it's an internal routine which is only called by other routines, not from the command loop parser (which is a pretty messed up sequence of reqexes spawning hundreds of lines)

however you can call it directly by yourself

  DB<3> &DB::break_on_filename_line('/tmp/sub.pl',4)

  DB<4> L
/tmp/sub.pl:
 4:        print __FILE__,":",__LINE__; 
   break if (1)
[download]

which poses a problem if the file isn't already loaded.

> I'd still like to be able to use the b filename:line [condition] syntax

you can use the aliasing mechanism to define your own command for "break_on_filename_line" and put it into your .perldb rc-file.