Capturing standard out?


#1

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?


#2

On 3/19/07, Giles B. removed_email_address@domain.invalid wrote:

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


#3

On Mar 19, 2007, at 6:18 PM, Giles B. wrote:

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 W.


#4

On 3/19/07, Daniel S. removed_email_address@domain.invalid wrote:

On Tue, 2007-03-20 at 07:18 +0900, Giles B. wrote:

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.
That is a good idea too, especially with this idiom

def xxx(…, out = $stdout)

Robert


#5

On Tue, 2007-03-20 at 07:18 +0900, Giles B. wrote:

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


#6

On 3/19/07, Daniel S. removed_email_address@domain.invalid wrote:

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.


#7

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”


#8

On 3/19/07, Gary W. removed_email_address@domain.invalid wrote:

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.


#9

On Mar 19, 2007, at 5:18 PM, Giles B. wrote:

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 G. II