How to pipe from one child process to another? about childprocess HOT 6 CLOSED

This is the best I could come up with so far. It hangs waiting for listing.

require 'childprocess'

keywords = %w(redis memcached)

r, w = IO.pipe

# Building "ps aux | grep 'redis|memcached'"
listing = ChildProcess.build("ps", "aux")
listing.io._stdin = File.open('/dev/null')
listing.io.stdout = w
listing.start

search = ChildProcess.build("grep", '-E', keywords.join('|'))
search.io._stdin = r
search.io.stdout = STDOUT
search.start

w.close
r.close
listing.wait
search.wait

puts 'DONE'

from childprocess.

The trick here is .duplex = true, which makes sure stdin is set in #start. Then you just need to get the order right.

This should work on at least Unix + JRuby (I don't have access to a Windows machine to test on at the moment):

require 'childprocess'

search = ChildProcess.build("grep", '-E', %w(redis memcached).join('|'))
search.duplex = true
search.io.stdout = STDOUT
search.start

listing = ChildProcess.build("ps", "aux")
listing.io.stdout = search.io.stdin
listing.start
listing.wait

search.io.stdin.close
search.wait

puts 'DONE'

Does that work for you?

PS. ❤️ your work!

from childprocess.

Thanks, that did the trick. Btw I'm really impressed with the code, but the documentation is weak. The readme needs more content to cover these various features. I'm going to cover childprocess in an upcoming blog post and that's my conclusion.

On 23 Nov 2012, at 17:53, Jari Bakken [email protected] wrote:

The trick here is .duplex = true, which makes sure stdin is set in #start. Then you just need to get the order right.

This should work on at least Unix + JRuby (I don't have access to a Windows machine to test on at the moment):

require 'childprocess'

listing = ChildProcess.build("ps", "aux")

search = ChildProcess.build("grep", '-E', %w(redis memcached).join('|'))
search.duplex = true
search.io.stdout = STDOUT
search.start

listing.io.stdout = search.io.stdin
listing.start
listing.wait

search.io.stdin.close
search.wait

puts 'DONE'
Does that work for you?

PS. your work!

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from childprocess.

Yeah, the README definitely needs improvement.

from childprocess.

I added some more examples to the README. Let me know if there's anything specific you'd like to see there.

from childprocess.

Fantastic, much better now. Thanks so much!

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