A generic configuration files generator

In your application there are many configurations (db host/port/username/password...), and you may save these in some configuration files.

It's a bad practice to check the configuration files into your revision control.

My solution is generating configurations. When generating configurations, only configuration file templates need to be checked into revision control.

Suppose You have 2 configuration files:

• src/main/resources/appname.json
• redis.conf

How could you switch to genconf.lua?

1. Remove those files from revision control, and add them to .gitignore

2. Create templates for appname.json and redis.conf

3. Make a genconf dir in root of your code repo as following and check these files into revision control:

    genconf
      |-appname.json -> configuration template for the app
      |-redis.conf -> configuration template for redis
      |-genconf.conf.lua -> configuration for genconf.lua
   

The content of genconf.conf.lua:

vars = {
	'redis.host',
	'redis.port',
}

templates = {
	{ name = 'appname.json', target = 'src/main/resources/appname.json' },
	{ name = 'redis.conf', target = 'redis.conf' },
}

It defines variables, and target path of templates (i.e. where should genconf save the result).

name is relative to genconf/ dir, and target path is relative to current dir. You MUST use '/' as path separator no matter what OS you are using.

appname.json:

{
	redis: {
		host: "${redis.host}",
		port: ${redis.port}
	}
}

redis.conf:

port ${redis.port}
bind 127.0.0.1

timeout 0
......

In templates, use the bash-like ${name} notation to reference the variable.

The first time you checkout the code into a local dir, run genconf.lua to generate configurations:

lua genconf.lua redis.host=localhost redis.port=6379

And you can also just run:

luajit genconf.lua

If values are not specified in command line, genconf.lua will prompt user to input the value:

$ luajit genconf.lua
redis.host=_

The cursor will be after '=', then you input the value.

After configuration files generated, you can build or run your app.

NOTE: Both lua and luajit are OK, luajit is preferred. I use readline via luajit-ffi when it's available. So with luajit you can do better line editing.

Once you have specified or inputed the value of a variable, genconf.lua will cache it in a file named .genconf.cache.lua.

Next time instead of typing them again, just run:

lua genconf.lua --use-cached

genconf.lua will use the cached values. If there are new variables, you can still specify them in command line:

lua genconf.lua --use-cached "new.var=another test"

NOTE: above example also showed how to deal with values that contains spaces.

And the prompt will also change. For example, if you have used localhost as the values of redis.host:

$ luajit genconf.lua
redis.host=[localhost]_

Then you type Enter, genconf.lua will automatically use localhost as the value of redis.host.

How to clean the cache? Just remove .genconf.cache.lua.

There are two choices:

1. Add genconf.lua to your codebase
2. Install genconf.lua (to for example /usr/bin) on every machine you use genconf.lua

They both have advantages and disadvantages.

1. Add genconf.lua to your codebase: if you want to upgrade it you must make a commit to all your codebases.
2. Install it on machine: your code base depends on an external software.

I recommend 1. for small projects and 2. for larger projects.

• lua

Optional:

• luajit-ffi
• readline

• Auto-detect OS (Linux / Windows)

Variable name can only contains [A-Za-z0-9._-]

• genconf/genconf.conf.lua -> configuration
• .genconf.cache.lua -> cache

Generate what should be added to .gitignore:

lua genconf.lua --gitignore

Use cached values:

lua genconf.lua --use-cached

Get help:

lua genconf.lua --help