Perl Config File

We can make use of Config::Simple module for this.
This library supports parsing, updating and creating configuration files.

Main Features of Config::Simple are as mentioned below:
1) It allows to read config file in different formats/styles like INI-FILE format and HTML format.
2) It allows to read config file in the form of objects and access the variables from the object.
3) It allows to fetch all the variables at into a hash/hashref using "vars" method.

Let's discuss how can we read/modify/write config files easily in perl as mentioned below :
Reading config file in INI-FILE (ini) style
Reading config file in HTTP-LIKE style
Creating config file in INI style

1) Reading/Updating config file in INI-FILE (ini) style

If the configuration file has different blocks, then this style is very useful
Let's explain with the below mentioned example

db_ini.cfg

[mysql]
host=DBI:mysql:host
login=mysql_user
password=mysql_pass
db_name=test
RaiseError=1
PrintError=1

[oracle]
host=DBI:oracle:host
login=oracle_user
password=oracle_pass
db_name=oracle_db
RaiseError=1
PrintError=1
  

Script

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Config::Simple;

my $cfg = new Config::Simple('db_ini.cfg');

#Get Values from Config File
print "\n MySql DB Name     : " . $cfg->param("mysql.db_name");
print "\n MySql DB Password : " . $cfg->param("mysql.password");

print "\n\n Oracle DB Name     : " . $cfg->param("oracle.db_name");
print "\n Oracle DB Password : " . $cfg->param("oracle.password");
 
#Set/Update Values Config File
$cfg->param("mysql.db_name", "new_mysql_db_name");
$cfg->param("mysql.password", "new_mysql_password");

print "\n\n MySql DB Name     : " . $cfg->param("mysql.db_name");
print "\n MySql DB Password : " . $cfg->param("mysql.password");

$cfg->param("oracle.db_name", "new_orcl_db_name");
$cfg->param("oracle.password", "new_orcl_password");

print "\n\n Oracle DB Name     : " . $cfg->param("oracle.db_name");
print "\n Oracle DB Password : " . $cfg->param("oracle.password");

#Adding a new Variable to Config File
$cfg->param("mysql.new_var", "mysql_adding_variable");

print "\n\n MySql New Var     : " . $cfg->param("mysql.new_var");

$cfg->param("oracle.new_var", "oracle_adding_variable");

print "\n\n Oracle New Var     : " . $cfg->param("oracle.new_var");

print "\n\n Deleting Mysql New Var 'new_var' ... ";
$cfg->delete('mysql.new_var'); # deletes 'new_var' from [mysql] block

print "\n\n Deleting Oracle New Var 'new_var' ... ";
$cfg->delete('oracle.new_var'); # deletes 'new_var' from [oracle] block

#Config Vars
#Config::Simple also supports vars() method, which, depending on the context used, returns all the values either as hash or hashref
my %Config = $cfg->vars();
print "\n\n Config Hash Obj : " . Dumper(\%Config);

my $config_ref = $cfg->vars();
print "\n\n Config Hash Ref : " . Dumper($config_ref);
  

db_ini.cfg Output

 MySql DB Name     : test
 MySql DB Password : mysql_pass

 Oracle DB Name     : oracle_db
 Oracle DB Password : oracle_pass

 MySql DB Name     : new_mysql_db_name
 MySql DB Password : new_mysql_password

 Oracle DB Name     : new_orcl_db_name
 Oracle DB Password : new_orcl_password

 MySql New Var     : mysql_adding_variable

 Oracle New Var     : oracle_adding_variable

 Deleting Mysql New Var 'new_var' ... 
 
 Deleting Oracle New Var 'new_var' ... 
 
