This technique for understanding PowerShell's Workflow is very much
my own making. It is designed to illustrate the three keywords
'Workflow, Parallel and Sequence'.
The only point of this basic example is to demonstrate how Workflow operates
with a cmdlet or 'wrapper'. Once I
grasped this cmdlet / wrapper idea it was relatively straightforward to add
'Sequence' and 'Parallel' sections to my workflow.
# Most Basic PowerShell Workflow Example Workflow Verb-Noun { "Stuff!" }
Clear-Host Verb-Noun
Important: Nothing happens if you omit the last
line: Verb-Noun
The underlying PowerShell task here is to execute Get-Process and then
Get-Service, but padded with a few literal lines of "In x of y".
In truth, this is an example to learn about workflow rather than performing
any useful tasks.
From a Workflow perspective, take the time to trace the three parallel
items, and the two sequence items both in the script and in the results.
Principle: Get this example working, then experiment by
re-ordering the elements.
# PowerShell 3.0 Workflow Example Workflow Guy-ParaSeq { # Commands within Parallel execute in any
order Parallel { "In parallel 1 of 3" Sequence { "In sequence 1 of 2"
Get-Process -Name Power* "In
sequence 2 of 2"
} # Closes Sequence "In parallel 2 of 3" Get-Service -Name W32Time "In parallel 3
of 3" } # Closes Parallel } # Closes
Guy-ParaSeq cmdlet
Clear-Host Guy-ParaSeq
Note 1: Observe how 'In sequence 2 of 2' has to wait
for Get-Process to finish, however, 'In parallel 2 of 3' does not have to wait.
Note 2: It's crucial to run Guy-ParaSeq on the last line.
# Windows PowerShell Workflow Example Workflow Guy-ParaSeq1 { Parallel { "In parallel 1 of 3" Get-Process -Name Power*
Sequence { "In sequence 1 of 2" "In
sequence 2 of 2"
} "In parallel 2 of 3" Get-Service -Name W32Time "In parallel 3
of 3" } # Closes Parallel } # Closes
cmdlet
Clear-Host Guy-ParaSeq1
Note 3: I hope that these two examples will encourage you
to experiment with the order of Parallel and Sequence items.
Free Monitor for Your Network: SolarWinds Real-time Traffic Analyzer
The main reason for monitoring your network is to check at a glance which
servers are available. If there is a network problem you
want an interface to show the scope of the problem immediately.
Even when all servers and routers are available, sooner or later you will be curious to
know who, or what, is hogging the precious network's bandwidth. A GUI
showing the top 10 users always makes interesting reading.
Another reason to monitor network traffic is to learn more about your
server's response times and the consumption of resources. To take the pain out of
capturing frames and analysing the raw data, Guy recommends that you download a copy of
the SolarWinds
free Real-time NetFlow Analyzer.
A number of ordinary PowerShell commands give errors in workflow, the way
around these difficulties is to employ InlineScript.
Workflow Guy-ParaSeqInline { Parallel { Get-Process -Name Svchost*
Sequence { "In sequence 1 of 2" InlineScript { Start-Sleep 10
} "In sequence 2 of 2"
} # Closes Sequence "In parallel 1 of 2" "In parallel 2 of 2" InlineScript {
$a = 9 $b = $a+2 $b
} Get-Service -Name W32Time } # Closes
Parallel }
Clear-Host Guy-ParaSeqInline
Note 4: Observe how this script employs Start-Sleep to
emphasise the parallel and sequence portions, if you don't see what
I mean then experiment by moving the commands around and pay
attention to 'In parallel x of y'.
Good project management takes a task and breaks it down into steps, each
with resources and a time-line. Workflow charts display which tasks
can be tackled simultaneously, for instance fuelling cars at a big gas
(petrol) station, and which are constrained by the need for activities to
complete in sequence, for example, an insurance claim form.
Workflow in PowerShell In script performance terms we can make gains by identifying which jobs
can be executed in parallel. This pre-supposes that we are comfortable
with PowerShell's jobs, a factor which rules out PowerShell novices.
The first point to remember is that this cmdlet is only available on
PowerShell v 3.0 and later. I found Update-Help particularly difficult
to configure so that it delivered the package of revised help files.
If you like this page then please share it with your friends
