$curvalue =~ s/\s/!/g;#Verzweiflungsversch
               
 print "Bau/Raum: '$curvalue' \t ";
               
 if ($curvalue =~ m?^\s*[^/]+\s*/\s*([^/]+)\s*$?) {
               
     $curvalue=$1;
               
     print "getroffen\n";
               
 }

Bau/Raum: 'B4/370'       getroffen
Bau/Raum: 'D40/222' Bau/Raum: ''Bau/Raum: 'B4/369' 

use strict;

my @values = ("B4/370", "", "B4/349", "foo/bar/foo");
foreach my $curvalue (@values) {
    print "Bau/Raum: '$curvalue'\t";
    if ($curvalue =~ m{^\s*[^/]+\s*/\s*([^/]+)\s*$}) {
        $curvalue = $1;
        print "getroffen";
    }
    print "\n";
}