Invoke

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Invoke is a cloud-based service that leverages blockchain technology to create decentralized marketplaces. The platform connects buyers and sellers through smart contracts, enabling peer-to-peer transactions with no third party involvement or involvement of any kind in the transaction process. It also supports cryptocurrency payments for all goods sold on its marketplace in order to provide an additional layer of security against identity theft during online transactions.

The “invoke vs evoke” is a question that has been asked many times. The difference between the two words is that “invoke” refers to calling up something, while “evoke” means to bring out something.

Invoke

IT pros hardly seldom work on our home computers. We don’t have to use the PowerShell Invoke-Command cmdlet! This cmdlet enables us to write code as if we were working on our local machine.

The Invoke-Command cmdlet is a frequently used PowerShell cmdlet that enables the user to run code inside of a PSSession by leveraging the PowerShell Remoting capability. This PSSession may be one that was previously established using the New-PSSession cmdlet, or it can rapidly create and destroy a temporary session.

The Ultimate Guide to PowerShell Remoting

Consider Invoke-Command to be the PowerShell equivalent of psexec. The premise is the same, regardless of how they are executed. Run a piece of code or a command “locally” on the distant machine.

You must have PowerShell Remoting configured and accessible on the remote machine for Invoke-Command to operate. All Windows Server 2012 R2 or later computers have it enabled by default, along with the necessary firewall exceptions. If you still have Server 2008 machines, there are a several options for setting up Remoting, one of which is to execute winrm quickconfig or Enable-PSRemoting on the remote system.

Let’s imagine you have a distant Windows Server 2012 R2 or later domain-joined PC and you want to illustrate how Invoke-Command works with a “ad-hoc command,” meaning one that doesn’t need the creation of a new PSSession. When working on a workgroup PC, things might become a bit messy. I’ll start by typing Invoke-Command into my PowerShell terminal and pressing Enter.

PS> Invoke-Command cmdlet Invoke-Command at command pipeline position 1 Supply values for the following parameters: ScriptBlock:

I’m requested to supply a scriptblock right now. The scriptblock contains the code that will be executed on the remote machine.

Let’s run the hostname command to verify that the code within the scriptblock is being executed on the distant machine. The hostname of the machine on which this program is executing will be returned. Running hostname on my local computer returns the name of the machine.

Let’s now give a scriptblock to Invoke-Command with the same code inside of it. But, before we do anything, there’s one thing we need to remember: ComputerName. We must inform Invoke-Command which remote machine this command should be executed on.

PS> Invoke-Command -ScriptBlock { hostname } -ComputerName WEBSRV1 WEBSRV1

The name of the remote machine WEBSRV1 is now shown in the output of hostname. You’ve used WEBSRV1 to execute some code. The simplest use of Invoke-Command is to run basic code within a scriptblock and transfer it to a single remote computer, but it can do so much more.

Local Variables are Passed to Remote Scriptblocks

There won’t be a single Invoke-Command reference in your script. Your script will most likely be dozens of lines lengthy, with variables declared in specific locations and functions created in modules, among other things. Even while wrapping some code in a handful of curly brackets may seem to be harmless, you’re really modifying the scope in which the code runs. After all, you’re transmitting that code to a machine on the other side of the world. Except for what’s in the scriptblock, the distant computer has no information about all of the local code on your system.

You may have a function with a machine name and a file path argument, for example. The objective of this function is to launch a software installation on the remote machine. You may provide the installer the name of the machine and the “local” file path if the installer is already installed on the remote computer.

Isn’t the following function reasonable? Let’s put it to the test.

function Install-Stuff { param( [Parameter(Mandatory)] [ValidateNotNullOrEmpty()] [string]$ComputerName, [Parameter(Mandatory)] [ValidateNotNullOrEmpty()] [string]$InstallerFilePath ) Invoke-Command -ComputerName $ComputerName -ScriptBlock { & $InstallerFilePath } } PS> Install-Stuff -ComputerName websrv1 -InstallerFilePath ‘C:install.exe’ The expression after ‘&’ in a pipeline element produced an object that was not valid. It must result in a command name, a script block, or a CommandInfo object. + CategoryInfo : InvalidOperation: (:) [], RuntimeException + FullyQualifiedErrorId : BadExpression + PSComputerName : websrv1

Due to my usage of the ampersand operator, it fails with an obfuscated error message. Even though you gave a value in with the function argument, the code failed because $InstallerFilePath was empty. We may test this by substituting Write-Host for the ampersand.

