| Author |
Message |
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| Sean.Hinde at one2one.co. |
 Posted: Wed Feb 23, 2000 4:17 pm |
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Guest
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Hi all,
I'm having a little difficulty with using a perl script as a port program:
#!/usr/local/bin/perl
while(1) {
$cmd = <STDIN>;
print STDERR "Received OK";
print "ok";
print STDERR "Sent";
}
My erlang port program:
Port = open_port({spawn, "perlscript"}, [stream]),
Port ! {self(), {command, "hello"}},
receive
Data ->
Data
after 10000
timedout
end
The result of this is that perl receives the hello message and prints
"Received OK" and "Sent" on stderr, but my erlang process never receives
"ok". Tracing confirms that the hello message is sent to the port but
nothing is received. Using an equivalent C program as the port program with
the same erlang code works fine.
Anyone any idea?
Sean
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| spearce at spearce.org |
| Posted: Wed Feb 23, 2000 4:33 pm |
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Guest
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Sean,
Perl output is typically line-buffered by default by Perl. This means
that the underlying OS will not receive any information to pass onto
another program (such as Erlang) unless a newline ("
") is printed in
Perl. Try doing the following before your while(1) loop starts:
select((select(STDOUT),$| = 1)[0]);
select((select(STDERR),$| = 1)[0]);
to unbuffer both the STDOUT and STDERR streams and see if that makes
a difference to your little program.
Sean Hinde <Sean.Hinde_at_one2one.co.uk> scrawled:
> Hi all,
>
> I'm having a little difficulty with using a perl script as a port program:
>
> #!/usr/local/bin/perl
> while(1) {
> $cmd = <STDIN>;
> print STDERR "Received OK";
> print "ok";
> print STDERR "Sent";
> }
>
> My erlang port program:
>
> Port = open_port({spawn, "perlscript"}, [stream]),
> Port ! {self(), {command, "hello"}},
> receive
> Data ->
> Data
> after 10000
> timedout
> end
>
> The result of this is that perl receives the hello message and prints
> "Received OK" and "Sent" on stderr, but my erlang process never receives
> "ok". Tracing confirms that the hello message is sent to the port but
> nothing is received. Using an equivalent C program as the port program with
> the same erlang code works fine.
--
Shawn.
``If this had been a real
life, you would have
received instructions
on where to go and what
to do.''
Post generated using Mail2Forum (http://m2f.sourceforge.net) |
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| bobsh at internetnw.net |
| Posted: Wed Feb 23, 2000 4:54 pm |
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Guest
|
The "ok" is probably stuck in a buffer, and you need to flush it. There's
at least one Perlism for that... I don't have a perl manual handy (and I
use Perl only rarely, so don't remember), but I do have some code that
needed to do that, and it uses "autoflush" and also "$|" might have
something to do with it.
On Wed, 23 Feb 2000, Sean Hinde wrote:
> Hi all,
>
> I'm having a little difficulty with using a perl script as a port program:
>
> #!/usr/local/bin/perl
> while(1) {
> $cmd = <STDIN>;
> print STDERR "Received OK";
> print "ok";
> print STDERR "Sent";
> }
>
> My erlang port program:
>
> Port = open_port({spawn, "perlscript"}, [stream]),
> Port ! {self(), {command, "hello"}},
> receive
> Data ->
> Data
> after 10000
> timedout
> end
>
> The result of this is that perl receives the hello message and prints
> "Received OK" and "Sent" on stderr, but my erlang process never receives
> "ok". Tracing confirms that the hello message is sent to the port but
> nothing is received. Using an equivalent C program as the port program with
> the same erlang code works fine.
>
> Anyone any idea?
>
> Sean
>
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| borys at bill3.ncats.net |
| Posted: Wed Feb 23, 2000 5:00 pm |
|
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Guest
|
> #!/usr/local/bin/perl
> while(1) {
> $cmd = <STDIN>;
> print STDERR "Received OK";
> print "ok";
> print STDERR "Sent";
> }
> The result of this is that perl receives the hello message and prints
> "Received OK" and "Sent" on stderr, but my erlang process never receives
> "ok". Tracing confirms that the hello message is sent to the port but
> nothing is received. Using an equivalent C program as the port program with
> the same erlang code works fine.
Try turning line buffering off by either setting $| to 1 or by
STDIN->autoflush(1). I imagine libc is waiting for a newline before it
*really* sends the data.
> Sean
Trannie
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| Sean.Hinde at one2one.co. |
| Posted: Wed Feb 23, 2000 5:28 pm |
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Guest
|
This one seems to work. Thanks for all your answers.
Sean
-----Original Message-----
From: Shawn Pearce [mailto:spearce_at_spearce.org]
Sent: 23 February 2000 16:34
To: erlang-questions_at_erlang.org
Subject: Re: Erlang ports and Perl
Sean,
Perl output is typically line-buffered by default by Perl. This means
that the underlying OS will not receive any information to pass onto
another program (such as Erlang) unless a newline ("
") is printed in
Perl. Try doing the following before your while(1) loop starts:
select((select(STDOUT),$| = 1)[0]);
select((select(STDERR),$| = 1)[0]);
to unbuffer both the STDOUT and STDERR streams and see if that makes
a difference to your little program.
Sean Hinde <Sean.Hinde_at_one2one.co.uk> scrawled:
> Hi all,
>
> I'm having a little difficulty with using a perl script as a port program:
>
> #!/usr/local/bin/perl
> while(1) {
> $cmd = <STDIN>;
> print STDERR "Received OK";
> print "ok";
> print STDERR "Sent";
> }
>
> My erlang port program:
>
> Port = open_port({spawn, "perlscript"}, [stream]),
> Port ! {self(), {command, "hello"}},
> receive
> Data ->
> Data
> after 10000
> timedout
> end
>
> The result of this is that perl receives the hello message and prints
> "Received OK" and "Sent" on stderr, but my erlang process never receives
> "ok". Tracing confirms that the hello message is sent to the port but
> nothing is received. Using an equivalent C program as the port program
with
> the same erlang code works fine.
--
Shawn.
``If this had been a real
life, you would have
received instructions
on where to go and what
to do.''
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| cheung |
| Posted: Tue Feb 21, 2012 3:30 am |
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Guest
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| wuji |
| Posted: Mon Sep 17, 2012 7:18 am |
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Joined: 10 Aug 2012
Posts: 654
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