Ruby pipes: How do I tie the output of two subprocesses together?
Is there an automated way to do shell piping in Ruby? I'm trying to convert the following shell code to Ruby:
a | b | c... > ...
but the only solution I have found so far is to do the buffer management myself (simplified, untested, hope it gets my meaning across):
a = IO.popen('a')
b = IO.popen('b', 'w+')
Thread.new(a, b) { |in, out|
out.write(in.readpartial(4096)) until in.eof?
out.close_write
}
# deal with b.read...
I guess what I'm looking for is a way to tell popen to use an existing stream, instead of creating a new one? Or alternatively, an IO#merge method to connect a's output to b's input? My current approach becomes rather unwieldly when the number of filters grows.
I know about Kernel#system('a | b') obviously, but I need to mix Ruby filters with external program filters in a generic way.
Answer
Old question, but since its one of the first result on Google, here is the answer : http://devver.wordpress.com/2009/10/12/ruby-subprocesses-part_3/ (method 8)
In short :
sh = Shell.new
sh.system("a") | sh.system("b") | sh.system("c")
And you can do more complicated things like
sh.echo(my_string) | sh.system("wc") > "file_path"
xml = (sh.echo(html) | sh.system("tidy", "-q")).to_s