Use an environment file


Compose V1 no longer receives updates and will not be available in new releases of Docker Desktop after June 2023.

Compose V2 is included with all currently supported versions of Docker Desktop. For more information, see Migrate to Compose V2.


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 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


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.