gcfgenv

gcfgenv is a Go package for configuring applications with environment variables in addition to their existing configuration files.

The precise goal is to provide environment variable overrides for gcfg configurations without the need to specify anything manually whatsoever. There is a strong "convention over configuration" ethos.

gcfgenv is not a general-purpose way to read environment variables into a struct -- the package only supports to structures and conventions permitted by gcfg, which are comparatively limited.

Usage

There are only two exported functions:

• ReadWithEnvInto(), which wraps gcfg.ReadInto(); and
• ReadFileWithEnvInto(), which wraps gcfg.ReadFileInto()

Configuration fields are converted to environment variables using the follow rules:

• Section and field names (including those using the gcfg struct tag) are converted to uppercase.
• Slice fields use , as a separator.
• Slice fields are appended to rather than replaced (as with the original gcfg package).
• Dashes are converted to underscores.
• Subsection names are left as-is.

For example, the following environment variables (and global prefix APPNAME_):

APPNAME_SEC_FIELD=geese
APPNAME_SEC_k1_FIELD=cats
APPNAME_SEC_k1_OTHER_FIELD=zebras,elephants

are equivalent to the following configuration file:

[sec]
field = geese

[sec "k1"]
field = cats
other-field = zebras
other-field = elephants

Limitations

• Slice fields that may legitimately contain , in their entries cannot be parsed correctly.

• No support for setting gcfg's "default values" subsection. It is not possible to determine after the initial configuration file pass whether a value was defaulted, so resetting a field's default via environment variable could lead to surprising results.

• Modifying subsections with whitespace in the heading (i.e. [Section "Sub Section"]) requires using environment variables with whitespace, since any form of automatic substitution (with e.g. _ or -) would lead to ambiguity. However, most shells and other tools do not handle whitespace in environment variables well, so we recommend using snake_case or kebab-case in subsection headings instead.

Versioning

gcfgenv follows semantic versioning.

License

Licensed under the Apache License, Version 2.0. See LICENSE for details.