I'd probably use duff's solution, but here's another way to do it:

  my $str = join "_", split m([ /]), "[ABC AB AB12/83]";
  substr($str,  0, 1) = "";
  substr($str, -1, 1) = "";
[download]

Update: here's a [very ugly] way to do it all in one line:

  my $str = substr ${\join "_", split m([ /]), "[ABC AB AB12/83]"},
                   1, -1;
[download]