how to capture io:format's output using ei?

Serge Aleynikov <>
Wed Oct 19 13:50:15 CEST 2005


Uffe,

Thank you for your comments.  Perhaps someone from the ei's OTP support 
team can shed some light on this issue.  The open question is:

As Uffe pointed out we can register a local process 'user' using ei's 
ei_publish() function (along with bind() and listen() on an open 
socket).  However, then it forces us to use io:format(user, Format, 
Args) function on the server node, and if I understand this correctly, 
the output of io:format/2 won't be sent to the remote C client caller.

Is there a "correct" (i.e. preferred) way of doing this in C, so that 
output of both io:format/[2,3] could be captured at the remote node 
invoking the ei_rpc(), and that io:format/[2,3] would understand tildes?

Thanks.

Serge


Ulf Wiger wrote:
> Den 2005-10-18 19:25:16 skrev Serge Aleynikov <>:
> 
>> Interesting...
>>
>> Though in my case even if I use "~n" then nothing gets returned.  If 
>> I  use "\n" then, 'ok' gets returned, however, a "Test string\n" gets  
>> printed in the shell window of the  node:
>>
>> devlinuxpro2> ./erl_call -sname  -a 'io format ["Test  
>> string~n"]'
>> devlinuxpro2>
>>
>> ()9>
>> ()9>
>>
>> devlinuxpro2> ./erl_call -sname  -a 'io format ["Test  
>> string\n"]'
>> ok          <-- the result of a call got printed
>> devlinuxpro2>
>>
>> ()9> Test string\n     <-- this is printed in the shell
>> ()9>
> 
> 
> Yes, this was exactly what I got too.
> Something in the chain chokes on the tilde. Remove it, and you
> can get a printout of sorts, but io:format/2 without tildes is
> a bit limited...
> 
> 
>> So, the original question still stands: could you tell how to 
>> redirect  the output when using the ei's rpc call?
> 
> 
> I have not looked into ei at all. The standard way to make sure that
> io gets executed on the remote node is to either set the group leader
> of the remote process to some standard group leader on the remote
> node (per default in an rpc:call(), the group leader is the calling
> process, which makes sense if the remote node e.g. doesn't have io
> capabilities).
> 
> If you specify the destination in the io:format/3 call:
> 
> io:format(user, "Hello~n", [])
> 
> then the locally registered process 'user' will be used to
> handle the output. Note that on a node started with -noshell,
> whereis(user) -> undefined. This means nothing will get
> printed ;-), but rpc:call(Remote, io, format, [user,"...",[]])
> will still return 'ok'.
> 
> Again, this is how it works with normal rpc. Don't know about ei.
> 
> /Uffe



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