Jekyll

[build]
  command = "bundle exec jekyll build --trace"
  publish = "_site"

[build.environment]
  JEKYLL_ENV = "production"

You can just run jekyll build if you want - Netlify will still use bundle either way.

I like to use a Makefile with a build command set up, including the prod environment setting there. Then if I change the Makefile, I get the same change in both my local usage and remote builds.

[build]
  command = "make build"
  publish = "_site"