PowerShell Script Files: Get-Content Cmdlet
The ability to 'Get-Content' is useful for itself; moreover, this cmdlet illustrates how easily PowerShell deals with reading from text files. Incidentally, this page also demonstrates looping, which is 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.
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
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 content of each cycle is controlled by $_, the resulting output is merely a list of names.
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
Note 3: 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 4: To gain perspective, and ideas, you could try:
Note 5: The tiny vertical | tells PowerShell to output the contents of $WMI into the second part of that line.
Windows Management Instrumentation (WMI) is one of the hidden treasures of Microsoft's 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. Give this WMI monitor a try - it's free.
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.
If you remember, our mission was to create a PowerShell script, which ran WMI commands against a list of network machines.
# PowerShell script to check running services on a list of computers
Note 6: 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 7: Ft means Format-Table. I have chosen just three properties, name of the service, its state (running) and status.
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.
# PowerShell Content Cmdlet Research
Get-Content Alias 'Type'
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
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 Cmdlet
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.
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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.