Can I get continuous output from system calls in Ruby?

Question

When you use a system call in a Ruby script, you can get the output of that command like this:

output = `ls`
puts output

That's what this question was about.

But is there a way to show the continuous output of a system call? For example, if you run this secure copy command, to get a file from a server over SSH:

scp user@someserver:remoteFile /some/local/folder/

... it shows continuous output with the progress of the download. But this:

output = `scp user@someserver:remoteFile /some/local/folder/`
puts output

... doesn't capture that output.

How can I show the ongoing progress of the download from inside my Ruby script?

Answer 1

Try:

IO.popen("scp -v user@server:remoteFile /local/folder/").each do |fd|
  puts(fd.readline)
end

Answer 2

I think you would have better luck using the ruby standard library to handle SCP (as opposed to forking a shell process). The Net::SCP library (as well as the entire Net::* libraries) are full featured and used with Capistrano to handle remote commands.

Checkout http://net-ssh.rubyforge.org/ for a rundown of what is available.