Configuration should be parseable. Unix philosophy has been to use configuration files for anything much more complex than flags, which seems reasonable to me. Don't try to force structured configuration into an arrays of strings.
Traditionally, I see flags as being very application-specific and environment variables being very generic. Environment variables control the behavior of shared libraries and the interaction with the operating system. That separation frees applications from worrying about name collisions between application and library configuration.
The tradeoff Unix made between unstructured configuration (e.g. main(void *arg)) and fully structured configuration was probably wise. Arrays of strings with quoting rules are pretty flexible and human readable. It doesn't gives the full flexibility of the extreme approaches but has aged well.
For example, anyone who is annoyed by environment variables is free to wrap every program they care about in a shell script that sets the environment from the flags they want. Anyone who hates flags can pass environment variables to their version of the script with a bunch of --flag=${MY_PRECIOUS} inside.
Traditionally, I see flags as being very application-specific and environment variables being very generic. Environment variables control the behavior of shared libraries and the interaction with the operating system. That separation frees applications from worrying about name collisions between application and library configuration.
The tradeoff Unix made between unstructured configuration (e.g. main(void *arg)) and fully structured configuration was probably wise. Arrays of strings with quoting rules are pretty flexible and human readable. It doesn't gives the full flexibility of the extreme approaches but has aged well.
For example, anyone who is annoyed by environment variables is free to wrap every program they care about in a shell script that sets the environment from the flags they want. Anyone who hates flags can pass environment variables to their version of the script with a bunch of --flag=${MY_PRECIOUS} inside.