Background Job

A background job is a job running on another PowerShell process(sub-shell) created by the current PowerShell instance.

• Start-Job: start a background job(process job)

  • -ScriptBlock: specify custom action for the job
  • -FilePath: run from a script file
  • -Name: specify name for the job
  • -InitializationScript: preparation for the action run in current PowerShell process
  • -WorkingDirectory: specify cwd for the job
  • -ArgumentList: arguments to be passed into the process
  • -PSVersion: run in specific version

• &: syntactic shorthand for Start-Job

• Receive-Job: retrieve job state from a job object.

  • -Wait synchronously wait for the job.

Start a Job

Start-Job creates a new background job and returns a System.Management.Automation.PSRemotingJob to represent the state of the job.

Start-Job -ScriptBlock { foo }

Using & PowerShell 6+

Using & to create a background job is only equivalent to Start-Job -ScriptBlock { ... }

$job = gps pwsh &
# equivalent to 
$job = sajb { gps pwsh }

& can be recognized as a statement terminator, so you don't have to use an extra ; for multiple expression inline.

gps pwsh &; rcjb $job -Wait
gps pwsh & rcjb $job -Wait # ; can be elided

Passing Arguments

Closure is not allowed for -ScriptBlock.

$foo = 'pwsh'
$job = sajb { gps $foo }
rcjb $job # receive error message

$job = sajb { gps $args } -ArgumentList pwsh,notepad # [!code highlight] 
rcjb $job # ok

Run as Job from other Cmdlet

There's some other cmdlet supports -AsJob switch to perform action as backgraound jobs, like ForEach-Object and Invoke-Command.

# Run a job in the remote
Invoke-Command -HostName <host> -UserName <usr> -ScriptBlock { foo } -AsJob

Querying Jobs