personally, I think a better question is not "whats the best way to parse config files" but "How can I make my config file better for parsing?". Yes it might be taking a longer route (as in thought process wise) but can be truly helpful in the future.

The way I always go about thinking about making a config file is saying to myself "how can I get this all in a hash?" hehe yeah it might not be good to think that way, but its how _I_ think.

When I want to make an easily understood, easily extendable, strong config file, I make use of label's, static information, and alternatives. Ok so that doesnt make much sense...Lets put it this way:

Label:<variable-label>
Static-Info-1:<variable-label>: <some-info-1>
Static-Info-2:<variable-label>: <some-info-2>
Alternative:<variable-label>: Static-alt-Info-1 <static-alt-info-1>
Alternative:<variable-label>: Static-alt-Info-2 <static-alt-info-2>
[download]

So basically label becomes my holder for each static and alternative setting in my config file, so I can refer back to it at a future point in time with my program. In essence even the Label: part is a static peice of information.. To show how this teknique can acctually minimize parsing to almost nothing, I will give a small example:

# Sample Config File
Label:perl-monks:perl-monks
Hostname:perl-monks:www.perlmonks.org
Description:perl-monks:The Perl Monks Webpage
Alt:perl-monks:MonkVar-1 SomeSubVar-1 SomeVar-1-value
Alt:perl-monks:MonkVar-2 SomeSubVar-2 SomeVar-2-value
 
Label:ackers:ackers
Hostname:ackers:www.ackers.net
Description:ackers:Just my Page
Alt:ackers:AckVar-1 SomeSubVar-1 SomeVar-1-value
Alt:ackers:AckVar-2 SomeSubVar-2 SomeVar-2-value
[download]

and the perl code to read that

#!/usr/bin/perl


# Here I will define all the static parts of the config file in an arr
+ay
# this is a nessesity, not only for easily adding features to your con
+fig
# but to keep code changes down to a minimum :)
   
my @carray = ("Label", "Hostname", "Description");

# pretend config.conf holds the information above hehe.
open (CONF, "config.conf");

while (<CONF>) {
 s/\s+$//g;            # remove whitespaces
 s/\s/ /g;             # replace whitespace by space
 next if /^\s*\#/;     # ignore comment lines
 s/\s*\#$//g;          # ignore trailing comments
 next if /^\s*$/;      # ignore empty lines  

 ($one,$two,$three) = split(/:/);
 if ($one eq "Alt") {

  $alt = $one;
  $label = $two;
  $var = $three;


  foreach($three) {
   $$alt{$var} = "$label";
  }
 }
 else {
  foreach ($one) {
   $$one{$two} = "$three";
  }
 }
}  

foreach $thing (keys %Label) {
 foreach $heh (@carray) {
  while ( ($k,$v) = each %$heh ) {
   print "Static Setting: $heh: $v\n" if ($k eq $thing);
  }
 }
 while ( ($k,$v) = each %Alt ) {
  print "Alternate Setting: $k\n" if ($v eq $thing);
 }
 print "\n";
}
[download]

the Alt:whatever:vars thing is there becuase you can take the third part of that and make it into another hash..

but I probably sound pretty stupid all the way through this...I guess Im just trying to give examples of easy extensibility in configuration.