[vertex-four]

> plain old unix-style config files

Like what? /etc/X11/xorg.conf is a different format from /etc/openldap/ldap.conf is a different format from /etc/crontab is a different format from /etc/nsswitch.conf.

Unifying configuration files under a single common format would allow for less complexity in configuration management tools - you could just create a data structure and serialise it to a file, rather than dealing with text-based templates with countless edge cases.

[thwarted]

And yet elsewhere, domain specific languages are preferred.

I'd love to see the One Config File Format To End Config File Formats that supports xorg, ldap, crontab, nsswitch, apache, and anything else. Sure, use something like JSON, XML, INI, or YAML for this, for which the format is regular and parsable with an off-the-shelf parser, but then the domain specific stuff just moves into, for example, the key names. You've gained nothing in terms of maintenance or automatic editablity, but you have gained consistent use of whitespace and punctuation characters.

"Creating a data structure and serializing it to a file" is doable text-based formats. Admittedly, templates are troublesome, but that's because you shouldn't be using templates anyway. Templates are an attempt to avoid understanding the domain specific language but still maintain the power of the domain specific language. I've never had good luck with this, which is why I mainly use configuration management tools, like puppet, to keep a fleet of machines in a consistent state by putting fully formed files in place. Templating takes significant care.

[vertex-four]

> And yet elsewhere, domain specific languages are preferred.

Yes, but that's because the DSLs actually provide something of value. Having umpteen different ways to store a list of values under a key, for example, doesn't solve anything.

> the domain specific stuff just moves into, for example, the key names

Anything that wants to manage the system already needs to know the key names, etc - implementing a single config file format is significantly reducing complexity because they no longer have to implement config file parsers/serialisers.

> I mainly use configuration management tools, like puppet, to keep a fleet of machines in a consistent state by putting fully formed files in place

These tools are currently primarily based on templating. If you ever have reason to write your own resources for them (if you have to edit a config file for something obscure or in-house), you're going to have to write a text-based template to convert from your nice Puppet data structure to the config file format - and probably get it wrong on edge cases.