Parsing Output of mDNS, AppleScript Studio

[MattPat]

My program is looking for computers that have Remote Apple Events enabled. It's possible to get this list via Bonjour/Rendezvous by executing this command:

mDNS -B _eppc._tcp local

... and then, from another terminal...

killall mDNS

(to stop the process).

All I really want is the information that comes up in the "Instance Name" column. Is there any way to do this using grep or something like it? Or even directly through AppleScript Studio? (Note you need Remote Apple Events enabled on at least one of the computers on your network to test this).

Any suggestions?

-Matt

[guardian34]

Would you post an example of mDNS' output? (I don't have a second Mac anymore.)

[MattPat]

Output of: mDNS -B _eppc._tcp local
(enclosed in code block to preserve whitespace)

Browsing for _eppc._tcplocal
Talking to DNS SD Daemon at Mach port 3843
Timestamp     A/R Flags Domain                   Service Type             Instance Name
15:44:18.030  Add     1 local.                   _eppc._tcp.              MATTMAC
15:44:18.033  Add     0 local.                   _eppc._tcp.              MACLAP

I somehow want to be able to get simply the list:
MATTMAC
MACLAP

-Matt

[guardian34]

I would try something like this:

do shell script "mDNS -B _eppc._tcplocal | colrm 1 74"
set hostList to paragraphs 4 through -1 of result

[MattPat]

This almost works perfectly.

The only problem: I have to manually kill off mDNS to get it to complete (it doesn't exit after printing output, it stays open and listens for more connections). I tried putting a "delay 1" followed by "killall mDNS" in the script, but AppleScript won't work like that... it wants to wait for the first script to complete before moving on.

Any suggestions?

-Matt

[hayne]

I have no experience with this, but I've seen that there is a "with timeout" clause available in AppleScript - maybe that would help.

[MattPat]

Tried it... with timeout only applies when you're referencing an application. It has no effect on other AppleScript commands

-Matt

[hayne]

One thing you could do is run the 'mDNS' in the background (outputting to a file) - that way your "do shell script" would return immediately and you could just do a 'delay 20' (or whatever) in your AppleScript and then do the 'killall'.

You start commands in the background in a shell script by appending a '&' at the end of the command.
You redirect the text that usually goes to the terminal into a file by using '>' followed by the name of the file you want to write to.

mDNS -B _eppc._tcplocal | colrm 1 74 > /tmp/myDnsOutput.txt &

[Raven]

I've posted a similar question in another thread not knowing there was one here... However I'm joining this one since its gone much further up to now. My only "question" even tough its nor realy one is: Since I need to have some output back from the command, but I do need to have it stop as it is the case for MattPat... So if I were to use the last command line Hayne suggested, the I could have a "proper" output to text file... Then would make more sense to get the info back form the text file in the script so its getting the info from a static file and not an interactive one like mDNS itself ?

[MattPat]

Well, that solution didn't quite work for me, but I was able to get it working: I wrote a shell script which I put in my application bundle that returns the same output as the above command, but terminates itself after 1 second.

#!/bin/bash

mDNS -B _eppc._tcp local | colrm 1 74 &
sleep 1
killall mDNS

It works perfectly for me Thanks for all your help, everyone!

-Matt

[MattPat]

Even better than my previously-posted example: you can put that shell script right into your AppleScript:

on getmDNS()
   set theScript to "mDNS -B _eppc._tcp local | colrm 1 74 &
sleep 1
killall mDNS"

   set hostList to paragraphs 4 thru -1 of (do shell script theScript)
   return hostList
end getmDNS

Now, call "getmDNS()" from anywhere in your AppleScript to get a list of all the hosts with this service.

set theHosts to getmDNS()

I did this because my program was failing if run from within its disk image because it couldn't properly get the bundle's Resources path. This way, there is no need to deal with extra files

-Matt

[bramley]

The man file for mDNS says this:

Quote: Originally Posted by man mDNS If you wish to perform DNS Service Discovery operations from a scripting language, then the best way to do this is not to execute the mDNS command and then attempt to decipher the textual output, but instead to directly call the DNS-SD APIs using a binding for your chosen language. For example, if you are programming in Ruby, then you can directly call DNS-SD APIs using the dnssd package documented at <http://rubyforge.org/projects/dnssd/>. Similar bindings for other languages are also in development.

I can't see any new packages in other languages, but assuming better Ruby skills than mine, it ought to be possible to call Ruby from Applescript.

[MattPat]

Well, it's true that this isn't the best way to do it... but it works, and there isn't an AppleScript binding that I (or anyone, apparently) am aware of. If I find anything new, I'll post it here, but for now this seems to accomplish the job.

-Matt