erlang代码片段

转载自http://blog.csdn.net/sw2wolf/article/details/6797708

.列表操作

lists:foreach(fun(X) -> io:format("E=~p~n",[X]) end, [1,2,3]).

lists:duplicate(10, 16#f).  % [15,15,15,15,15,15,15,15,15,15]

"abc-123" -> "abc"

no_vsn(Name) -> lists:takewhile(fun($-)->false;(_)-> true end,Name).

"abc-123" -> "123"

vsn(Name) ->

case lists:dropwhile(fun($-)->false;(_)->true end,Name) of

[_Sep|Vsn] -> Vsn;

_ -> "0"

end.

取偶数

EvenN = lists:filter(fun (N) -> N rem 2 == 0 end,lists:seq(1,100))

折叠

lists:foldl(fun(F, Last) -> F(Last) end, foo(), [fun whee/1, fun bar/1])

Fun = fun    (A = #auth{dir = [Dir]}, Acc) -> [{Dir, A}| Acc];    (A, Acc) -> [A| Acc]end,Authdirs = lists:foldr(Fun, [], SC#sconf.authdirs),

将URL中的空格换成+ UW = lists:map(fun($ )->$+;(C)->C end,Words)

判断是否为空格

is_nb_space(X) ->    lists:member(X, [$\s, $\t]).

>Data = [{"apple", "red"}, {"banana", "yellow"}, {"pear", "white"}].

>lists:keymember("pear",1,Data).

true

>lists:keydelete("banana",1,Data).  [{"apple","red"},{"pear","white"}]

>lists:keyreplace("apple",1,Data,{"tomato", "red"}).  [{"tomato","red"},{"banana","yellow"},{"pear","white"}]

> rd(user,{id,name}).   %% 用户记录

> lists:keysearch("wang", #user.name, [#user{id=1,name="li"}, #user{id=2,name="wang"}]).

> {value,#user{id = 2,name = "wang"}}

case lists:any(fun(Str) ->lists:prefix(Str, "redColor")end, ["apple","red"]) of   true -> {ok, Num, [H|T]};   false -> falseend

装载所有路径中的模块

[code:ensure_loaded(list_to_atom(filename:rootname(filename:basename(F)))) || P <-code:get_path(), F <-filelib:wildcard(P ++ "/*.beam")].

.二进制操作

-define(BYTE, 8/unsigned-big-integer).

<<C:2/unit:?BYTE>>  意思就是取两个单位，每单位8bits。

unit的默认值取决于type，如果type是integer或者float，则为1，binary为8。

<<C:4/binary, _/binary>>意思就是取4个单位，每单位8比特，总共4*8比特

1>A = <<1:32/little,1:8/little>>.   %低位在前<<1,0,0,0,1>>2> B = <<1:32/big,1:8/big>>.        %高位在前 <<0,0,0,1,1>>3> C = <<1:1,0:1>>.<<2:2>>

> B = <<3.2:32/big-float>>.> io:format("~w~n", [B]). > <<64,76,204,205>>> <<R:32/big-float>> = B. > R. > 3.200000047683716

<< PointID:32/unsigned-little-integer, Value:32/little-float>> = Bin.

bbsl(Bin,Shift) -> <<_:Shift,Rest/bits>> = Bin, <<Rest/bits,0:Shift>>.

>,,0,0,127,0>>>,,4,0,6,220,219,13>>>,,80>>131 is the version number, 97 is a small integer (8-bit), 98 is a big integer (32-bit), 110 (and 111) are for bignum integers. The rest is the data for the actual numbers.

对于utf相关类型，不能指定unit spec

utf8匹配1－4个bytes（参考RFC-2279） utf16匹配2 或 4 个bytes (参考 RFC-2781） utf32匹配4个 bytes

1> <<1024/utf8>>.<<208,128>> 2> <<1024/utf16>>.<<4,0>> 3> <<1024/utf32>>.<<0,0,4,0>>4> Bin = <<1024/utf8>>. <<208,128>> 5> <<U/utf8>> = Bin. <<208,128>> 6> U. 1024

.Binary Comprehensions

<< <<case X of $a -> $X; _ -> $Yend>> || <<X>><= <<"abcaa">> >>.

返回： <<"XYYXX">>

<< <<X>> || <<X:1>>  <= <<255, 3:2>> >>.

