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Hi all,

Is there a simple way to spawn an external program, feed its stdin, and
get its stdout?

The problem with popen is, if I want to feed a few MB's of input to it,
then it hangs (I suspect that its stdout IO buffer is full) before I
could read out its stdout on the next line. So, the following do not
work:

io=IO.popen("externalfilter")
io.write(verybigstring)
result=io.read

Thanks,
Ferenc

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On Sunday 18 January 2004 5:39 am, Ferenc Engard wrote:
> Hi all,
>
> Is there a simple way to spawn an external program, feed its stdin,
> and get its stdout?
>
> The problem with popen is, if I want to feed a few MB's of input to
> it, then it hangs (I suspect that its stdout IO buffer is full)
> before I could read out its stdout on the next line. So, the
> following do not work:
>
> io=3DIO.popen("externalfilter")
> io.write(verybigstring)
> result=3Dio.read

require 'open3'
Open3.popen3("externalfilter") { |sin,sout,serr|
sin.write(verybigstring)
result =3D sout.read
}

=2D-=20
Wesley J. Landaker -
OpenPGP FP: 4135 2A3B 4726 ACC5 9094 0097 F0A9 8A4C 4CD6 E3D2


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On Sun, 18 Jan 2004, Ferenc Engard wrote:

> Date: Sun, 18 Jan 2004 21:39:41 +0900
> From: Ferenc Engard <>
> Newsgroups: comp.lang.ruby
> Subject: running external process?
>
> Hi all,
>
> Is there a simple way to spawn an external program, feed its stdin, and
> get its stdout?
>
> The problem with popen is, if I want to feed a few MB's of input to it,
> then it hangs (I suspect that its stdout IO buffer is full) before I
> could read out its stdout on the next line. So, the following do not
> work:
>
> io=IO.popen("externalfilter")
> io.write(verybigstring)
io.close # the program is still reading it's stding here
> result=io.read
>
> Thanks,
> Ferenc

-a
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On Sunday 18 January 2004 8:26 am, Wesley J Landaker wrote:
> On Sunday 18 January 2004 5:39 am, Ferenc Engard wrote:
> > Hi all,
> >
> > Is there a simple way to spawn an external program, feed its stdin,
> > and get its stdout?
> >
> > The problem with popen is, if I want to feed a few MB's of input to
> > it, then it hangs (I suspect that its stdout IO buffer is full)
> > before I could read out its stdout on the next line. So, the
> > following do not work:
> >
> > io=3DIO.popen("externalfilter")
> > io.write(verybigstring)
> > result=3Dio.read
>
> require 'open3'
> Open3.popen3("externalfilter") { |sin,sout,serr|
> sin.write(verybigstring)
> result =3D sout.read
> }

Or (should have mentioned this in my first e-mail) if that still hangs,=20
you might try using Threads:

require 'open3'
Open3.popen3("externalfilter") { |sin,sout,serr|
threads =3D []
threads << Thread.new {
sin.write(verybigstring)
}
threads << Thread.new {
result =3D sout.read
}
threads.each {|t| t.join }
}

=2D-=20
Wesley J. Landaker -
OpenPGP FP: 4135 2A3B 4726 ACC5 9094 0097 F0A9 8A4C 4CD6 E3D2


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"Ferenc Engard" <> schrieb im Newsbeitrag
news:...
> Hi all,
>
> Is there a simple way to spawn an external program, feed its stdin, and
> get its stdout?
>
> The problem with popen is, if I want to feed a few MB's of input to it,
> then it hangs (I suspect that its stdout IO buffer is full) before I
> could read out its stdout on the next line. So, the following do not
> work:
>
> io=IO.popen("externalfilter")
> io.write(verybigstring)
> result=io.read

You need at least two threads or non blocking IO. How about:

IO.popen( "cat", "w+" ) do |io|
r = Thread.new(io) do |reader|
while ( line = reader.gets )
line.chomp!
$stdout.puts line
end
end

(1..100000).each {|i| io.puts i}
r.join
end

Regards

robert

> > The problem with popen is, if I want to feed a few MB's of input to it,
> > then it hangs (I suspect that its stdout IO buffer is full) before I
> > could read out its stdout on the next line. So, the following do not
> > work:
> >
> > io=IO.popen("externalfilter")
> > io.write(verybigstring)
> > result=io.read
>
> You need at least two threads or non blocking IO. How about:
>
> IO.popen( "cat", "w+" ) do |io|
> r = Thread.new(io) do |reader|
> while ( line = reader.gets )
> line.chomp!
> $stdout.puts line
> end
> end
>
> (1..100000).each {|i| io.puts i}
> r.join
> end

Thank you, this is what I need. Since I program in ruby, a 8-9 rows of
code seems too difficult to write by myself. :-/

Ferenc