Your variable names are very confusing. You're looking for $old_name in file $new?? In fact, I think you confused yourself. Use consistent, meaningful names.

Is this what you want?

sub fc {
   # Pass by reference for efficiency.
   local $_; *_ = \$_[1];
   return uc(substr($_, 0, 1)) . lc(substr($_, 1));
}


sub match_case {
   # Very simplistic.
   # Pass by reference for efficiency.
   our $template; *template = \$_[0];
   our $s;        *s        = \$_[1];

   return uc($s) if (uc($template) eq $template);

   my $first_char = substr($template, 0, 1);
   return fc($s) if (uc($first_char) eq $first_char);

   return lc($s);
}


sub wanted {
    if ((-f $File::Find::name) && ($File::Find::name !~ m/\.bak/)) {
        my $old_file_name = $File::Find::name;

        (my $new_file_name = $old_file_name) =~ s/$old_name/$mname/;

        # # Make backup
        # rename($new_file_name, $new_file_name.'.bak');

        local *IN;
        open(IN, '<' . $old_file_name)
        or die("Unable to open old file: $!$/");

        local *OUT;
        open(OUT, '>' . $new_file_name)
        or die("Unable to create new file: $!$/");

        while (<IN>) {
            s/($old_name)/match_case($1, $mname)/eig;
            print OUT $_;
        }

        close(OUT);
        close(IN);

        unlink($old_file_name);
    }
}
[download]

Update: Added match_case.

Update: Added unlink as per later discussions.

Ok so the only thing I am missing here is that I do no want to make a backup of the old file all I want to do is rename the old to the new then open the new for writing and make the switches in the new file.
SUNADMN
USE PERL

Yes this is exactly correct thank you much for fixing my problem.
SUNADMN
USE PERL