返回： <<1,1,1,1,1,1,1,1,1,1>>

1> B = erlang:md5("muzaaya").<<0,224,129,171,239,187,191,114,178,213,37,129,150,169,182,208>>2> lists:flatten([io_lib:format("~2.16.0b", [C]) || <<C>> <= B])."00e081abefbbbf72b2d5258196a9b6d0"

hexStr(B) 6#0F + 1, T))>> || <<X:8>> <= B >>.3> M:hexStr(erlang:md5("muzaaya")).<<"00E081ABEFBBBF72B2D5258196A9B6D0">>

.位操作

O2 = ((C1 band 16#03)bsl 4)bor (C2bsr 4).

. 文件操作

Destination = filename:join([code:root_dir(), "include", no_vsn( New_lib )]),

file:make_dir(Destination),

lists:foreach( fun(File) ->

FileName = lists:last(string:tokens(File,"/\\")),

file:copy(File, filename:join([Destination,FileName]))

end,

filelib:wildcard(filename:join([Source,"*"])) ).

w_ctl_file(Sid, Port, Key) ->case catch   begin     F = yaws:ctl_file(Sid),     error_logger:info_msg("Ctlfile : ~s~n", [F]),     file:write_file(F,io_lib:format("~w.", [{Port,Key}])),    {ok, FI} = file:read_file_info(F),    ok = file:write_file_info(F, FI#file_info{mode = 8#00600})   end of   {'EXIT', _} -> error;   _ -> okend.

remove(Path, File) ->    Desc = filename:join([Path,File]),    case filelib:is_dir(Desc) of    true ->        case file:list_dir(Desc) of        {ok,Sub} -> lists:foreach(fun(S) -> remove(Desc,S)end,Sub);        {error,Reason} -> io:format("error: ~p~n",[Reason])        end,        file:del_dir(Desc);    false ->        file:delete(Desc)    end.

file:write_file("test.txt", "12 13 14 15 16 17 18").

{ok, Bin} = file:read_file(File),

Rules = string:tokens(erlang:binary_to_list(Bin), "\n").

case file:open(File, [write]) of        {ok, FD} ->            %io:put_chars(FD, Text), <-- ERROR            ok = file:close(FD),

file:write_file(File,unicode:characters_to_binary(Text));   < -- HACK

{error, R} ->            R1 = file:format_error(R),            report("could not write file '~s': ~s.", [File, R1]),            exit(error)

end.

或

file:open(File, [write, {encoding, utf8}]).

{ok, Fd} = file:open("test_data.dat", [binary, write]),ok = file:write(Fd,lists:duplicate(100, "1")), ok = file:close(Fd).

.日期,时间操作

{{Y,M,D},{H,M,S}} = calendar:local_time().

calendar:datetime_to_gregorian_seconds(calendar:local_time()). calendar:day_of_the_week(2009,2,24).

next_day({Y, M, D}) ->    Day1 = calendar:date_to_gregorian_days(Y, M, D),    calendar:gregorian_days_to_date(Day1 + 1).

w3cdtf(GregSecs) ->

Date = calendar:gregorian_seconds_to_datetime(GregSecs),    {{Y, Mo, D},{H, Mi, S}} = Date,    [UDate|_] = calendar:local_time_to_universal_time_dst(Date),    {DiffD,{DiffH,DiffMi,_}}=calendar:time_difference(UDate,Date).

.字符串操作

count_chars(String, Char) ->    length([X || X <- String, X == Char]).

格式化字符串, 像C语言的sscanf()

Cmd = io_lib:format(\"cd ~s/include; rm ~s; ln -s ../lib/~s/include ~s\", [code:root_dir(), no_vsn( New_lib ), New_lib, no_vsn( New_lib )]),

os:cmd(Cmd);

PN = [erlang:list_to_integer(N) || N <-string:tokens( vsn( Package_that_might_be_newer ), "." )],

packages_from_html(Html,Packages) ->    case string:str(Html,"class=\"package\"") of    0 -> Packages;    Start ->         Sub = string:sub_string(Html,Start),        T1 = string:sub_string(Sub,string:chr(Sub,$>)+1),        PName = string:sub_string(T1,1,string:chr(T1,$<)-1),        T2 = string:sub_string(T1,string:str(T1,"<i>")+3),        Descr = string:sub_string(T2,1,string:str(T2,"</i>")-1),        packages_from_html(T2,[{PName,Descr}|Packages])    end.

当使用Erlang程序与其它语言程序通讯时，可能需要把一个字符串转换成为Erlang的Term，可以这样实现{ok, Tokens, _} = erl_scan:string(String),{ok, Term} = erl_parse:parse_term(Tokens).注意这里的String需要以句号结尾。例如在erlang shell下：> {ok, Tokens, _} = erl_scan:string("{1, {2}, [3]}.").> {ok, {X, Y, Z}} = erl_parse:parse_term(Tokens).

