Ezine 189 - PowerShell Sort-Object and -GroupBy
Introduction to PowerShell Sort-Object and -GroupBy
It's so much easier to read a list when the columns are sorted into a
meaningful order.
As PowerShell interprets a script, so it often has to deal with raw data which is not
sequenced either numerically or alphabetically.
Consequently, a good programmer will add an instruction
to sort or group the columns on the most important property.
Topics for PowerShell Sort-Object
To this day, I still have trouble finding certain Windows services, for example,
where in the list is the firewall? Why can't I find the print spooler
under the letter 'P'? My memory and experience tell me these
services are there somewhere, but what
does Microsoft call them? The answer is to focus not on 'Name', but
'DisplayName' and then apply sort-Object to this property.
Before we start experimenting with sorting and grouping the output, let me introduce the
cmdlet which will be the vehicle for our study, namely: get-Service.
Incidentally, the nouns in PowerShell's cmdlets are always singular hence
service (and not serviceS).
get-Service | Sort-Object DisplayName
Note 1: If you disregard PowerShell's pipe (|)
then sort-Object won't work.
The idea is that we get a raw list of services and then squirt them into
the sort-Object cmdlet; naturally, we provide the name of the property that
is going to act as the primary key for our sort, in this example we will use
DisplayName.
Note 2: You can abbreviate sort-Object to
plain sort thus: get-service | sort displayName
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Background Research with Get-Member
Never miss an opportunity to run get-Member (gm) against any cmdlet that
you are studying. In the case of get-Service, preceding it with
get-Member reveals interesting properties such as 'DependentServices', 'ServiceDependsOn'
and CanStop. Do remember the pipe symbol thus:
get-Service | get-Member
Armed with information from get-Member about the additional properties of Windows services, we need a method of
selecting the names and position of these extra columns in the output, for
this we append the Format-Table cmdlet. Once again, this example
illustrates how piping the output of the first command, becomes the input of the second
section, and then onwards into the script's third
element. I find it helpful to think of successive pipes as refining
the output.
The key to understanding -GroupBy is to realize that it's a parameter,
which is associated with Format-Table (and other sister cmdlets). There are two
minor traps with -GroupBy, firstly understand how it differs from
Sort-Object. Secondly, appreciate that -GroupBy is a parameter
different from the group-Object cmdlet.
get-Service | Sort-Object Status, DisplayName | `
format-Table
DisplayName, CanStop, Status -groupBy status -auto
Note: There is a lot going on in the above
example. Realize that we can sort on more than one property, firstly Status
and secondly DisplayName. Also observe how this example does not just sort, but also groups the services
into those which are running and those which are stopped.
Make my day: Choose different properties for Format-Table. Also
experiment with
omitting Status from the Sort-Object pipe and appreciate how messy the
output gets when you don't sort on the property that you also want to group.
One more challenge: Which cmdlet supports -auto? Try putting
get-Help before get-Service. Now try help before Format-Table. Any sign of
-AutoSize? My not-so-hidden agenda is to encourage you to
research the full list of parameters available to the cmdlets that you are
using. In this instance you may unearth the -descending parameter,
which is handy for correcting a list that is in the reverse order that you had hoped.
When in default mode, sort-object builds a list in rising order, this is why we
don't need to explicitly add an ascending instruction. For even more
control over the output sequence, type: help sort-Object -full, and then
study example 5.
If you are looking for handy network utilities, try some of the free downloads at
Tools4Ever
For the user, sorting and grouping data make raw data that bit easier to read.
For the programmer, ranking the output gives satisfaction and a sense of a job
well done. In terms of learning PowerShell, the secret is to understand the difference
between the cmdlet sort-Object and the parameter -GroupBy. As usual,
get-Member and get-help... -full have crucial role in researching the full
power of any cmdlet that you employ.
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See more Microsoft PowerShell tutorials
• PowerShell Tutorials •
Methods • Cmdlets
• PS Snapin •
Profile.ps1 • Exchange 2007
•
Command & Expression Mode •
PowerShell pipeline (|) •
PowerShell 'where' •
PowerShell 'Sort'
If you see an error of any kind, do let me know. Please report any factual mistakes, grammatical errors or broken links, I will be happy to not only to correct the fault, but also to give you credit.
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