Enable environment variable substitution in configuration files using
${VAR} syntax. Supports 12-factor app deployment patterns without
hardcoding secrets or environment-specific values.
Syntax:
- Only ${VAR} with curly braces (avoids conflict with $variable system)
- Missing variables preserved as-is (${MISSING} stays unchanged)
- Multiple variables per line supported
- Adjacent variables ${A}${B} handled correctly
Integration:
- Applied in config.Load() after os.ReadFile, before yaml.Unmarshal
- Applied in processIncludes() for each included file
- 12 unit tests covering single/multiple/missing/empty variables
xfy
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