.正则表达式

>[NoRed,NoBlue] = re:split("1 2 3 - 5 6", "-", [{return,list}]).

["1 2 3 ","5 6"]

>{ok, P} =re:compile("\xE2\x80\x93").{ok,{re_pattern,0,0,  <<69,82,67,80,53,0,0,0,0,0,0,0,6,0,0,0,0,0,0,0,226,0,147,...>>}}> re:split([48,32,226,128,147,32,49],P, [{return, list}]).["0 "," 1"]

.端口操作1>Port = open_port({spawn, "cat"}, [stream]).#Port<0.522>2> port_command(Port, "Hello World\n").true3> flush().Shell got {#Port<0.522>,{data,{eol,"Hello World\n"}}}ok4> port_close(Port).true

 

spawn_link(fun() -> tbz2(YPid, Dir)end),

tbz2(YPid, Dir) ->   process_flag(trap_exit, true),     P = open_port({spawn, "tar cj ."},[{cd, Dir},use_stdio,binary,exit_status]),   stream_loop(YPid, P).stream_loop(YPid, P) ->receive   {P, {data, Data}} ->     yaws_api:stream_chunk_deliver_blocking(YPid, Data),     stream_loop(YPid, P);   {P, {exit_status, _}} ->     yaws_api:stream_chunk_end(YPid);   {'EXIT', YPid, Status} ->    exit(Status);   Else ->    error_logger:error_msg("Could not deliver zip file: ~p\n", [Else])end.

 

getuid() ->      case os:type() of          {win32, _} -> {ok, "0"};          _ ->              load_setuid_drv(),              P = open_port({spawn, "setuid_drv g"},[]),              receive                  {P, {data, "ok " ++ IntList}} ->  {ok, IntList}              end      end.load_setuid_drv() ->      Path = case yaws_generated:is_local_install() of          true -> filename:dirname(code:which(?MODULE)) ++ "/../priv/lib";          false ->              PrivDir = code:priv_dir(yaws),              filename:join(PrivDir,"lib")      end,      case erl_ddll:load_driver(Path, "setuid_drv") of          ok -> ok;         {error, Reason} ->              error_logger:format("Failed to load setuid_drv (from ~p) : ~p",[Path, erl_ddll:format_error(Reason)]),              exit(normal)     end.

例外处理

 

call(URL, Options, Payload) ->try   {ok, CallPayloadDeep} = encode_call_payload(Payload)，   CallPayload = lists:flatten(CallPayloadDeep)，   {ok, Response} = http:request(post, {URL,       [{"Content-length",length(CallPayload)}],       "application/x-www-form-urlencoded",CallPayload},Options, [])，   RespBody= if (size(Response) == 2)or (size(Response) == 3) ->                element(size(Response), Response)             end,   decode_call_payload(RespBody)catch error:Err ->error_logger:error_report([                         {'json_rpc:call', error},{error, Err},                         {stack, erlang:get_stacktrace()}]),                   {error,Err}

catch _:_ -> ignore

end.

validate(A, B) -> try    mnesia:transaction((fun my_funky_mnesia_test/2)(A,B)) catch    exit:{aborted, all_valid} -> ok;    exit:{aborted, Error} -> {error, Error} end. -spec my_funky_mnesia_test(some_t(), another_t()) ->no_return().my_funky_mnesia_test(A, B) ->    some_test_db_operations(A, B),    mnesia:abort(all_valid).

嵌套记录

-record(name, {first = "Robert", last = "Ericsson"}). -record(person, {name = #name{}, phone}). demo() ->     P = #person{name= #name{first="Robert",last="Virding"}, phone=123},

First = (P#person.name)#name.first.

