[erlang-questions] Passing arguments to erlang from the command line

[Andy Khan]

Hi,

I'm playing with the pingpong example in the tutorial, and I'm trying to
launch the ping process directly from the command line.  When I run the
program as follows:

>erl -sname ping -run pingpong start_ping pong@bmt71

I get the following output:

=ERROR REPORT==== 17-Nov-2006::16:55:37 ===
Error in process <0.34.0> on node 'ping@bmt71' with exit value:
{badarg,[{pingpong,ping,2}]}

However, if I first start the erlang shell and then invoke the start_ping
method, everying works fine:

>erl -sname ping
Eshell V5.5.2  (abort with ^G)
(ping@bmt71)1> pingpong:start_ping(pong@bmt71).

I must be missing something about passing arguments from the command line
(I've shown my hacked about version of the ping code below).  Can anybody
help?

Regards
Andy

ping(N, Pong_Node) ->
    {pong, Pong_Node} ! {ping, self()},
    io:format("ping waiting for input~n", []),
    receive
        pong ->
            io:format("Ping received pong~n", [])
    end,
    ping(N - 1, Pong_Node).

start_ping(Pong_Node) ->
    spawn(pingpong, ping, [3, Pong_Node]).
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[Jani Hakala]

Andy Khan <[hidden email]> writes:

> Hi,
>
> I'm playing with the pingpong example in the tutorial, and I'm trying to
> launch the ping process directly from the command line.  When I run the
> program as follows:
>
>>erl -sname ping -run pingpong start_ping pong@bmt71
>
>From the erl man page:
 -run Mod [Func [Arg1, Arg2, ...]] (init flag):
      Makes init call the specified function. 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. See init(3).

So pong@bmt71 ends up being a string.

How about using -eval "pingpong:start_ping(pong@bmt71)"

Jani Hakala
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[Logan, Martin]

I wrote a small script to show you why this does not work



-module(test).

-export([test/1]).

test(Arg) ->
    io:format("arg = ~p~n", [Arg]).


I will first invoke the script from the erl shell and then from the
command line with the run option as you do.

---------- from the command shell  ------------

1> test:test(martin@logan).
arg = martin@logan
ok
2>


---------- from the command line  ------------

martinjlogan@core:~$ erl -run test test martin@logan
Erlang (BEAM) emulator version 5.4.12 [source] [hipe]

arg = ["martin@logan"]
Eshell V5.4.12  (abort with ^G)


See the problem? :)


Cheers,
Martin



-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Andy Khan
Sent: Friday, November 17, 2006 5:01 PM
To: [hidden email]
Subject: [erlang-questions] Passing arguments to erlang from the command
line

Hi,

I'm playing with the pingpong example in the tutorial, and I'm trying to

launch the ping process directly from the command line.  When I run the
program as follows:

>erl -sname ping -run pingpong start_ping pong@bmt71

I get the following output:

=ERROR REPORT==== 17-Nov-2006::16:55:37 ===
Error in process <0.34.0> on node 'ping@bmt71' with exit value:
{badarg,[{pingpong,ping,2}]}

However, if I first start the erlang shell and then invoke the
start_ping
method, everying works fine:

>erl -sname ping
Eshell V5.5.2  (abort with ^G)
(ping@bmt71)1> pingpong:start_ping(pong@bmt71).

I must be missing something about passing arguments from the command
line
(I've shown my hacked about version of the ping code below).  Can
anybody
help?

Regards
Andy

ping(N, Pong_Node) ->
    {pong, Pong_Node} ! {ping, self()},
    io:format("ping waiting for input~n", []),
    receive
        pong ->
            io:format("Ping received pong~n", [])
    end,
    ping(N - 1, Pong_Node).

start_ping(Pong_Node) ->
    spawn(pingpong, ping, [3, Pong_Node]).
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