Get PowerShell output in Ruby

Question

I am writing some automation script that needs to run PowerShell commands on a remote machine using Ruby. In Ruby I have the following code:

def run_powershell(powershell_command)
    puts %Q-Executing powershell #{powershell_command}-
    output =  system("powershell.exe  #{powershell_command}")
    puts "Executed powershell output #{output}"
end

I can pass in Invoke-Command based ps1 files and everything works as expected. I can see the output in the console when I run the command.

The only problem is that there is no way to find out if the command run was successful; sometimes PowerShell is clearly throwing errors (like not able to get to the machine), but the output is always true.

Is there a way to know if the command ran successfully?

Check for `$?` automatic variable after powershell execution. http://technet.microsoft.com/en-us/library/hh847768.aspx — Aleksei Matiushkin, Oct 01 '14 at 07:00

score 6 · Answer 1 · edited May 23 '17 at 10:29

system(...) will actually return a value saying if it succeeded, not the output of the call.

So you can simply say

success = system("powershell.exe  #{powershell_command}")
if success then
    ...
end

If you want both the output and return code, you can use `backticks` and query $? for the exit status (not the same $? as linked to in the comment to the question, by the way.)

output = `powershell.exe  #{powershell_command}`
success = $?.exitstatus == 0

If you want a more reliable way that will escape things better, I'd use IO::popen

output = IO::popen(["powershell.exe", powershell_command]) {|io| io.read}
success = $?.exitstatus == 0

If the problem is that powershell itself isn't exiting with an error, you should have a look at this question

So, correct me if I'm getting this wrong but: `IO::popen(["powershell.exe", 'Write-Host "doing stuff"']) {|io| io.read}` should return `"doing stuff"`? Because when I run this, the powershell definitely runs, but nothing is returned by `IO::popen`... — Sancarn, Nov 21 '17 at 14:45

DivineOps · Answer 2 · 2015-08-10T22:57:51.013

There is another option, and that is running the PowerShell from cmd. Here is the (pretty hard to figure out) syntax:

def powershell_output_true?()
  ps_command = "(1+1) -eq 2"
  cmd_str = "powershell -Command \" " + ps_command + " \" "
  cmd = shell_out(cmd_str, { :returns => [0] })
  if(cmd.stdout =~ /true/i)
     Chef::Log.debug "PowerShell output is true"
    return true
  else
    Chef::Log.debug "PowerShell output is false"
    return false
  end
end

I am comparing the stdout to true, but you can compare it to whatever you need. described in blog

Get PowerShell output in Ruby

2 Answers2