Use YAML! YAML is a simple, human-readable data-serialization format. It can round-trip any Perl data structure (that anything else can parse, anyway -- nothing's perfect) with no loss, doesn't require evals, and is very easy to work with.

One thing YAML's implementors had in mind at the start was to make a better syntax for config files. YAML's brutally simple in this regard:

# snippet
my $data = "anything you want";
DumpFile( "/path/to/file", $data );
my $newdata = LoadFile( "/path/to/file" );
# now $data == $newdata
[download]

The code below is long, but that's mostly data. It dumps the data twice with Data::Dumper, before and after a YAML read/write cycle, just to prove they're the same. Lastly is the data as represented by YAML - very clean and easy to read.

#!/usr/bin/perl
use strict;
use warnings;

use YAML qw/ LoadFile DumpFile Dump /;
use Data::Dumper;
local $Data::Dumper::Indent = 1;
use constant DIV => '-' x 20 . "\n";

my $routers = {
  'routers' => {
    'router1' => '192.168.1.2',
    'router2' => '192.168.1.3',
    'router3' => '192.168.1.4',
    'router4' => '192.168.1.5',
    'router5' => '192.168.1.6',
  }
};
my $groups = {
  'groups' => {
    'group1' => [
      'router1',
      'router5',
    ],
    'group2' => [
      'router1',
      'router2',
      'router3',
    ],
    'group3' => [
      'router2',
      'router3',
      'router4',
    ]
  }
};

print "Dumping initial data...\n" . DIV;
print Dumper $routers, $groups;

print "Writing YAML file...\n";
DumpFile( "./yaml-test.conf", $routers, $groups );

print "Reading YAML file...\n";
( $routers, $groups ) = LoadFile( "yaml-test.conf" );

print "Dumping YAML'd data...\n" . DIV;
print Dumper $routers, $groups;

print "Dumping YAML'd data with YAML...\n" . DIV;
print Dump $routers, $groups;
[download]

Dumping initial data...
--------------------
$VAR1 = {
  'routers' => {
    'router5' => '192.168.1.6',
    'router1' => '192.168.1.2',
    'router3' => '192.168.1.4',
    'router4' => '192.168.1.5',
    'router2' => '192.168.1.3'
  }
};
$VAR2 = {
  'groups' => {
    'group2' => [
      'router1',
      'router2',
      'router3'
    ],
    'group1' => [
      'router1',
      'router5'
    ],
    'group3' => [
      'router2',
      'router3',
      'router4'
    ]
  }
};
Writing YAML file...
Reading YAML file...
Dumping YAML'd data...
--------------------
$VAR1 = {
  'routers' => {
    'router5' => '192.168.1.6',
    'router1' => '192.168.1.2',
    'router3' => '192.168.1.4',
    'router4' => '192.168.1.5',
    'router2' => '192.168.1.3'
  }
};
$VAR2 = {
  'groups' => {
    'group2' => [
      'router1',
      'router2',
      'router3'
    ],
    'group1' => [
      'router1',
      'router5'
    ],
    'group3' => [
      'router2',
      'router3',
      'router4'
    ]
  }
};
Dumping YAML'd data with YAML...
--------------------
--- #YAML:1.0
routers:
  router1: 192.168.1.2
  router2: 192.168.1.3
  router3: 192.168.1.4
  router4: 192.168.1.5
  router5: 192.168.1.6
--- #YAML:1.0
groups:
  group1:
    - router1
    - router5
  group2:
    - router1
    - router2
    - router3
  group3:
    - router2
    - router3
    - router4
[download]