c:\@Work\Perl\monks>perl -wMstrict -le
"use 5.014;
 ;;
 my $curdir   = 'Y:\Music\Schubert\Lieder\Terfel';
 my $startdir = 'Y:\mUsIc\\';
 ;;
 my $plsname =
   $curdir =~ s{ \A (?i) \Q$startdir\E | \\ }{ $-[0] ? '_' : '' }xmsreg . '.pls';
 print qq{'$plsname'};
"
'Schubert_Lieder_Terfel.pls'