Might looks like a basic stuff, but I am confused.

How can I maintain the environmental variables(.env) in Laravel or any environment. ?

For example, DB credentials might varies for different environment. 

As of now, all the deployment process are progressing in Jenkins or any deployment tools, it would be good to automate the process
of moving the environmental variables to the specific server.

I think, In earlier days, env variables are modified directly in the server by getting into the SSH or any Connection type.
It would create many confusion on many situations.
Here are my questions,

1. How can we maintain the environmental variables ? (May be git or any versioning system)
2. How can we move the environmental file from Jenkins server to Application server ?
3. How could docker like tools will be helpful here ?