动态运行代码1> FunStr = "fun (A) -> A+B end.". 2> {ok, Tokens, _} = erl_scan:string(FunStr).3> {ok, [Form]} = erl_parse:parse_exprs(Tokens).4> Bindings = erl_eval:add_binding('B', 2, erl_eval:new_bindings()).5> {value, Fun, _} =erl_eval:expr(Form, Bindings).6> Fun(1).

remote_load_code(Module, Node) ->     {_, Binary, Filename} = code:get_object_code(Module),     rpc:call(Node,code,load_binary, [Module, Filename, Binary])

进程关系

Start the supervisor: 1> {ok, Sup} = supervisor:start_link(ignore_sup, []). {ok,<0.43.0>} It has no children: 2> supervisor:which_children(Sup). [] Starting the child: 3> supervisor:start_child(Sup, []). =ERROR REPORT==== 13-Apr-2011::18:59:01 === Ignoring: <0.46.0> {ok,undefined} The child specification is installed: 4> supervisor:which_children(Sup). [{undefined,undefined,worker,[ignore_server]}]But the child process reported above is not alive:5> is_process_alive(list_to_pid("<0.46.0>")). false

info(PlayerId) ->    Pid = case global:whereis_name(util:getRegName({?MODULE, PlayerId})) of    P when is_pid(P) -> P;    _ ->        {ok, P} = player_sup:start_child(PlayerId),         P   end,   gen_server:call(Pid, info).

进制转换

integer_to_hex(I) ->      case ) of          {'EXIT', _} ->               old_integer_to_hex(I);          Int ->               Int      end.old_integer_to_hex(I) ).%% string_to_hexstring_to_hex(String) ->      HEXC = fun (D)when D > 9 -> $a + D - 10;                 (D) -> $0 + D             end,      lists:foldr(fun (E, Acc) ->              [HEXC(E div 16),HEXC(Erem 16)|Acc] end, [], String).%% hex_to_stringhex_to_string(Hex) ->      DEHEX = fun (H)when H >= $a -> H - $a + 10;                  (H) when H >= $A -> H - $A + 10;                  (H) -> H - $0              end,  {String, _} =lists:foldr(fun

(E, {Acc, nolow}) -> {Acc, DEHEX(E)};           (E, {Acc, LO}) -> {[DEHEX(E)*16+LO|Acc], nolow}      end, {[], nolow}, Hex),      String.数据结构stdlib中包含大量的数据结构如lists，array，dict，gb_sets，gb_trees，ets，dets等

.gb_trees1>X = gb_trees:from_orddict(orddict:from_list([{trace,false},{limit,-1},{timeout,-1}])). {3,{timeout,-1,{limit,-1,nil,nil},{trace,false,nil,nil}}}2>gb_trees:update(limit,true,X).{3,{timeout,-1,{limit,true,nil,nil},{trace,false,nil,nil}}}

.ets/dets

E = ets:new(my_code, [public,set]),ets:match_delete (E,'_'),

ets:insert(E, {num_files, 0}),ets:insert(E, {num_bytes, 0}).

%% T = ets:new(?MODULE, [{write_concurrency, true}]).

{ok,?MODULE}=dets:open_file(?MODULE,[{type,set},{file,"fcnum.dets"}]),dets:insert(?MODULE, {1, [1,2,3,4,5,6,7]}),

dets:insert(?MODULE, {1, [7,6,5,4,3,2,1]}),dets:close(?MODULE).

>Table = ets:new(foobar, [set,public]).>ets:tab2list(Table).[]> ets:insert(Table, {1}).true> ets:insert(Table, {2}).true> ets:tab2list(Table).[{1},{2}]

ets:new(test, [named_table, set, protected]),ets:insert(test, {a, 1, true, true}),ets:insert(test, {b, 2, true, true}),ets:insert(test, {c, 3, true, true}),ets:insert(test, {d, 2, true, true}),ets:insert(test, {e, 1, true, true}),  %ets:match_delete(test, [{['_', '$1', '_', '_'], [{'>', '$1', 2}], []}]),

N = ets:select_delete(test, [{{'$1', '$2', '$3', '$4'}, [{'>', '$2', 2}], [true]}]),

1> rd(data, {id, nick}).data2> rd(wrapper, {id, data}).wrapper3> L = [#wrapper{id=1,data=#data{id=1}},#wrapper{id=2,data=#data{id=2,nick=n}}].[#wrapper{id = 1,data = #data{id = 1,nick = undefined}},#wrapper{id = 2,data = #data{id = 2,nick = n}}]4> qlc:e(qlc:q([W ||#wrapper{data =#data{nick = N}} =W < - L, N =/=undefined])).[#wrapper{id = 2,data = #data{id = 2,nick = n}}]

.系统管理

%查看节点的内存消耗

> erlang:memory().

%查看进程占用内存 > spawn(fun() -> etop:start([{output, text}, {interval, 1}, {lines, 20}, {sort, memory}]) end).

%查看进程状态 > erlang:process_info(pid(X,Y,Z)).

%查看系统字长

>erlang:system_info(wordsize).

%手动gc回收 > erlang:garbage_collect(pid(X,Y,Z)).