Ruby method with block variable scope?

Question

I was curious if it was even possible to pass in a block into a method(s) that could manipulate that method's local variables. I have a net/ssh helper method that I would like to have an optional expect-like block:

def ssh_exec!(session,cmd,override=false, &block)
  stdout_data = ""
  stderr_data = ""
  exit_code = ""
  exit_signal = ""
  session.open_channel do |channel|
    channel.request_pty do |c, success|
      if success
        c.exec(cmd) do |ch, success|
          channel.on_data do |ch,data|
            stdout_data+=data
            yield if block_given?
          end
        end

        # irrelevant code omitted ...
      end
    end
  end
  [stdout_data, stderr_data, exit_code, exit_signal]
end

block = Proc.new {
  if data.inspect.include? "Proceed?"
    ch.send_data("Y\n")
  end
}

begin
  ssh_config = "/root/git/agil_system_test/test/distributed/ruby/conf/ssh.conf"
  ssh_user = "ec2-user"
  result = []
  Net::SSH.start('some_ssh_alias', ssh_user, :config => ssh_config) do |session|
    result = ssh_exec!(session,command,false, &block)
    # ...
  end
end

Here I just end up getting the error: helper.rb:75:in block in <main>': undefined local variable or methoddata' for main:Object (NameError)

So I'm assuming it's an issue of scope. Is what I'm trying to do possible?

user229044 · Accepted Answer · 2014-03-20 16:12:48Z

2

Yes it's possible, but you need to pass your variables into your block:

channel.on_data do |ch,data|
  stdout_data+=data
  yield(ch, data) if block_given?
end

And your block needs to accept data:

block = Proc.new do |ch, data|
  puts "Yo I'm in the block"
  puts data.inspect
  if data.inspect.include? "Proceed?"
    puts "here"
    ch.send_data("Y\n")
  end
end

The scope of a proc is where it was declared, not where it is invoked.

For example...

def my_method1
  local = "inside"
  block = Proc.new { puts local }
  block.call
end

my_method1 # writes "inside"


def my_method2(&block)
  local = "inside"
  block.call
end

local = "outside"
block = Proc.new { puts local }
my_method2(&block) # writes "outside"

edited Mar 20, 2014 at 16:12

answered Mar 20, 2014 at 16:06

user229044♦

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1 Comment

Madmartigan Over a year ago

Ah magnificent. That was simple. Thanks for the fast response.

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