Yes, that's why you need to figure out the actual line number. "123" was just an example. You can determine the line number with l Engine::_Execute ... lines that are breakable will show with a colon (:) after the line number in the debugger. Hence, if you see this:

100 sub Engine::Execute
101 {
102        
103:  foreach (@commands)
104   {
105:    $cmd = $_;
106:    if($cmd =~ /INITIAL/i)
107     {
[download]

... then you would type b 106 $cmd =~ /INITIAL/i

Again, these numbers are just examples. You need to determine the actual line number for yourself with l Engine::_Execute!