="${USER_EMAIL:-$(git config --get user.email)}"
export JOB_NAME="${CI_PROJECT_PATH//\//-}"
export UPPER_STAGE=$( echo $CI_ENVIRONMENT_STAGE | awk '{ print toupper(substr($1,1,1)) substr($1,2) }' )
export BUILD_JOB_NAME="Build Job Definition $UPPER_STAGE"

values do not get parsed correctly:

USER_EMAIL=""
JOB_NAME=""
UPPER_STAGE=$( echo $CI_ENVIRONMENT_STAGE | awk '{ print toupper(substr($1,1,1)) substr($1,2) }' )
BUILD_JOB_NAME=Build Job Definition $UPPER_STAGE

See also: https://github.com/theskumar/python-dotenv/issues/326 (1 year ago, no response)
See also: https://github.com/theskumar/python-dotenv/issues/322 (1 year ago, no response)

Happy to open to a PR for this. I think we just need to use python to execute the commands in a shell and set value to the result.

Start by reviewing the documented examples in this issue and the referenced issues #326 and #322, then determine which shell constructs python-dotenv should support. The expected result is correctly resolved default values, substitutions, and command substitutions, but the issue does not name source files or tests; resolve scope and execution safety before implementation.