Powershell: Adding background job support to script cmdlets

Recently I’ve been writing a lot of script cmdlets in modules. One such cmdlet is used to wrap an executable which has the tendency to take a very long time to complete and I needed to run it more than ten times back to back. To attempt to speed things up I thought it would be great to add an –AsJob parameter to my script cmdlet. This way the cmdlet returns me a Powershell background job so that I can spin up multiple instances of my script cmdlet at the same time. Below is an example of my approach to implementing the –AsJob parameter to a simple script cmdlet.

Enjoy!

 1 function Test-Job {
 2     [CmdletBinding()]
 3     param (
 4         [parameter(mandatory=$true)] [String] 
 5             $Computer,
 6             
 7         [parameter()] [Int16] 
 8             $Retries = 4,
 9         
10         [parameter()] [Switch]
11             $AsJob
12     )
13     
14     $ScriptBlock = {
15         [CmdletBinding()]
16         param (
17             [parameter(mandatory=$true)] [String] 
18                 $Computer,
19                 
20             [parameter()] [Int16] 
21                 $Retries = 4
22         )
23         
24         $output = & ping.exe $Computer -n $Retries 2>&1
25         
26         if ($LASTEXITCODE -ne 0) {
27             throw $output
28         } else {
29             $output
30         }
31     }
32     
33     if ($AsJob) {
34         Start-Job -ScriptBlock $ScriptBlock -ArgumentList `
35                 $Computer, $Retries
36     } else {
37         Invoke-Command -ScriptBlock $ScriptBlock -ArgumentList `
38                 $Computer, $Retries
39     }
40 }
41 
42 # Fails.
43 $job = Test-Job -Computer 127.0.0.0 -Retries 6 -AsJob
44 Wait-Job -Job $job 
45 Receive-Job $job
46 
47 # Succeeds.
48 $job2 = Test-Job -Computer 127.0.0.1 -Retries 6 -AsJob
49 Wait-Job -Job $job2
50 Receive-Job $job2
51 
52 # Fails.
53 Test-Job -Computer 127.0.0.0 -Retries 6
54 
55 # Succeeds.
56 Test-Job -Computer 127.0.0.1 -Retries 6