use File::Spec;
my $src='C:\user\blala';
my $dest='C:\NEWDIR\user\blala';

my $file_src  = 'C:\user\blala\Desktop\map';
my $file_rel  = File::Spec->abs2rel($file_src,$src);
my $file_dest = File::Spec->rel2abs($file_rel,$dest);

print "SRC: $file_src\n";
print "REL: $file_rel\n";
print "DST: $file_dest\n";