---
description: Compose CLI reference
keywords: fig, composition, compose, docker, orchestration, cli, reference
redirect_from:
- /compose/env
title: Link environment variables (superseded)
notoc: true
---

> **Note**: Environment variables are no longer the recommended method for connecting to linked services. Instead, you should use the link name (by default, the name of the linked service) as the hostname to connect to. See the [docker-compose.yml documentation](compose-file.md#links) for details.
>
> Environment variables are only populated if you're using the [legacy version 1 Compose file format](compose-file.md#versioning).

Compose uses [Docker links](/engine/userguide/networking/default_network/dockerlinks.md)
to expose services' containers to one another. Each linked container injects a set of
environment variables, each of which begins with the uppercase name of the container.

To see what environment variables are available to a service, run `docker-compose run SERVICE env`.

<b><i>name</i>\_PORT</b><br>
Full URL, such as `DB_PORT=tcp://172.17.0.5:5432`

<b><i>name</i>\_PORT\_<i>num</i>\_<i>protocol</i></b><br>
Full URL, such as `DB_PORT_5432_TCP=tcp://172.17.0.5:5432`

<b><i>name</i>\_PORT\_<i>num</i>\_<i>protocol</i>\_ADDR</b><br>
Container's IP address, such as `DB_PORT_5432_TCP_ADDR=172.17.0.5`

<b><i>name</i>\_PORT\_<i>num</i>\_<i>protocol</i>\_PORT</b><br>
Exposed port number, such as `DB_PORT_5432_TCP_PORT=5432`

<b><i>name</i>\_PORT\_<i>num</i>\_<i>protocol</i>\_PROTO</b><br>
Protocol (tcp or udp), such as `DB_PORT_5432_TCP_PROTO=tcp`

<b><i>name</i>\_NAME</b><br>
Fully qualified container name, such as `DB_1_NAME=/myapp_web_1/myapp_db_1`

## Related information

- [User guide](index.md)
- [Installing Compose](install.md)
- [Command line reference](./reference/index.md)
- [Compose file reference](compose-file.md)