set FLASK_APP via env for portability across shells
set FLASK_APP via env for portability across shells

this does not work on fish (https://fishshell.com):
$ FLASK_APP=hello.py flask run

while this works (hopefully) on any shell:
$ env FLASK_APP=hello.py flask run

fkazimierczak/flask,pallets/flask,pallets/flask,drewja/flask,mitsuhiko/flask,drewja/flask,fkazimierczak/flask,drewja/flask,mitsuhiko/flask,fkazimierczak/flask,pallets/flask