DB<1> $curdir = 'Y:\Music\Schubert\Lieder\Terfel';

  DB<2> $startdir = 'Y:\Music';

  DB<3> $curdir =~ s/^\Q$startdir\E\\//i;

  DB<4> $out = join "_", split /\\/, "$curdir.pls";

  DB<5> p $out;
Schubert_Lieder_Terfel.pls