mirror of https://github.com/docker/docs.git
59 lines
2.5 KiB
Markdown
59 lines
2.5 KiB
Markdown
---
|
|
description: Declare default environment variables in a file
|
|
keywords: fig, composition, compose, docker, orchestration, environment, env file
|
|
title: Use an environment file
|
|
redirect_from:
|
|
- /compose/env-file/
|
|
---
|
|
{% include compose-eol.md %}
|
|
|
|
## Syntax
|
|
The following syntax rules apply to environment files:
|
|
|
|
- Lines beginning with `#` are processed as comments and ignored.
|
|
- Blank lines are ignored.
|
|
- Unquoted and double-quoted (`"`) values have [parameter expansion](#parameter-expansion) applied.
|
|
- Each line represents a key-value pair. Values can optionally be quoted.
|
|
- `VAR=VAL` -> `VAL`
|
|
- `VAR="VAL"` -> `VAL`
|
|
- `VAR='VAL'` -> `VAL`
|
|
- Inline comments for unquoted values must be preceded with a space.
|
|
- `VAR=VAL # comment` -> `VAL`
|
|
- `VAR=VAL# not a comment` -> `VAL# not a comment`
|
|
- Inline comments for quoted values must follow the closing quote.
|
|
- `VAR="VAL # not a comment"` -> `VAL # not a comment`
|
|
- `VAR="VAL" # comment` -> `VAL`
|
|
- Single-quoted (`'`) values are used literally.
|
|
- `VAR='$OTHER'` -> `$OTHER`
|
|
- `VAR='${OTHER}'` -> `${OTHER}`
|
|
- Quotes can be escaped with `\`.
|
|
- `VAR='Let\'s go!'` -> `Let's go!`
|
|
- `VAR="{\"hello\": \"json\"}"` -> `{"hello": "json"}`
|
|
- Common shell escape sequences including `\n`, `\r`, `\t`, and `\\` are supported in double-quoted values.
|
|
- `VAR="some\tvalue"` -> `some value`
|
|
- `VAR='some\tvalue'` -> `some\tvalue`
|
|
- `VAR=some\tvalue` -> `some\tvalue`
|
|
|
|
### Parameter Expansion
|
|
Compose supports parameter expansion in environment files.
|
|
Parameter expansion is applied for unquoted and double-quoted values.
|
|
Both braced (`${VAR}`) and unbraced (`$VAR`) expressions are supported.
|
|
|
|
For braced expressions, the following formats are supported:
|
|
- Direct substitution
|
|
- `${VAR}` -> value of `VAR`
|
|
- Default value
|
|
- `${VAR:-default}` -> value of `VAR` if set and non-empty, otherwise `default`
|
|
- `${VAR-default}` -> value of `VAR` if set, otherwise `default`
|
|
- Required value
|
|
- `${VAR:?error}` -> value of `VAR` if set and non-empty, otherwise exit with error
|
|
- `${VAR?error}` -> value of `VAR` if set, otherwise exit with error
|
|
- Alternative value
|
|
- `${VAR:+replacement}` -> `replacement` if `VAR` is set and non-empty, otherwise empty
|
|
- `${VAR+replacement}` -> `replacement` if `VAR` is set, otherwise empty
|
|
|
|
## Precedence
|
|
|
|
Environment variables from an environment file have lower precedence than those passed via the command-line or via the `environment` attribute in the `docker-compose.yml` file.
|
|
For more information, see [Environment variables precedence](envvars-precedence.md).
|