About Sequence



Describes the Sequence keyword, which runs selected activities sequentially.


The Sequence keyword runs selected workflow activities sequentially, that is, they run in the order in which they appear and do not run concurrently. The Sequence keyword is valid only in a Windows PowerShell Workflow.

The Sequence keyword is typically used in a Parallel script block to run selected commands sequentially.

Because workflow activities run sequentially by default, the Sequence keyword effective only in a Parallel script block. However, it valid outside of a Parallel script block, even if it has no effect.

The Sequence script block lets you run more commands in parallel by allowing you to run dependent commands sequentially.


workflow { Sequence { [] []


} }

workflow { Parallel { [] Sequence { [] []


} } }


The commands in a Parallel script block can run concurrently. The order in which they run is not determined. This feature improves the performance of a script workflow.

You can use a Sequence script block to run selected activities sequentially, even though the activities appear in a Parallel script block.

The activities in a Sequence script block run one at a time in the order in which they are listed. An activity in a Sequence script block starts only after the previous activity completes.

However, when the Sequence script block appears in a Parallel script block, the order in which the Sequence script block runs is not determined. It might run before, after, or concurrent with other activities in the Parallel script block.

For example, the following workflow includes a Parallel script block that runs activities that get processes and services on the computer. The Parallel script block contains a Sequence script block that gets information from a file and uses the information as input to a script.

The Get-Process, Get-Service and hotfix-related commands are independent of each other and can run concurrently or in any order, but the command that gets the hotfix information must run before the command that uses it.

workflow Test-Workflow { Parallel { Get-Process Get-Service

Sequence { $Hotfix = Get-Content D:\HotFixes\Required.txt Foreach ($h in $Hotfix} {D:\Scripts\Verify-Hotfix -Hotfix $h} } } }


"Writing a Script Workflow" (http://go.microsoft.com/fwlink/?LinkID=262872) about_ForEach about_ForEach-Parallel about_Language_Keywords about_Parallel about_Workflows