转自： http://blogold.chinaunix.net/u3/104903/showart_2074188.html
.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 -> false
end
.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.
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; _ -> $Y end>> || <<X>> <= <<"abcaa">> >>.
返回： <<"XYYXX">>
<< <<X>> || <<X:1>> <= <<255, 3:2>> >>.
返回： <<1,1,1,1,1,1,1,1,1,1>>
.位操作
O2 = ((C1 band 16#03) bsl 4) bor (C2 bsr 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;
_ -> ok
end.
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: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).
.端口操作
1>Port = open_port({spawn, "cat"}, [stream]).
#Port<0.522>
2> port_command(Port, "Hello World\n").
true
3> flush().
Shell got {#Port<0.522>,{data,{eol,"Hello World\n"}}}
ok
4> 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
进制转换
integer_to_hex(I) ->
case catch erlang:integer_to_list(I, 16) of
{'EXIT', _} ->
old_integer_to_hex(I);
Int ->
Int
end.
old_integer_to_hex(I) when I<10 ->
integer_to_list(I);
old_integer_to_hex(I) when I<16 ->
[I-10+$A];
old_integer_to_hex(I) when I>=16 ->
N = trunc(I/16),
old_integer_to_hex(N) ++ old_integer_to_hex(I rem 16).
%% hex_to_integer
hex_to_integer(Hex) ->
erlang:list_to_integer(Hex, 16).
%% string_to_hex
string_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(E rem 16)|Acc] end, [], String).
%% hex_to_string
hex_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_trees
1>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}]
1> rd(data, {id, nick}).
data
2> rd(wrapper, {id, data}).
wrapper
3> 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}}]
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