my $title = "PowerBook_Duo_280";
my @result = split( "/", $title );
my $alttitle = "";
my $alttitle2 = "";
foreach (@result)
{
  $alttitle  = $_;
  $alttitle2 = $_;
  $alttitle  =~ s/PowerBook_//g;
  $alttitle2 =~ s/PowerBook_/PB_/g;
}
print $alttitle  . "\n";
print $alttitle2 . "\n";

# output:
# jotham@leviathan:~$ perl replace.pl
# Duo_280
# PB_Duo_280
# jotham@leviathan:~$