"default": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": [
        "username/my-app:bar"
      ]
    }
  }
}
```

## Command line

You can also override target configurations from the command line with the
[`--set` flag](/reference/cli/docker/buildx/bake.md#set):

```hcl
# docker-bake.hcl
target "app" {
  args = {
    mybuildarg = "foo"
  }
}
```

```console
$ docker buildx bake --set app.args.mybuildarg=bar --set app.platform=linux/arm64 app --print
```

```json
{
  "group": {
    "default": {
      "targets": ["app"]
    }
  },
  "target": {
    "app": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "args": {
        "mybuildarg": "bar"
      },
      "platforms": ["linux/arm64"]
    }
  }
}
```

Pattern matching syntax defined in [https://golang.org/pkg/path/#Match](https://golang.org/pkg/path/#Match)
is also supported:

```console
$ docker buildx bake --set foo*.args.mybuildarg=value  # overrides build arg for all targets starting with "foo"
$ docker buildx bake --set *.platform=linux/arm64      # overrides platform for all targets
$ docker buildx bake --set foo*.no-cache               # bypass caching only for targets starting with "foo"
```

Complete list of attributes that can be overridden with `--set` are:

- `args`
- `attest`
- `cache-from`
- `cache-to`
- `context`
- `contexts`
- `dockerfile`
- `entitlements`
- `labels`
- `network`
- `no-cache`
- `output`
- `platform`
- `pull`
- `secrets`
- `ssh`
- `tags`
- `target`

## Environment variables

You can also use environment variables to override configurations.

Bake lets you use environment variables to override the value of a `variable`
block. Only `variable` blocks can be overridden with environment variables.
This means you need to define the variables in the bake file and then set the
environment variable with the same name to override it.

The following example shows how you can define a `TAG` variable with a default
value in the Bake file, and override it with an environment variable.

```hcl
variable "TAG" {
  default = "latest"
}

target "default" {
  context = "."
  dockerfile = "Dockerfile"
  tags = ["docker.io/username/webapp:${TAG}"]
}
```

```console
$ export TAG=$(git rev-parse --short HEAD)
$ docker buildx bake --print webapp
```

The `TAG` variable is overridden with the value of the environment variable,
which is the short commit hash generated by `git rev-parse --short HEAD`.

```json
{
  "group": {
    "default": {
      "targets": ["webapp"]
    }
  },
  "target": {
    "webapp": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "tags": ["docker.io/username/webapp:985e9e9"]
    }
  }
}
```

### Type coercion

Overriding non-string variables with environment variables is supported. Values
passed as environment variables are coerced into suitable types first.

The following example defines a `PORT` variable. The `backend` target uses the
`PORT` variable as-is, and the `frontend` target uses the value of `PORT`
incremented by one.

```hcl
variable "PORT" {
  default = 3000
}

group "default" {
  targets = ["backend", "frontend"]
}

target "backend" {
  args = {
    PORT = PORT
  }
}

target "frontend" {
  args = {
    PORT = add(PORT, 1)
  }
}
```

Overriding `PORT` using an environment variable will first coerce the value
into the expected type, an integer, before the expression in the `frontend`
target runs.

```console
$ PORT=7070 docker buildx bake --print
```

```json
{
  "group": {
    "default": {
      "targets": [
        "backend",
        "frontend"
      ]
    }
  },
  "target": {
    "backend": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "args": {
        "PORT": "7070"
      }
    },
    "frontend": {
      "context": ".",
      "dockerfile": "Dockerfile",
      "args": {
        "PORT": "7071"
      }
    }
  }
}
```