If you have a text file with key/value pairs like:
API=http://localhost:8080
USERNAME=my-username
and want to export them into the shell environment, you can do so with:
export $(cat .env | xargs)The contents of .env are piped into xargs which constructs a single-line string where the key/value pairs are separated by a whitespace. export then exports these key/value pairs as variables into the shell environment.
This is usually good enough for me, but if you want to account for comments and other special cases, here is a nice answer on StackOverflow.