The INI file format is a simple file format that allows 2-level configuration options. It was extensively used in MS DOS and MS Windows, and it can be used in lots of places as it is very simple.

examples/config.ini

[openweathermap]
api = asdahkaky131

[aws]
api_key = myaws7980
api_code = qkhdkadyday

[digital_ocean]
api = seaworld

This format consists of section names (in square brackets) and in each section key-value pairs separated by and = sign and padded by spaces.

There are several articles showing how to read them using plain Perl for example processing config file and the exercise parse INI file however there are several modules on CPAN that would do the work for you in a more generic way.

We'll use Config::Tiny

examples/read_config.pl

use strict;
use warnings;
use 5.010;

use Config::Tiny;
use Data::Dumper qw(Dumper);

my $filename = shift or die "Usage: $0 FILENAME\n";

my $config = Config::Tiny->read( $filename, 'utf8' );

say $config->{digital_ocean}{api};     # seaworld

say $config->{openweathermap}{api};    # asdahkaky131

say $config->{aws}{api_key};           # myaws7980
say $config->{aws}{api_code};          # qkhdkadyday


print Dumper $config;

The line that reads and parses the configuration file is Config::Tiny->read.

It returns a reference to a 2-dimensional hash. The main hash has the sections as keys and the values are the hashes representing each individual section.

We can then access the specific values using the $config->{section}{key} construct.

If we use Data::Dumper we can see the whole data structure: 

$VAR1 = bless( {
                 'digital_ocean' => {
                                      'api' => 'seaworld'
                                    },
                 'openweathermap' => {
                                       'api' => 'asdahkaky131'
                                     },
                 'aws' => {
                            'api_code' => 'qkhdkadyday',
                            'api_key' => 'myaws7980'
                          }
               }, 'Config::Tiny' );

Write config file

Config::Tiny can also write config files and it can also handle key-value pairs without any section. Check the documentation for details.