test
  ->trEE
    ->/A
      ->/b

##</code><code>##

use strict;
use warnings;

# hash for file-system data
my %tree;

#build a datastructure that represents directory tree
#for everything below "/test"
build_tree ("/test", \%tree);

# get realpath of "c:/test/tree/a/b"
my $p = getRealPath ("TREE/A/B", \%tree);

print $p;

sub build_tree
{ 
	my $dir  = shift;
	my $ref  = shift;
	my $dirh = shift;

	opendir $dirh, $dir or die $!;
	
	while ( $_ = readdir ($dirh) )
	{

		next if /^\./;
		next unless -d "$dir/$_";
		
		$ref->{subdirs}->{lc($_)} = { name=>$_, subdirs=>{} };
		
		build_tree ("$dir/$_", $ref->{subdirs}->{lc($_)});
	}
	
	closedir $dirh;
}

sub getRealPath 
{
	my @path = split ("/", shift);
	my $ref  = shift;
	
	my $path = "";
	
	for ( @path )
	{
		$path .= "/" . $ref->{subdirs}->{lc($_)}->{name};
		$ref = $ref->{subdirs}->{lc($_)};
	}
	
	return $path;

}

##</code><code>##

test/trEE/A/B