my $file = '/path/to/file';
my $line_start = 'BB';
my $search  = 'wort3';

open my $fh,'<',$file or die $!;
while(my $line = <$fh>){
    next unless $line =~ /^\Q$line_start\E/;
    print "yes\n" if $line =~ /\Q$search\E/;
}
close $fh;