 Config Hash Obj : $VAR1 = {
          'mysql.PrintError' => '1',
          'mysql.db_name' => 'new_mysql_db_name',
          'oracle.password' => 'new_orcl_password',
          'oracle.host' => 'DBI:oracle:host',
          'mysql.host' => 'DBI:mysql:host',
          'mysql.password' => 'new_mysql_password',
          'oracle.PrintError' => '1',
          'oracle.login' => 'oracle_user',
          'mysql.RaiseError' => '1',
          'oracle.db_name' => 'new_orcl_db_name',
          'oracle.RaiseError' => '1',
          'mysql.login' => 'mysql_user'
        };


 Config Hash Ref : $VAR1 = {
          'mysql.PrintError' => '1',
          'oracle.password' => 'new_orcl_password',
          'mysql.db_name' => 'new_mysql_db_name',
          'oracle.host' => 'DBI:oracle:host',
          'mysql.host' => 'DBI:mysql:host',
          'oracle.PrintError' => '1',
          'mysql.password' => 'new_mysql_password',
          'oracle.login' => 'oracle_user',
          'mysql.RaiseError' => '1',
          'oracle.db_name' => 'new_orcl_db_name',
          'oracle.RaiseError' => '1',
          'mysql.login' => 'mysql_user'
        };
  

2) Reading/Updating config file in HTTP-LIKE style

When we just key and value pairs, this simple HTTP-Like style works.
Let's explain with the below mentioned example

db_http.cfg

host:'DBI:mysql:host'
login:user
password:secret
db_name:test
RaiseError:1
PrintError:1
  

Script

#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use Config::Simple;

my $cfg = new Config::Simple('db_http.cfg');

#Get Values from Config File
print "\n DB Name     : " . $cfg->param("db_name");
print "\n DB Password : " . $cfg->param("password");
 
#Set/Update Values Config File
$cfg->param("db_name", "new_db_name");
$cfg->param("password", "new_password");

print "\n\n DB Name     : " . $cfg->param("db_name");
print "\n DB Password : " . $cfg->param("password");

#Adding a new Variable to Config File
$cfg->param("new_var", "adding_variable");

print "\n\n New Var     : " . $cfg->param("new_var");

print "\n\n Deleting New Var 'new_var' ... ";
$cfg->delete('new_var'); # deletes 'new_var'

#Config Vars
#Config::Simple also supports vars() method, which, depending on the context used, returns all the values either as hash or hashref
my %Config = $cfg->vars();
print "\n\n Config Hash Obj : " . Dumper(\%Config);

my $config_ref = $cfg->vars();
print "\n\n Config Hash Ref : " . Dumper($config_ref);

db_http.cfg Output

 DB Name     : test
 DB Password : secret

 DB Name     : new_db_name
 DB Password : new_password

 New Var     : adding_variable

 Deleting New Var 'new_var' ... 
 
 Config Hash Obj : $VAR1 = {
          'db_name' => 'new_db_name',
          'password' => 'new_password',
          'RaiseError' => '1',
          'PrintError' => '1',
          'login' => 'user',
          'host' => 'DBI:mysql:host'
        };

 Config Hash Ref : $VAR1 = {
          'db_name' => 'new_db_name',
          'password' => 'new_password',
          'RaiseError' => '1',
          'host' => 'DBI:mysql:host',
          'login' => 'user',
          'PrintError' => '1'
        };
  

3) Creating config file in INI style

Creating a config file is explained as mentioned below.

$cfg = new Config::Simple(syntax=>'ini');
$cfg->write("test.cfg");

Supported "syntax" keywords are "ini", "simple" or "http"

write()
Alternatively, you can pass a name to either write() or save() to indicate the name of the file to create instead of modifying existing configuration file

Since we are trying to create a new config file, we need to pass the file name.

Script

$cfg = new Config::Simple(syntax=>'ini');

$cfg->param("mysql.dsn", "DBI:mysql:db;host=localhost.com");
$cfg->param("mysql.user", "username");
$cfg->param("mysql.pass", 'secret');
$cfg->write("test.cfg");
  

test.cfg Output

[mysql]
dsn:mysql:db;host=localhost.com
user:username
pass:secret