Invoke-Command -ComputerName $ComputerName -ScriptBlock Write-Host “Installer path is: $InstallerFilePath” is a new function line.

PS> Install-Stuff -ComputerName websrv1 -InstallerFilePath ‘C:install.exe’ Installer path is: PS>

It’s worth noting that the value of $InstallerFilePath is null. Because it wasn’t transmitted to the remote computer, the variable hasn’t been enlarged. We have two alternatives for passing locally created variables to the remote scriptblock: prefix the variable name with $using: within the scriptblock or use the Invoke-Command parameter ArgumentList. Let’s have a look at both of them.

The ArgumentList parameter is used to provide a list of arguments.

The Invoke-Command ArgumentList option is one technique to provide local variables to a remote scriptblock. This argument enables you to send local variables to it and use placeholders instead of local variable references in the scriptblock.

Passing the local variables to The ArgumentList parameter is used to provide a list of arguments. is easy.

Invoke-Command -ComputerName WEBSRV1 -ScriptBlock { & $InstallerFilePath } -ArgumentList $InstallerFilePath

The part that trips up some people is how to structure the variables inside of the scriptblock. Instead of using { & $InstallerPath }, we need to change it to either be { & $args[0] } or {param($foo) & $foo }. Either way works the same but which one should you use?

The ArgumentList parameter is used to provide a list of arguments. is an object collection. Object collections allow you to pass one or more objects at a time. In this instance, I’m just passing one.

When the Invoke-Command cmdlet is used, it takes the collection and injects it into the scriptblock, converting it to an array named $args. It’s important to remember that $args -eq ArgumentList. At this point, you would refer to each index in the collection as if it were an array. In our situation, the collection only contained one element ($InstallerFilePath), which “translated” to $args[0], the collection’s initial index. If you had more, you would refer to them as $args[1], $args[2], and so on.

You may also provide arguments to the scriptblock, exactly like a function, if you’d want to give the scriptblock variables nicer names. After all, a scriptblock is nothing more than a call to an anonymous function. Generate a param block with the parameter’s name to create scriptblock parameters. After that, refer to that argument in the scriptblock as seen below.

Invoke-Command -ComputerName WEBSRV1 -ScriptBlock { param($foo) & $foo } -ArgumentList $InstallerFilePath

In this case, the items in the ArgumentList collection are “mapped” to the declared parameters in the order they appear in the ArgumentList collection. It is the order of the parameters that matters, not their names. Invoke-Command will check for the first argument in the ArgumentList collection and map those values, then do the same for the second, third, and so on.

The $Application Construct

The $Application Construct is another popular way to pass local variables to a remote scriptblock. This construct allows you to reuse the existing local variables but simply prefacing the variable name with $using:. No need to worry about an $args collection nor adding a parameter block.

Invoke-Command -ComputerName WEBSRV1 -ScriptBlock { & $using:InstallerFilePath }

The $using construct in PowerShell is a lot easier, but if you ever go into Pester, you’ll find that ArgumentList is your best buddy.

New-PSSession and Invoke-Command

Although this essay is really on Invoke-Command, we must quickly discuss the New-PSSession command to illustrate its use. Remember how I said before that Invoke-Command may employ “ad-hoc” commands or existing sessions?

We’ve been executing “ad-hoc” commands on distant machines throughout this article. We’ve been starting fresh sessions, executing code, and then shutting them off. This is OK for one-time use, but not when you’re running hundreds of commands on the same machine. In this scenario, it’s preferable to utilize an existing PSSession rather than create one ahead of time using New-PSSession.

You must first establish a PSSession using New-PSSession before performing any instructions. We may accomplish this by typing $session = New-PSSession -ComputerName WEBSRV1 on the command prompt. This establishes a remote session on the server as well as a local reference to that session. At this point, I can replace ComputerName with Session and direct Session to my $session variable that I’ve stored.

Invoke-Command -Session $session -ScriptBlock { & $using:InstallerFilePath }

Because the session has already been constructed, you’ll notice that performance is quicker when it’s run. However, it’s critical to use Remove-PSSession to close the open session after it’s finished.

Summary

The Invoke-Command is a command that is used to invoke anything. The PowerShell cmdlet is one of the most widely used and powerful cmdlets. It’s the one I use the most out of almost all of them. Its simplicity of usage and ability to execute any code on distant systems makes it a command I highly suggest learning from the ground up!

invoke upon” is a command-line tool that allows users to invoke scripts, binaries, and other program files. The “invoke upon” command can be used on Linux, Mac OS X, and Windows systems.

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