如果你需要真正快速的IO，那么你必须做比平常更棘手一点。

  -module（g）。 
 -export（[s / 0]）。 
 s（） - > 
 P = open_port（{fd，0，1}，[in，binary，{line，256}]），
 r（P，0，0），
 halt（）。 
 r（P，C，L） - > 
接收
 {P，{data，{eol，< $>：8，_ / binary>>}}}  - > 
 r（P，C + 1，L）; 
 {P，{data，{eol，Line}}}  - > 
 r（P，C，L + size（Line））; 
 {'EXIT'，P，normal}  - > 
 io：format（〜p〜n，[L / C]）
 end。 
 

它是我知道的最快的IO，但注意 -noshell -noinput 。
编译就像 erlc + native +{hipe，[o3]}g.erl 但使用 -smp disable

  erl -smp disable -noinput -mode minimal -boot start_clean -s erl_compile compile_cmdline @cwd / home / hynek /下载@option native @option'{hipe，[o3]}'@files g.erl 
 

并运行：

  time erl -smp disable -noshell -mode minimal -boot start_clean -noinput -sgs< uniprot_sprot.fasta 
 352.6697028442464 

 real 0m3.241s 
用户0m3.060s 
 sys 0m0.124s 
 

使用 -smp启用但本机需要：

  $ erlc + native +{hipe，[o3]}g.erl 
 $ time erl -noshell -mode最小-boot start_clean -noinput -sg s< uniprot_sprot $。 $ p> 

字节代码，但带有 -smp disable （几乎与native一样，因为大部分工作都是在端口完成的） ：
  $ erlc g.erl 
 $ time erl -smp disable -noshell -mode最小-boot start_clean -noinput -sg s< uniprot_sprot.fasta 
 352.6697028442464 

 real 0m3.565s 
用户0m3.436s 
 sys 0m0.104s 
 
仅用于smp完整的字节码：
  $ time erl -noshell -mode minimal -boot start_clean -noinput -sg s< uniprot_sprot.fasta 
 352.6697028442464 

 real 0m5.433s 
用户0m5.236s 
 sys 0m0.128s 
 
比较 sarnold  版本给我错误的答案，并且需要更多的相同的HW：
  $ erl -smp disable -noinput -mode minimal -boot start_clean -s erl_compile compile_cmdline @cwd / home / hynek /下载@option native @option'{hipe，[o3]}'@files golf.erl 
 ./golf.erl:5：Warning：variable'休息'未使用
 $ time erl -smp disable -noshell -mode最小-s高尔夫测试
 359.04679841439776 

 real 0m17.569s 
用户0m16.749s 
 sys 0m0.664s 
 
 编辑：我已经看过 uniprot_sprot.f asta ，我有点惊讶。它是3824397行和232MB。这意味着 -smp禁用版本可以处理每秒118万个文本行（71MB / s的线性IO）。
 
I'm trying to get the mean length of fasta sequences using Erlang. A fasta file looks like this
>title1
ATGACTAGCTAGCAGCGATCGACCGTCGTACGC
ATCGATCGCATCGATGCTACGATCGATCATATA
ATGACTAGCTAGCAGCGATCGACCGTCGTACGC
ATCGATCGCATCGATGCTACGATCTCGTACGC
>title2
ATCGATCGCATCGATGCTACGATCTCGTACGC
ATGACTAGCTAGCAGCGATCGACCGTCGTACGC
ATCGATCGCATCGATGCTACGATCGATCATATA
ATGACTAGCTAGCAGCGATCGACCGTCGTACGC
>title3
ATCGATCGCATCGAT(...)

I tried to answser this question using the following Erlang code:
-module(golf).
-export([test/0]).

line([],{Sequences,Total}) ->  {Sequences,Total};
line(">" ++ Rest,{Sequences,Total}) -> {Sequences+1,Total};
line(L,{Sequences,Total}) -> {Sequences,Total+string:len(string:strip(L))}.

scanLines(S,Sequences,Total)->
        case io:get_line(S,'') of
            eof -> {Sequences,Total};
            {error,_} ->{Sequences,Total};
            Line -> {S2,T2}=line(Line,{Sequences,Total}), scanLines(S,S2,T2)
        end  .

test()->
    {Sequences,Total}=scanLines(standard_io,0,0),
    io:format("~p\n",[Total/(1.0*Sequences)]),
    halt().

Compilation/Execution:
erlc golf.erl
erl -noshell -s golf test < sequence.fasta
563.16

this code seems to work fine for a small fasta file but it takes hours to parse a larger one (>100Mo). Why ? I'm an Erlang newbie, can you please improve this code ?

If you need really fast IO then you have to do little bit more trickery than usual.
-module(g).
-export([s/0]).
s()->
  P = open_port({fd, 0, 1}, [in, binary, {line, 256}]),
  r(P, 0, 0),
  halt().
r(P, C, L) ->
  receive
    {P, {data, {eol, <<$>:8, _/binary>>}}} ->
      r(P, C+1, L);
    {P, {data, {eol, Line}}} ->
      r(P, C, L + size(Line));
    {'EXIT', P, normal} ->
      io:format("~p~n",[L/C])
  end.

It is fastest IO as I know but note -noshell -noinput.
Compile just like erlc +native +"{hipe, [o3]}" g.erl but with -smp disable
erl -smp disable -noinput -mode minimal -boot start_clean -s erl_compile compile_cmdline @cwd /home/hynek/Download @option native @option '{hipe, [o3]}' @files g.erl

and run:
time erl -smp disable -noshell -mode minimal -boot start_clean -noinput -s g s < uniprot_sprot.fasta
352.6697028442464

real    0m3.241s
user    0m3.060s
sys     0m0.124s

With -smp enable but native it takes:
$ erlc +native +"{hipe, [o3]}" g.erl
$ time erl -noshell -mode minimal -boot start_clean -noinput -s g s<uniprot_sprot.fasta
352.6697028442464

real    0m5.103s
user    0m4.944s
sys     0m0.112s

Byte code but with -smp disable (almost in par with native because most of work is done in port!):
$ erlc g.erl
$ time erl -smp disable -noshell -mode minimal -boot start_clean -noinput -s g s<uniprot_sprot.fasta
352.6697028442464

real    0m3.565s
user    0m3.436s
sys     0m0.104s

Just for completeness byte code with smp:
$ time erl -noshell -mode minimal -boot start_clean -noinput -s g s<uniprot_sprot.fasta 
352.6697028442464

real    0m5.433s
user    0m5.236s
sys     0m0.128s

For comparison sarnold version gives me wrong answer and takes more on same HW:
$ erl -smp disable -noinput -mode minimal -boot start_clean -s erl_compile compile_cmdline @cwd /home/hynek/Download @option native @option '{hipe, [o3]}' @files golf.erl
./golf.erl:5: Warning: variable 'Rest' is unused
$ time erl -smp disable -noshell -mode minimal -s golf test
359.04679841439776

real    0m17.569s
user    0m16.749s
sys     0m0.664s

EDIT: I have looked at characteristics of uniprot_sprot.fasta and I'm little bit surprised. It is 3824397 rows and 232MB. It means that -smp disabled version can handle 1.18 million text lines per second (71MB/s in line oriented IO).