Can Powershell Run Commands in Parallel?

You can execute parallel jobs in Powershell 2 using Background Jobs. Check out Start-Job and the other job cmdlets.

# Loop through the server listGet-Content "ServerList.txt" | %{  # Define what each job does  $ScriptBlock = {    param($pipelinePassIn)     Test-Path "\\$pipelinePassIn\c`$\Something"    Start-Sleep 60  }  # Execute the jobs in parallel  Start-Job $ScriptBlock -ArgumentList $_}Get-Job# Wait for it all to completeWhile (Get-Job -State "Running"){  Start-Sleep 10}# Getting the information back from the jobsGet-Job | Receive-Job

The answer from Steve Townsend is correct in theory but not in practice as @likwid pointed out. My revised code takes into account the job-context barrier--nothing crosses that barrier by default! The automatic $_ variable can thus be used in the loop but cannot be used directly within the script block because it is inside a separate context created by the job.

To pass variables from the parent context to the child context, use the -ArgumentList parameter on Start-Job to send it and use param inside the script block to receive it.

cls# Send in two root directory names, one that exists and one that does not.# Should then get a "True" and a "False" result out the end."temp", "foo" | %{  $ScriptBlock = {    # accept the loop variable across the job-context barrier    param($name)     # Show the loop variable has made it through!    Write-Host "[processing '$name' inside the job]"    # Execute a command    Test-Path "\$name"    # Just wait for a bit...    Start-Sleep 5  }  # Show the loop variable here is correct  Write-Host "processing $_..."  # pass the loop variable across the job-context barrier  Start-Job $ScriptBlock -ArgumentList $_}# Wait for all to completeWhile (Get-Job -State "Running") { Start-Sleep 2 }# Display output from all jobsGet-Job | Receive-Job# CleanupRemove-Job *

(I generally like to provide a reference to the PowerShell documentation as supporting evidence but, alas, my search has been fruitless. If you happen to know where context separation is documented, post a comment here to let me know!)

There's so many answers to this these days:

1. jobs (or threadjobs in PS 6/7 or the module for PS 5)
2. start-process
3. workflows (PS 5 only)
4. powershell api with another runspace
5. invoke-command with multiple computers, which can all be localhost (have to be admin)
6. multiple session (runspace) tabs in the ISE, or remote powershell ISE tabs
7. Powershell 7 has a foreach-object -parallel as an alternative for #4

Using start-threadjob in powershell 5.1. I wish this worked like I expect, but it doesn't:

echo yahoo.com facebook.com |   start-threadjob { test-netconnection $input } | receive-job -wait -autoWARNING: Name resolution of yahoo.com microsoft.com facebook.com failed

It works this way. Not quite as nice and foreach-object -parallel in powershell 7 but it'll do.

echo yahoo.com facebook.com |   % { $_ | start-threadjob { test-netconnection $input } } |   receive-job -wait -auto | ft -aComputerName RemotePort RemoteAddress PingSucceeded PingReplyDetails (RTT) TcpTestS                                                                           ucceeded------------ ---------- ------------- ------------- ---------------------- --------facebook.com 0          31.13.71.36   True          17 ms                  Falseyahoo.com    0          98.137.11.163 True          97 ms                  False

Here's workflows with literally a foreach -parallel:

workflow work {  foreach -parallel ($i in 1..3) {     sleep 5     "$i done"   }}work3 done1 done2 done

Or a workflow with a parallel block:

function sleepfor($time) { sleep $time; "sleepfor $time done"}workflow work {  parallel {    sleepfor 3    sleepfor 2    sleepfor 1  }  'hi'}    work sleepfor 1 donesleepfor 2 donesleepfor 3 donehi

Here's an api with runspaces example:

$a =  [PowerShell]::Create().AddScript{sleep 5;'a done'}$b =  [PowerShell]::Create().AddScript{sleep 5;'b done'}$c =  [PowerShell]::Create().AddScript{sleep 5;'c done'}$r1,$r2,$r3 = ($a,$b,$c).begininvoke() # run in background$a.EndInvoke($r1); $b.EndInvoke($r2); $c.EndInvoke($r3) # wait($a,$b,$c).streams.error # check for errors($a,$b,$c).dispose() # cleana doneb donec done