Add Read Existing Dot Env File Into Env Vars as a Mise TIL

mise/read-existing-dot-env-file-into-env-vars.md

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+# Read Existing Dot Env File Into Env Vars
+
+Just about any web app that I've worked on has had a `.env` file as a way of
+configuring aspects of the app specific to that environment. These typically
+are read into the environment with a language-specific
+[dotenv](https://github.com/bkeepers/dotenv) tool.
+
+Mise supports this convention. In addition to specifying individual non-secret
+env vars, you can also instruct `mise` to read-in a `.env` file like so:
+
+```toml
+[env]
+PORT=3344
+_.file = ".env"
+```
+
+The `_.file` line tells `mise` that there is a file `.env` with key-value pairs
+that it should read in. It can even handle `.env.json` and `.env.toml` file
+formats.
+
+To ensure that `mise` is picking up the values from the `.env` file, you can
+run the following command and make sure they show up in the output:
+
+```bash
+$ mise env
+```
+
+[source](https://mise.jdx.dev/environments/secrets.html)