a couple of things:
1.When there is an error such as "'env' is not recognized as an internal or external command, operable program or batch file" it means that the system is trying to execute a command named env. This has nothing to do at all with setting up your environment variables.
Env is not a command in windows, but in unix. I understand that you have a windows machine though. What you can do is run "git bash". (You could get it by itself but it comes with Heroku's CLI).
This gives you a unix-like environment where the "env" command is supported, and then you can run the actual heroku pg:pull command.
2.If that still doesn't work, there is a workaround which works,without installing anything extra. Actually this is based on a ticket which I submitted to Heroku so I'm just going to quote their response:
"The pg:push command is just a wrapper around pg_dump
and pg_restore
commands. Due to the bug you encountered, it sounds like we should go ahead and do things manually. Run these using cmd.exe (The Command Prompt application you first reported the bug). First grab the connection string from your heroku application config vars.
heroku config:get DATABASE_URL
Then you want to pick out the username / hostname / databasename parts from the connection string, ie: postgres:// username : password @ hostname : port / databasename. Use those variables in the following command and paste in the password when prompted for one. This will dump the contents of your heroku database for a local file.
pg_dump --verbose -F c -Z 0 -U username -h hostname -p port databasename > heroku.dump
Next you will load this file into your local database. One thing that the CLI does before running this command is to check and make sure the target database is empty, because running this against a database with real data is something you want to avoid so be careful with pg_restore. When running this manually you run the risk of mangling your data without the CLI check, so you may want to manually verify that the target database is empty first.
pg_restore --verbose --no-acl --no-owner -h localhost -p 5432 -d mydb2 < heroku.dump
I am sorry this is not a better experience, I hope this will help you make progress. We are in the process of rewriting our pg commands so that they work better on all platforms including windows, but there is no solid timeline for when this will be completed."