Taming Configuration Files - Example deployment

Overview

Over the past few weeks, this blog has been on building configuration file checking into the application.  The strategy has been to make a tool that checks the configuration file matches a grammar and to build a way to automate this process with make.  The past two posts have been on matching the grammar, and building the script respectively.

This post builds a simple example which shows this system in use.  A helloworld type program which reads name from a configuration file.

The test

The configuration file hello.conf contains the entry:

{name,"Tony"}.

The checker will confirm that this matches the datadef stored in hello_conf.def which contains:

{property_list,[{reqd,name,{list,{builtin,is_integer}}}]}.

Although it is true that the definition is longer than the data it describes, the definition of a configuration file is an application development activity, not an operational matter.  It is conceivable that definitions will be provided in a machine readable (rather than human readable) form.  Note that in Erlang a string is a list of integers.

The program that reads this configuration file, hello.erl is:

-module (hello).

-export([main/1]).

main(_) ->

    Name = get_name(),

    io:format("Hello ~s~n",[Name]).

get_name() ->

    {ok,Bin} = file:read_file("hello.conf.etf"),

    PL = binary_to_term(Bin),

    proplists:get_value(name,PL).

So this program produces the string "Hello Tony". This program reads the compiled configuration file hello.conf.etf which is produced by the config_check program we built last blog post.

Finally the compilation and test is run by make.  Here is the Makefile:

test: hello.conf.etf ebin/hello.beam

escript ebin/hello.beam

hello.conf.etf:hello_conf.def hello.conf

./config_check hello.conf hello_conf.def

ebin/hello.beam: src/hello.erl

erlc -o ebin src/hello.erl

clean:

rm hello.conf.etf ebin/hello.beam

To run the test type make from the terminal prompt.  To run with a different name, simply edit hello.conf and type make again.