erlang日志功能。

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用cowboy这个库，没有日志功能，所以研究了otp提供的日志功能。

1.启动SASL的方式


erl –boot start_sasl 默认配置文件下启动SASL， {env, [{sasl_error_logger, tty},{errlog_type, all}]},，见源码 sasl.app文件。

erl -boot start_sasl -config xxxx.config  启动指定配置文件例如 elog1.config ，elog2.config 。。。配置文件默认目录是ebin，可自己指定目录。

还可以用 application:start(sasl). 在代码里启动应用。默认会读取代码ebin下的sasl.app，可去源码复制一份sasl.app然后修改 env参数。

sasl是通过application:get_env(sasl,xxx) 获得配置信息 。

2、sasl配置文件：

{env, [{sasl_error_logger, {file,"../../logs/error_logs/THELOG"}},%将sasl信息输出到文件中（不记录error_logger发送的信息）。另外，tty ：输出sasl信息到shell中（默认配置），false：不输出sasl信息。
     {errlog_type, all}, %过滤sasl_error_logger中的输出信息（error,progress）
     {error_logger_mf_dir,"../../logs/error_logs"}, %循环日志路径（记录sasl信息以及error_logger发送的信息）。
     {error_logger_mf_maxbytes,10485760},  %限定单个日志大小。
     {error_logger_mf_maxfiles,10}  %限定日志个数。
 ]}

3、error_logger：

参考官方文档

设置日志error_logger输出日志到文件：error_logger:logfile({open,Filename}).

注: 每次执行error_logger:logfile({open,Filename}).都会删掉之前Filename文件。

4、自定义日志功能：

由于业务需要，我想按照日期切分日志，该日志主要是为了记录业务操作。

思路:每次写日志到日志文件，先判断日志文件的最新修改日期是否跟当前日期一致，不一致就对该日志文件重命名（后缀添加日期)，并重新创建日志文件。

daylog_app.erl：

-module(daylog_app).
-behaviour(application).
-export([init/1]).
-export([start/0,start/2,stop/1]).
-define(SERVER,?MODULE).
-define(LOGFILE,"info.log").

start() ->
 application:start(daylog).

start(_StartType,_StartArgs) ->
 LogFile = get_app_env(log_file,?LOGFILE),
 supervisor:start_link({local,?SERVER},?MODULE,[daylog,LogFile]).

stop(_State) ->
 ok.


init([Module,LogFile]) ->
 Element = {Module,{Module,start_link,[LogFile]},
 temporary,2000,worker,[Module]}, %%如何启动和管理子进程
 Children = [Element] ,
 RestartStrategy = {one_for_one,0,1}, %%重启策略 
 {ok,{RestartStrategy,Children}}. %%监督规范

%%----------------------------------------------------------------------
%% Internal functions
%%----------------------------------------------------------------------
get_app_env(Opt, Default) ->
 case application:get_env(daylog, Opt) of
 {ok, Val} -> Val;
 _ ->
 case init:get_argument(Opt) of
 [[Val | _]] -> Val;
 error -> Default
 end 
 end.

daylog.erl

%%%-------------------------------------------------------------------
%%% Author : kingson <kingsoncai2013@gmail.com>
%%% Description : Cutting logs every day.
%%%
%%% Created : 4 Mar 2015 by kingson <kingsoncai2013@gmail.com>
%%%-------------------------------------------------------------------
-module(daylog).

-behaviour(gen_server).

%% API
-export([start_link/1]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
 terminate/2, code_change/3]).

-export([add_logfiles/1,info_log/1,info_log/2,logger/2,logger/3]).

-define(SERVER,?MODULE).
-record(state, {filename,other_files}).

add_logfiles(Files) ->
 gen_server:cast(?SERVER,{add_logfile,Files}).

info_log(Msg) -> %通知类型日志(默认)
 info_log(Msg,[]).
info_log(Format,Data) ->
 gen_server:cast(?SERVER,{accept,Format,Data}).

logger(FileName,Msg) ->
 logger(FileName,Msg,[]).
logger(FileName,Format,Data) ->
 gen_server:cast(?SERVER,{accept,FileName,Format,Data}).


%%====================================================================
%% API
%%====================================================================
%%--------------------------------------------------------------------
%% Function: start_link() -> {ok,Pid} | ignore | {error,Error}
%% Description: Starts the server
%%--------------------------------------------------------------------
start_link(LogFile) when is_list(LogFile) ->
 gen_server:start_link({local, ?SERVER}, ?MODULE, [LogFile], []).

%%====================================================================
%% gen_server callbacks
%%====================================================================

%%--------------------------------------------------------------------
%% Function: init(Args) -> {ok, State} |
%% {ok, State, Timeout} |
%% ignore |
%% {stop, Reason}
%% Description: Initiates the server
%%--------------------------------------------------------------------
init([LogFile]) ->
 process_flag(trap_exit, true),
 {ok,F} = file:open(LogFile,[append]),
 put(LogFile,F),
 {ok, #state{filename=LogFile},0}.

