capturing standard out?

G

Giles Bowkett

Is there an easy way to capture standard out in Ruby, so that "puts"
throws its output into a buffer instead of just popping up on the
screen?
 
R

Robert Dober

Is there an easy way to capture standard out in Ruby, so that "puts"
throws its output into a buffer instead of just popping up on the
screen?

--
Giles Bowkett
http://www.gilesgoatboy.org
http://gilesbowkett.blogspot.com
http://giles.tumblr.com/

I have a scriopt producing output for bash, for running the test spec
I plugin output into an array, more or less like this:

class Output
@data =[]
class << self
attr_reader :data
end
end
if $TESTING then
def Kernl.puts *args, &blk
Output.data << args.join("")
Output.data << blk.call if blk
end
end

I have also Output.data.clear in #setup of the testsuite.

HTH
Robert
 
G

Gary Wright

Is there an easy way to capture standard out in Ruby, so that "puts"
throws its output into a buffer instead of just popping up on the
screen?

This is exactly the problem shell IO redirection was designed to solve.

$ ruby script.rb > output

What is the use case that prevents you from using shell redirection?



Gary Wright
 
D

Daniel Schierbeck

Is there an easy way to capture standard out in Ruby, so that "puts"
throws its output into a buffer instead of just popping up on the
screen?

You can set the $stdout global variable to point to whatever object you
like, as long as it adheres to a simple interface. Kernel#puts simply
redirects to $stdout.


Cheers,
Daniel
 
R

Robert Dober

You can set the $stdout global variable to point to whatever object you
like, as long as it adheres to a simple interface. Kernel#puts simply
redirects to $stdout.
That is a good idea too, especially with this idiom

def xxx(..., out = $stdout)

Robert
 
G

Giles Bowkett

You can set the $stdout global variable to point to whatever object you
like, as long as it adheres to a simple interface. Kernel#puts simply
redirects to $stdout.


Cheers,
Daniel

Hey Daniel, I found an example of the $stdout technique from Matz:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/15519

That's what I ended up using, although I used $stdout and instead of
$defout, and the documentation I found said assigning to $stdout is
deprecated in favor of $stdout.reopen, which I couldn't seem to get to
work for me.
 
G

Giles Bowkett

What is the use case that prevents you from using shell redirection?

I have no idea, I'm solving this for somebody I work with, but I'm
pretty confident they're familiar with shell redirection already.
Thanks tho.
 
E

Erik Veenstra

Here's a code snippet from my log library.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

----------------------------------------------------------------

["$stdout", "$stderr"].each do |std|
io = eval(std)
old_write = io.method:)write)

class << io
self
end.module_eval do
define_method:)write) do |text|
unless text =~ /^[\r\n]+$/ # Because puts calls twice.
File.open("logfile.log", "a") do |f|
f.puts [std[1..-1].upcase, caller[2], text].join(" ")
end
end

old_write.call(text)
end
end
end

$stdout.puts "text on stdout"
$stderr.puts "text on stderr"

----------------------------------------------------------------
 
J

James Edward Gray II

Is there an easy way to capture standard out in Ruby, so that "puts"
throws its output into a buffer instead of just popping up on the
screen?

I would do it like this:

#!/usr/bin/env ruby -w

require "stringio"

def capture_stdout(buffer = StringIO.new)
saved_stdout = $stdout
$stdout = buffer

yield

$stdout = saved_stdout

buffer.string rescue buffer
end

if __FILE__ == $PROGRAM_NAME
puts "This will be printed."
output = capture_stdout { puts "Meanwhile, this was captured." }
puts "This also will be printed."
p output
end

__END__

James Edward Gray II
 

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