Chefの`shell_out`と`shell_out!`、違いと使い分け ref: http://qiita.com/sawanoboly/items/43bc9e15739355f9c533

file4.txt

> result = shell_out!('ps | grep hogehgoe', :returns => 1)
=> <Mixlib::ShellOut#18867260:
  command: 'ps | grep hogehgoe'
  process_status: #<Process::Status: pid 16586 exit 1>
  stdout: ''
  stderr: ''
  child_pid: 16586
  environment: {"LC_ALL"=>"C"}
  timeout: 600
  user: 
  group: 
  working_dir: 
>

## ArrayでもOK
> result = shell_out!('ps | grep hogehgoe', :returns => [1,3,5,7,9])

file5.txt

> shell_out('hogehgoe')
Errno::ENOENT: No such file or directory - hogehgoe
from /opt/chef/embedded/lib/ruby/gems/1.9.1/gems/mixlib-shellout-1.2.0/lib/mixlib/shellout/unix.rb:268:in `exec'

Pry_Console

> result = shell_out!('ps | grep hogehgoe')
Mixlib::ShellOut::ShellCommandFailed: Expected process to exit with [0], but received '1'
---- Begin output of ps | grep hogehgoe ----
STDOUT: 
STDERR: 
---- End output of ps | grep hogehgoe ----
Ran ps | grep hogehgoe returned 1
from /opt/chef/embedded/lib/ruby/gems/1.9.1/gems/mixlib-shellout-1.2.0/lib/mixlib/shellout.rb:251:in `invalid!'