# Dev, Staging, Prod: One Config File, No Copy-Paste

![banner](https://articles.aux4.blog/data/posts/aux4/one-config-file-for-every-environment/banner.png)

## Introduction

Dev, staging, and prod settings have a way of sprawling — the same host, port, and database name copy-pasted across a dozen scripts, drifting apart until a deploy points at the wrong database. This post keeps every environment in one `config.yaml` and selects it at runtime with `--config`, so a single command behaves correctly everywhere with no duplication.

## Install the package

```bash
aux4 aux4 pkger install aux4/config
```

## Step 1: one file, one section per environment

Everything lives under a top-level `config:` key, with a named section per environment. Create `config.yaml`:

```yaml
config:
  dev:
    host: localhost
    port: 3000
    database: app_dev
  staging:
    host: staging.internal
    port: 3000
    database: app_staging
  prod:
    host: db.example.com
    port: 5432
    database: app_prod
```

## Step 2: read values

`aux4 config get` reads a whole section as JSON, or a single value by path (nested paths use `/`):

```bash
aux4 config get --file config.yaml dev
```

```json
{ "host": "localhost", "port": 3000, "database": "app_dev" }
```

```bash
aux4 config get --file config.yaml prod/port
```

```text
5432
```

`aux4 config set --file config.yaml --name staging/host --value staging.example.com` writes a value back (creating nested paths as needed).

## Step 3: the payoff — one command, every environment

Here's where it pays off. When a command runs with `--configFile` and `--config`, aux4 loads that section and **auto-fills any command variable whose name matches a key** — no glue code. Create `.aux4`:

```json
{
  "profiles": [
    {
      "name": "main",
      "commands": [
        {
          "name": "connect",
          "execute": [
            "log:connecting to ${database} at ${host}:${port}"
          ],
          "help": {
            "text": "Connect to a database server",
            "variables": [
              {
                "name": "host",
                "text": "The server host"
              },
              {
                "name": "port",
                "text": "The server port"
              },
              {
                "name": "database",
                "text": "The database name"
              }
            ]
          }
        }
      ]
    }
  ]
}
```

The command declares `host`, `port`, and `database` but sets none of them. `--config` picks the section that fills them:

```bash
aux4 connect --configFile config.yaml --config dev
```

```text
connecting to app_dev at localhost:3000
```

```bash
aux4 connect --configFile config.yaml --config prod
```

```text
connecting to app_prod at db.example.com:5432
```

Same command, same variables — the environment is the only thing that changes. There's no `if dev … elif prod` anywhere; `--config prod` simply hands the command prod's values.

## Step 4: shared defaults, defined once

Settings common to every environment shouldn't be repeated three times. Put them in a `defaults.json`:

```json
{ "sslmode": "require", "poolSize": 10 }
```

Then merge them into each section (`config merge` reads JSON on stdin; `--save` writes the result back):

```bash
cat defaults.json | aux4 config merge --file config.yaml --name dev --save
cat defaults.json | aux4 config merge --file config.yaml --name staging --save
cat defaults.json | aux4 config merge --file config.yaml --name prod --save
```

Add `${sslmode}` and `${poolSize}` (with matching variables) to the `connect` command, and every environment now carries the shared defaults on top of its own values:

```bash
aux4 connect --configFile config.yaml --config prod
```

```text
connecting to app_prod at db.example.com:5432 (sslmode=require, pool=10)
```

Change a default once and re-merge — every environment stays in sync.

## Conclusion

`aux4/config` collapses your environment sprawl into one file: sections for dev, staging, and prod, selected with `--config`, feeding a command's variables automatically. No copy-paste, no environment branching, and no more deploys pointed at the wrong database — just one config, everywhere.

## See Also

- [aux4/config](https://hub.aux4.io/r/public/packages/aux4/config)