how to call os:cmd("ls") from shell?（老掉牙问题）

之前erlang邮件列表的一个问题：

hi list,

I fellowed the otp document, but it failed.

# erl -s os cmd ls

Erlang (BEAM) emulator version 5.5.5 [source] [async-threads:0] [hipe]
[kernel-poll:false] [lock-checking]

{"init terminating in
do_boot",{function_clause,[{os,validate1,[[ls]]},{os,cmd,1},{init,start_it,1},{init,start_em,1}]}}

Crash dump was written to: erl_crash.dump


Thx,
Jeremy
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[email protected] to erlanging, erlang-questio.

show details 7/11/07



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echo 'os:cmd("ls").' | erl

cheers
Y.

----Message d'origine----
>Date: Wed, 11 Jul 2007 14:06:43 +0800
>De: "Jeremy Chow" <[email protected]>
>A: [email protected]
>Sujet: [erlang-questions] how to call os:cmd("ls") from shell?
- Show quoted text -
>
>hi list,
>
>I fellowed the otp document, but it failed.
>
># erl -s os cmd ls
>
>Erlang (BEAM) emulator version 5.5.5 [source] [async-threads:0] [hipe]
>[kernel-poll:false] [lock-checking]
>
>{"init terminating in
>do_boot",{function_clause,[{os,validate1,[[ls]]},{os,cmd,1},{init,start_it,1},{init,start_em,1}]}}
>
>Crash dump was written to: erl_crash.dump
>
>
>Thx,
>Jeremy
>_______________________________________________
>erlang-questions mailing list
>[email protected]
>http://www.erlang.org/mailman/listinfo/erlang-questions
>

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Bengt Kleberg to erlang-questio.

show details 7/11/07



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On 2007-07-11 08:06, Jeremy Chow wrote:
> hi list,
>
> I fellowed the otp document, but it failed.
>
> # erl -s os cmd ls

this will not work.
1 erl -s will bundle the arguments (ls) into a list as atoms.
       os:cmd( [ls] ).
2 os:cmd/1 wants a string. os:cmd("ls").


one might think that
erl -run os cmd ls
will work since -run keeps the arguments as strings, but -run also
bundles all arguments into a single string.

so you have to write an interface module that calls os:cmd/1 for you.


bengt
--
Those were the days...
   EPO guidelines 1978: "If the contribution to the known art resides
   solely in a computer program then the subject matter is not
   patentable in whatever manner it may be presented in the claims."
- Show quoted text -

参见init 文档：

-eval Expr
    Scans, parses and evaluates an arbitrary expression Expr during system initialization. If any of these steps fail (syntax error, parse error or exception during evaluation), Erlang stops with an error message. Here is an example that seeds the random number generator:

    % erl -eval '{X,Y,Z}' = now(), random:seed(X,Y,Z).'

    This example uses Erlang as a hexadecimal calculator:

    % erl -noshell -eval 'R = 16#1F+16#A0, io:format("~.16B~n", [R])' \
    -s erlang halt
    BF
           

    If multiple -eval expressions are specified, they are evaluated sequentially in the order specified. -eval expressions are evaluated sequentially with -s and -run function calls (this also in the order specified). As with -s and -run, an evaluation that does not terminate, blocks the system initialization process.
-extra
    Everything following -extra is considered plain arguments and can be retrieved using get_plain_arguments/0.
-run Mod [Func [Arg1, Arg2, ...]]
    Evaluates the specified function call during system initialization. Func defaults to start. If no arguments are provided, the function is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, taking the list [Arg1,Arg2,...] as argument. All arguments are passed as strings. If an exception is raised, Erlang stops with an error message.
    Example:

    % erl -run foo -run foo bar -run foo bar baz 1 2

    This starts the Erlang runtime system and evaluates the following functions:

    foo:start()
    foo:bar()
    foo:bar(["baz", "1", "2"]).
           

    The functions are executed sequentially in an initialization process, which then terminates normally and passes control to the user. This means that a -run call which does not return will block further processing; to avoid this, use some variant of spawn in such cases.
-s Mod [Func [Arg1, Arg2, ...]]
    Evaluates the specified function call during system initialization. Func defaults to start. If no arguments are provided, the function is assumed to be of arity 0. Otherwise it is assumed to be of arity 1, t aking the list [Arg1,Arg2,...] as argument. All arguments are passed as atoms. If an exception is raised, Erlang stops with an error message.
    Example:

    % erl -s foo -s foo bar -s foo bar baz 1 2

    This starts the Erlang runtime system and evaluates the following functions:

    foo:start()
    foo:bar()
    foo:bar([baz, '1', '2']).
           

    The functions are executed sequentially in an initialization process, which then terminates normally and passes control to the user. This means that a -s call which does not return will block further processing; to avoid this, use some variant of spawn in such cases.
    Due to the limited length of atoms, it is recommended that -run be used instead.

还可以这样:
erl -noshell -eval 'os:cmd("ls").' -s init stop


但是因为没有shell所以目录的内容没有被列出来。

貌似没有最好的方案!!!