Question

I’m building a script that utilizes a config file (YAML) to read in all the necessary configuration information, then prints out all the necessary steps a Linux Admin needs to step through to build a server.

A required option is for the Linux Admin that’s running the script to be able to override any of the item/value pairs from the config file, at the command-line.

The way I’m currently handling this seems overly cumbersome and I know there’s got to be a more innovative and less clunky way to do this.

---

In the code I:

1. Parse the YAML config file with YAML::Tiny

   location:
       continent: na
       country: us
       city: rh
   

2. Create variables with the same names as the config file items, assigning the values from the config file.

   my $yaml = YAML::Tiny->new;
   $yaml = YAML::Tiny->read($config_yml);
   my $continent = $yaml->[0]->{location}->{continent};
   my $country = $yaml->[0]->{location}->{country};
   my $city = $yaml->[0]->{location}->{city};
   

3. Use Getopt::Long and assign the variables, overriding anything passed at the command-line.

   GetOptions (
       "city=s" => \$city,
       "continent=s" => \$continent,
       "country=s" => \$country,
   );
   

So those are just 3 item/values pairs, my actual config has over 40 and will change…Which makes for a bit of work to have to keep updating. Any suggestions?

Answer 1

You can let the admin override the YAML settings with a single, flexible switch similar to what ssh(1) does with -o. This is especially appropriate if the config settings are numerous and likely to change.

$ myscript -o location:city=rh --option location:country=us

Now, inside the script, you might keep all your runtime config bundled together in a hash for convenience (rather than having $this_and_that_opt scalars proliferate over time). Option parsing would then look something like this:

# First, set up %GlobalAppCfg from defaults and YAML
# now handle "-o location:country=us"
GetOptions('option|o=s' => sub {
                              my (undef, $optstring) = @_;

                              my ($userkey, $val) = split('=', $optstring, 2);
                              my ($major, $minor) = split(':', $userkey,   2);

                              $GlobalAppCfg->{$major}->{$minor} = $val;
                            },
            ...);

or whatever. You can normalize config keys and values, handle arbitrarily deep key/subkey/subkey configs, etc. This can get slippery, so you might like to key-lock that global hash.