$$ terminal_logger1.erl
-module(terminal_logger1).
-behaviour(gen_event).
-export([init/1, handle_event/2, handle_call/2, handle_info/2, code_change/3, terminate/2]).
init(_Args) ->
{ok, []}.
handle_event(ErrorMsg, State) ->
io:format("*** Error1 *** ~p~n", [ErrorMsg]),
{ok, State}.
handle_call(_Request, _State) ->
{ok, [], []}.
handle_info(_Info, _State) ->
{ok, []}.
code_change(_OlvVsn, _State, _Extra) ->
ok.
terminate(_Args, _State) ->
ok.
$$ terminal_logger2.erl
-module(terminal_logger2).
-behaviour(gen_event).
-export([init/1, handle_event/2, handle_call/2, handle_info/2, code_change/3, terminate/2]).
init(_Args) ->
{ok, []}.
handle_event(ErrorMsg, State) ->
io:format("*** Error2 *** ~p~n", [ErrorMsg]),
{ok, State}.
handle_call(_Request, _State) ->
{ok, [], []}.
handle_info(_Info, _State) ->
{ok, []}.
code_change(_OlvVsn, _State, _Extra) ->
ok.
terminate(_Args, _State) ->
ok.
$$ terminal_logger3.erl
-module(terminal_logger3).
-behaviour(gen_event).
-export([init/1, handle_event/2, handle_call/2, handle_info/2, code_change/3, terminate/2]).
init(_Args) ->
{ok, []}.
handle_event(ErrorMsg, State) ->
io:format("*** Error3 *** ~p~n", [ErrorMsg]),
{ok, State}.
handle_call(_Request, _State) ->
{ok, [], []}.
handle_info(_Info, _State) ->
{ok, []}.
code_change(_OlvVsn, _State, _Extra) ->
ok.
terminate(_Args, _State) ->
ok.
编译：
Eshell> c(terminal_logger1). Eshell> c(terminal_logger2). Eshell> c(terminal_logger3).
运行：
D:\erl\code>erl
Eshell V5.6.3 (abort with ^G)
1> gen_event:start_link({local, error_man}).
{ok,<0.31.0>}
2> gen_event:add_handler(error_man, terminal_logger1, []).
ok
3> gen_event:add_handler(error_man, terminal_logger2, []).
ok
4> gen_event:add_handler(error_man, terminal_logger3, []).
ok
5> gen_event:which_handlers(error_man).
[terminal_logger3,terminal_logger2,terminal_logger1]
6> gen_event:notify(error_man, "Hideto").
*** Error3 *** "Hideto"
ok
*** Error2 *** "Hideto"
7> *** Error1 *** "Hideto"
7>