To get the value of an environment variable:
(System/getenv "HOME") ;=> "/home/you"
You can set environment variables on your system in the usual way (in ~/.profile with
export FOO=something), or you can set it just for one run:
$ FOO=42 lein run
or, after creating an uberjar of your app:
$ FOO=42 java -jar my-app-0.1.0-standalone.jar