Hi Mauricio,
Thanks for formulating your question so clearly, especially for providing an example. Browsing the forum, one would find how many times I have asked for clarifications so I can understand what a question is about, exactly.
Okay, now back to your question.
Ideally, I could have provided a -q option (for quiet, or something similar) so the output message can be suppressed. As current is with 3DNA, however, the diagnostic information is directed to stderr. This should not be a problem in real life, with the help of Unix/Linux file redirection.
Again, an example would make the point clear. So let's use 'bdl084.pdb', you need to do the following:
find_pair bdl084.pdb bp_info 2> msg1
analyze bp_info 2> msg2
# or by combining them as this
find_pair bdl084.pdb stdout 2> msg1 | analyze 2> msg2
Note I am using bash shell. For other shells, you may need to use something different. Of course, you could also play with some variants along the line.
HTH,
Xiang-Jun