What is the Unix way for a console script to use config files? - unix

Question

Let's imagine we have some script 'm12' (I've just invented this name) that runs
on Linux computers. If it is situated in your $PATH, you can easily run it
from the console like this:
m12
It will work with the default parameters. But you can customize the work of
this script by running it something like:
m12 --enable_feature --select=3
It is great and it will work. But I want to create a config file ~/.m12rc so I
will not need to specify --enable_feature --select=3 every time I run it.
It can be easily done.
The difficult part is starting here.
So, I have ~/.m12rc config file, but I what to start m12 without parameters that
are stored in that config file. What is the Unix way to do this? Should I run
script like this:
m12 --ignore_config
or there is better solution?
Next. Let's imagine I have a config file ~/.m12rc and I want some parameters from that
file, but want to change them a bit. How should I run the script and how the
script should work?
And the last question. Is it a good idea for script to first look for .m12rc
in the current directory, then in ~/ and then in /etc?
I'm asking all these questions because I what to implement config files in my
small script and I want to make the correct decisions about the design.

Answer 1

The book 'The Art of Unix Programming' by E S Raymond discusses such issues.
You can override the config file with --config-file=/dev/null.
You would normally use the order:
System-wide configuration (/etc/m12/m12rc, or just /etc/m12).
User's personal configuration (~/.m12rc)
Local directory configuration (./.m12rc)
Command-line options
with each later-listed item overriding earlier listed items. You should be able to specify the configuration file to read on the command line; arguably, that should be given precedence over other options. Think about --no-system-config or --no-user-config or --no-local-config. Many scripts do not warrant a system config file. Most scripts I've developed would not use both local config and user config. But that's the way my mind works.
The way I package standard options is to have a script in $HOME/bin (say m12a) that does it for me:
#!/bin/sh
exec m12 --enable_feature --select=3 "$#"
If I want those options, I run m12a. If I want some other options, I run raw m12 with the requisite options. I have multiple hundreds of files in my personal bin directory (about 500 on my main machine, a Mac; some of those are executables, but many are scripts).

Answer 2

Let me share my experience. I normally source config file at the beginning of the script. In the config file I also handle all the parameter switches:
DEFAULT_USER=blabla
while getopts ":u" do
case $opt in
u)
export APP_USER=$OPTARG
;;
esac
done
export APP_USER=${APP_USER-$DEFAULT_USER}
Then within the script I just use variables, this let me to have number of script having same input parameters.
In your case I imaging you would move "getopts" section to script and after it source the config file (if there was no switch to skip sourcing).
You should not put yours script config file to etc, it will require root privilidge to do that, and you simple can live with config file in home.
If you would like anyway to put your script for sharing with other users, it should go to /usr/share...
Another solution use thor (ruby gem), its way simpler to handle input parameter, avoiding work to get same result in bash e.g. getopts support only single letter switches.