The ability to 'Get-Content' is useful for itself; moreover, this cmdlet
illustrates how easily PowerShell
deals with reading from text files. This page also demonstrates
looping, a classic job for automation via scripting, and a task that PowerShell
delivers with deceptive ease.
Our mission is to employ PowerShell and WMI for checking the status of
the operating system's services. The role of Get-Content is merely to read a list of hostnames,
as a result we can run the WMI code against remote machines.
For ease of learning, and so that you could re-cycle the building blocks, I
have broken down the mission into three self-contained tasks.
In order to
understand my goal let us isolate the PowerShell commands that query the
local computer to see which services are running. Once that works we
want to extend the scope of the script so that it queries other machines on your
network.
Reading lines from a text file is a classic job for a loop. In
PowerShell we can initiate the loop with a 'Foreach' statement. Inside
that loop we use Get-Content to read the names of the computers held in a
named
text file.
Pre-requisites
Create a text file, make a note of the path as well as the filename.
Another trivial point, you need to type a list of hostnames
corresponding to the computers you wish to interrogate.
Disable the firewall on both the source computer, where the script executes, and
also on the destination machine(s) which we wish to interrogate.
I don't want to stray too far from the main objective which is to master Get-Content,
but as a separate mini-project you could obtain a list of computers which
are active
on your network by using WMI's Win32_PingStatus. However, for now we
will assume that you have a list of computers safely stored in a file called NetMachines.txt.
The only purpose of this script is to list the contents of a file line-by-line.
# PowerShell script to list each line of a file $File =
"E:\PowerShell\Loops\NetworkMachines.txt" Get-Content $File | foreach-Object
{ $_ }
Note 1: All we want to achieve in this example is to
practise our Get-Content
technique. Observe how the variable $File controls the source of the text.
Note 2: Foreach-Object provides the loop. The
contents of each cycle are controlled by $_, the resulting output is merely a list of
names.
Guy
Recommends: WMI Monitor and It's Free!
Windows Management Instrumentation (WMI) is one of the hidden
treasures of Microsoft operating systems. Fortunately, Solarwinds
have created a
Free WMI Monitor so that you can discover these gems of performance
information, and thus improve your PowerShell scripts. Take the guess work out of which WMI counters to use when scripting the
operating system, Active Directory or Exchange Server.
In real life this is the portion of the script that you would amend in
order to
tackle a specific problem.
# WMI script to list services which are running on local machine
$Wmi=Get-wmiobject win32_service -filter "state='Running'" $Wmi |
Ft
name, state, status -auto
Note 1: This is just a simple WMI script whose class
is win32_service, just for fun we have filtered only those services that
are running.
Note 2: To gain perspective, and ideas, you could try:
Get-wmiobject win32_service -filter "name='spooler' "
Note 3: The tiny vertical | tells PowerShell to output
the contents of $WMI into the second part of that line.
Running scripts on remote machines has never been easy. Firewalls
and administrative credentials mean that access to another machine is unlikely to be
straight forward. While PowerShell version 2.0 has much better
'Remoting' abilities, here we are dodging some of PowerShell 1.0's
limitations by using WMI's -computername parameter.
Even with everything in our favour, please humour me and make a crucial
configuration change to your machines. Just to get started, I advise that
you suspend normal 'best practice' and disable the firewalls on both the
source (server) and the remote (client) machines. If the script works
then you could investigate other options such as selectively opening ports,
and using -credential. (Incidentally, adding Impersonate and Credential to scripts
rarely works for me.) See how to
disable
Windows 8 firewalls with a Group Policy.
Note 1: This single script combines the tasks of the two
previous scripts. Observe how 'foreach' loops through the list of computer names
controlled by the $File variable. The WMI class win32_service
retrieves services that are running.
Note 2: Ft means format-Table. I have chosen just
three properties, name of the service, its state (running) and status.
Guy Recommends: A Free Trial of the Network Performance Monitor
(NPM)
Solarwinds'
Orion performance monitor
will help you discover what's happening on your network. This
utility will also guide you through troubleshooting; the dashboard will
indicate whether the root cause is a broken link, faulty equipment or
resource overload.
Perhaps the NPM's best feature is the way it suggests solutions to network
problems. Its
second best feature is the ability to monitor the health of individual VMWare
virtual machines. If you are interested in troubleshooting, and creating network maps, then I recommend that you take advantage of Solarwinds' offer.
With Microsoft, there are always at least three ways of doing everything,
what seems like redundancy when you are an expert, seems like perspective
when you are a beginner. Get-Content has not one, but three aliases
check thus:
# PowerShell Alias Type Get-Alias
-definition Get-Content
PowerShell -v- VBScript
In VBScript dealing with files was never straightforward. However,
with PowerShell it's so effortless that you may not realize that the
Get-Content cmdlet opens and closes as part of its
job description.
Incidentally, in PowerShell the mirror image of Get-Content would be
out-File, that is where you append a command to save the output of a script
into a named file. To use Get-Content or out-File all you need is the path
there is no need for any file open or file close
commands because PowerShell takes care of them automatically.
Get-Content is a simple enough cmdlet to understand. What it does is
fetch data information stored in files, for example a list of names from a text file.
Just playing with Get-Content
leads to questions such as 'Why bother', or 'What's the point?' I hope that
your
answer to such questions will give you a PowerShell technique that you can
incorporate in bigger more complex scripts.
»
Summary of PowerShell's Get-Content
If you are coming from scripting languages such as VBScript, you may not be
aware of how easy it is to read from text files in PowerShell.
Get-Content not only reads the data line-by-line, but also deals with
opening and closing the named file automatically.
There is
also Out-File, a very useful
command to save results to disk, rather than write to screen.
If you like this page then please share it with your friends
Please email me if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.
Windows Management Instrumentation (WMI) is one of the hidden
treasures of Microsoft operating systems.
Fortunately, Solarwinds
have created the
Free WMI Monitor so that you can actually see and understand these gems of
performance information. Take the guess work out of which
WMI counters to use for applications like Microsoft Active Directory,
SQL or Exchange Server.