%%--------------------------------------------------------------------
%% Function: %% handle_call(Request, From, State) -> {reply, Reply, State} |
%% {reply, Reply, State, Timeout} |
%% {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, Reply, State} |
%% {stop, Reason, State}
%% Description: Handling call messages
%%--------------------------------------------------------------------
handle_call(_Request, _From, State) ->
 Reply = ok,
 {reply, Reply, State}.

%%--------------------------------------------------------------------
%% Function: handle_cast(Msg, State) -> {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State}
%% Description: Handling cast messages
%%--------------------------------------------------------------------
handle_cast({accept,Format,Data}, #state{filename=FileName}=State) ->
 write(Format,Data,FileName),
 {noreply, State};

handle_cast({accept,FileName,Format,Data},State) ->
 write(Format,Data,FileName),
 {noreply,State};

handle_cast({add_logfile,LogFiles},State) ->
 open_files(LogFiles),
 State2 = State#state{other_files=LogFiles},
 {noreply,State2};
 

handle_cast(_Msg, State) ->
 {noreply, State}.

%%--------------------------------------------------------------------
%% Function: handle_info(Info, State) -> {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State}
%% Description: Handling all non call/cast messages
%%--------------------------------------------------------------------
handle_info(timeout, State) ->
 gen_server:cast(?SERVER,{accept,"Has started daylog application~n",[]}),
 {noreply, State};

handle_info(_Info, State) ->
 {noreply, State}.

%%--------------------------------------------------------------------
%% Function: terminate(Reason, State) -> void()
%% Description: This function is called by a gen_server when it is about to
%% terminate. It should be the opposite of Module:init/1 and do any necessary
%% cleaning up. When it returns, the gen_server terminates with Reason.
%% The return value is ignored.
%%--------------------------------------------------------------------
terminate(_Reason, State) ->
 #state{filename=FileName,other_files=OtherFiles} = State,
 close_files(OtherFiles),
 F = get(FileName),
 io:format("Has stoped daylog application~n"),
 io:format(F,"Has stoped daylog application~n",[]),
 file:close(F),
 ok.

%%--------------------------------------------------------------------
%% Func: code_change(OldVsn, State, Extra) -> {ok, NewState}
%% Description: Convert process state when code is changed
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
 {ok, State}.

%%--------------------------------------------------------------------
%%% Internal functions
%%--------------------------------------------------------------------

write(Format,Data,Filename) ->
 LocalTime = calendar:local_time(),
 case filelib:last_modified(Filename) of
 {Last_Modified_Date,_} -> 
 {Today,_} = LocalTime,
 {Date_diff,_} = calendar:time_difference({Last_Modified_Date,{0,0,0}},{Today,{0,0,0}}),
 if Date_diff /= 0 -> %not the same date
 {Y,M,D} = Last_Modified_Date,
 Newname = Filename ++ "." ++ integer_to_list(Y) ++ "-" ++ integer_to_list(M) ++ "-" ++ integer_to_list(D), 
 file:close(get(Filename)),
 file:rename(Filename,Newname), 
 {ok,F} = file:open(Filename,[append]),
 put(Filename,F);
 true -> false
 end;
 0 -> false % the file does not exist.
 end,
 FileHandle = get(Filename),
 {{Year,Month,Day},{Hour,Minute,Second}} = LocalTime,
 do_write(FileHandle,"[~p-~p-~p T ~p:~p:~p] ", [Year,Month,Day,Hour,Minute,Second]), 
 Format2 = Format ++ "~n",
 do_write(FileHandle,Format2,Data).

do_write(FileHandle,Format,Data) ->
 io:format(Format, Data),
 io:format(FileHandle,Format,Data).
 

open_files([]) ->
 ok;
open_files([File|Others]) ->
 {ok,FileHandle} = file:open(File,[append]),
 put(File,FileHandle),
 open_files(Others).

close_files([]) ->
 ok;
close_files([File|Others]) ->
 FileHandle = get(File),
 file:close(FileHandle),
 close_files(Others).

daylog.app

{application,daylog, %%应用名
[ {description,""}, 
 {vsn,"0.1.0"},
 {modules,[]}, %%应用中的模块,可留空。 
 {registered,[]}, %%进程注册名，没进行实际注册操作,用于告知otp系统哪个进程注册了哪个名字,可留空
 {applications,[kernel,stdlib]}, %%先行启动的所有应用,不能留空
 {mod,{daylog_app,[]}}, %%指定应用启动模块,不能留空
 {env,[{log_file,"../../logs/info.log"}]}
]}.

compile.sh

for f in *.erl;do erlc +debug_info -o ../ebin $f;done

reference.txt

API Reference:
Module:daylog

add_logfiles(Files):
 Types:
 Files : a list for filenames 

info_log(Msg):
 Types:
 Msg: string
 descript:output log to default file which is descripted in ebin/daylog.app.
 
info_log(Format,Datas)
 Types:
 Format: string
 Datas: list for data

logger(FileName,Msg) ->
 Types:
 FileName: string
 Msg: String

logger(FileName,Format,Datas) ->
 Types:
 FileName: string
 Format: string
 Datas: list for data

erlang日志功能。

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原文地址：http://www.cnblogs.com/kingson-blog/p/4835044.html