Environment variables¶

Environment variables are now supported in two flavours

Environment variables during command-line integration¶

If an environment variable of the form

CONFIGGLUE_FOO_BAR is defined, it will be used to override the configuration value for option foo in section bar, according to the following precedence rules:

Explicitly defined via command-line (i.e, –section_option=value)
Implicitly defined via environment variable (i.e, CONFIGGLUE_SECTION_OPTION)
Explicitly defined via configuration files
Implicitly defined via schema defaults

To illustrate, a few examples. Given the example from the quickstart guide, the following examples illustrate the precedence rules just mentioned.

Implicitly defined via schema defaults

$ python app.py
foo option has default value: 0
bar option has default value: False

Implicitly defined via environment variable (overriding schema defaults)

$ CONFIGGLUE_FOO=3 python app.py
foo option has been configured with value: 3
bar option has default value: False

Explicitly defined via command-line

$ CONFIGGLUE_FOO=3 python app.py --foo=2
foo option has been configured with value: 2
bar option has default value: False

Explicitly defined via configuration files

$ echo "[__main__]\nfoo = 5" > config.ini
$ python app.py
foo option has been configured with value: 5
bar option has default value: False

Implicitly defined via environment variable (overriding config file)

$ CONFIGGLUE_FOO=33 python app.py
foo option has been configured with value: 33
bar option has default value: False

Environment variables as placeholders in configuration files¶

In the configuration files, if an option has a value such as

$FOO

or

${FOO}

it will be interpolated using the FOO environment variable, or if that variable is not defined, it will fallback to the default value for that option. Alternatively, you can specific a default using bash-like syntax

${FOO:-default}

Using the same example as shown in the quickstart guide, this use case can be illustrated as follows.

Specifying a value in the configuration file using an environment variable

$ echo "[__main__]\nfoo = \$BAZ" > config.ini
$ BAZ=33 python app.py
foo option has been configured with value: 33

If the environment variable is not defined, fallback to the default value

$ python app.py
foo option has default value: 0

If the environment variable is not defined, use the specified default

$ echo "[__main__]\nfoo = \${BAZ:-bar}" > config.ini
$ BAZ=33 python app.py
foo option has been configured with value: 33
$ python app.py
foo option has been configured with value: bar