Listening To Process Erlang

Question

I am trying to perform an action based on changes in the folder which are detected by synrc/fs library. I want to receive this notification every time the changes captured by fs & perform an action e.g. printing the changed filename.

I tried below code but executes only first time!

say_hello() ->
    fs:start_link(fs_watcher, "/Users/foldername"),
    fs:subscribe(fs_watcher),
    receive
        {Watcher_process, {Fs, File_event}, {ChangedFile, Type}} ->
            io:format("~p was ~p ~n",[ChangedFile,File_event])
    end.

Any useful help is appreciated along with link & description if possible! Thanks :)

@Dogbert you both gave me kinda similar answer!! appreciate a lot!! :) I have upvoted both of your answer!! but m confused whose answer to select (you both answer on exact time too) :| — nikdange_me, Mar 21 '17 at 15:03
@AsierAzkuenaga you both gave me kinda similar answer!! appreciate a lot!! :) I have upvoted both of your answer!! but m confused whose answer to select (you both answer on exact time too) :| — nikdange_me, Mar 21 '17 at 15:04

score 2 · Accepted Answer · answered Mar 21 '17 at 08:51

If you want the function to keep receiving the same kind of messages you could use recursion:

say_hello() ->
  fs:start_link(fs_watcher, "/Users/foldername"),
  fs:subscribe(fs_watcher),
  recur().

recur()->
  receive
     {Watcher_process, {Fs, File_event}, {ChangedFile, Type}} ->
         io:format("~p was ~p ~n",[ChangedFile,File_event]),
         recur()
  end.

You would have to then think about a way to finalise the function.

score 2 · Answer 2 · answered Mar 21 '17 at 08:52

2

You need to recursively call receive:

say_hello() ->
    fs:start_link(fs_watcher, "/Users/foldername"),
    fs:subscribe(fs_watcher),
    loop().

loop() ->
    receive
        {Watcher_process, {Fs, File_event}, {ChangedFile, Type}} ->
            io:format("~p was ~p ~n",[ChangedFile,File_event]),
            loop()
    end.

answered Mar 21 '17 at 08:52

Dogbert

212,659
41
396
397

Thanks, @Dogbert! :) – nikdange_me Mar 21 '17 at 14:59

Listening To Process Erlang

2 Answers2