Start- process vs invoke- command

Start- process vs invoke- command

IT professionals rarely work just on our local computer. This cmdlet allows us to seamlessly write code as if we were working on our local computer. This PSSession can either be one created previously with the New-PSSession cmdlet or it can quickly create and tear down a temporary session as well. Think of Invoke-Command as the PowerShell psexec. Though they are implemented differently, the concept is the same. For Invoke-Command to work though, you must have PowerShell Remoting enabled and available on the remote computer.

By default, all Windows Server R2 or later machines do have it enabled along with the appropriate firewall exceptions. Things get a little messy when working on workgroup computers. This command will return the hostname of the computer it is running on. We have to tell Invoke-Command what remote computer to run this command on.


Running simple code inside of a scriptblock and passing to a single remote machine is the easiest application of Invoke-Command but it can do so much more.

Your script is probably going to be dozens of lines long, have variables defined places, functions defined in modules and so on.

It fails with an obscure error error message due to my use of the ampersand operator. We can test this by replacing the ampersand with Write-Host. One way to pass local variables to a remote scriptblock is to use the Invoke-Command ArgumentList parameter. This parameter allows you to pass local variables to the parameter and replace local variable references in the scriptblock with placeholders.

The part that trips up some people is how to structure the variables inside of the scriptblock. Either way works the same but which one should you use? The ArgumentList parameter is an object collection.

Object collections allow you to pass one or more objects at a time. After all, a scriptblock is just an anonymous function.The Invoke-Expression PowerShell cmdlet can be easy to misunderstand when and when not to use it. That means you should bookmark this page right now!

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Want more tips like this? Without Invoke-Expressiona string submitted at the command line would be returned echoed unchanged. In other words, it can be useful for calling code within a script or building commands to be executed later.

It can also be used cautiously in combination with user provided input. The most basic example of using Invoke-Expression is defining a script and passing that string to the Command parameter. Invoke-Expression then executes that string. However, if you enclose the path item in single or double quotes with the entire string in quotes, Invoke-Expression will execute the script as expected.

The only parameter Invoke-Expression has is Command. There is no native way to pass parameters with Invoke-Expression. However, instead, you can include them in the string you pass to the Command parameter. Perhaps I have a script with two parameters called Path and Force.

Instead of using a specific parameter via Invoke-Expressionyou can pass parameters to that script by passing them as you typically would via the console. You have to include that entire line in a string and then pass that string to the Command parameter. Not really.

start- process vs invoke- command

This means you need to use error handling within your Command parameter. However, the call operator does not parse the command. It cannot interpret command parameters as Invoke-Expression can. Concatenating Get-Process and the parameter will not work as expected using the call operator. The Start-Process cmdlet provides a return or exit code in the returned object.

It allows you to wait for the called process to complete and allows you to launch a process under a different Windows credential.

Invoke-Expression is quick and dirty whereas Start-Process can be more useful for interpreting results of the executed process. Invoke-Commandon the other hand, leverages PowerShell Remoting giving you the ability to invoke code locally or remotely on computers.

Invoke-Command is preferable if you are writing the executed commands now, as you retain intellisense in your IDE whereas Invoke-Expression would be preferable if you wanted to call another script from within your current one.

Understanding PowerShell Scriptblocks

The Invoke-Item cmdlet gives you inline support for multiple paths to open documents with their default action, with parameters for including, excluding, adding credentials, and even confirmation for additional security. If someone had malicious intent they might be able to trick some virus programs by masking malicious code that constructs itself during runtime.

If you have multiple commands to execute, even though Invoke-Expression only accepts a string rather than an array, we can use the PowerShell pipeline to send objects down the pipeline one at a time. You should be very cautious with using Invoke-Expression with user input. If you allow a prompt to a user in a way that gives them access outside of the command you are intending to execute, it could create an unwanted vulnerability.

Here is one way you can safely implement user input with Invoke-Expression. Every cmdlet has their place and Invoke-Expression is one that just about everyone will run into at one point or another.

Adam the Automator. Twitter Facebook LinkedIn. Table of Contents.Many times you can execute a command by just typing its name, but this will only run if the command is in the environment path. Also if the command or the path contains a space then this will fail. If you need to run a specific type of command which may not be the highest priority use Get-Command.

For example if you have an external command called Ping and a function also called ping, normally the function will be run as it has higher priority, Get-Command -commandType Application Ping will return the external application instead. If you need to capture a return value from the new process, store the output the process generates stdout and stderr and control the style or visibility of the Window, then use Start-Process which makes all those options available.

EchoArgs is a simple utility that spits out the arguments it receives. This is very useful for testing, just replace the program name in your script with EchoArgs. Invoking a command either directly or with the call operator will create a child scope that will be thrown away when the command exits. To avoid this and preserve any changes made to global variables you can ' dot ' the script which will execute the script in the current scope.

Dot sourcing runs a function or script within the current scope. Run the script mycommand. Requires -Version 3. Run a PowerShell script - More examples of running scripts.

Invoke-Command - Run commands on local and remote computers. Invoke-Expression - Run a PowerShell expression. Start-Process - Start one or more processes, optionally as a specific user. Keith Hill's blog - Command parsing mode vs Expression parsing mode.

SS64 PowerShell How-to.Invoke-Command runs commands on a local or remote computer and returns all output from the commands, including errors. A single Invoke-Command command, can run commands on multiple computers. To run a single command on a remote computer, use -ComputerName. To run a series of related commands that share data, create a PSSession a persistent connection on the remote computer, and then use Invoke-Command -Session to run the command in the PSSession.

When retrieving information from a remote machine PowerShell will by default return an object with a large number of properties, performance can be greatly improved by using Select-Object to return only the properties needed. Invoke-Command may also be used on a local computer to evaluate or run a string in a script block as a command. PowerShell converts the script block to a command and runs the command immediately in the current scope, instead of just echoing the string at the command line.

start- process vs invoke- command

Run the Test. The script is located on the local computer.

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The script runs on the remote computer and the results are returned to the local computer:. Run a script block containing just a Get-Culture command on the Server64 computer. Pass user credentials with permission to run the command:. Save a command in a local variable, then use Invoke-Command to run the command against several remote computers:.

Run a background job on two remote computers. Because the Invoke-Command command uses the AsJob parameter, the commands run on the remote computers, but the job actually resides on the local computer and the results are transmitted to the local computer:.

Run the Sample. Using the -FilePath parameter to specify the script file has the effect that the content of the script is automatically copied into a script block and then passed to and run on each of the remote computers:. Get-Command - Retrieve basic information about a command. Invoke-Expression - Run a PowerShell expression. Invoke-History - Invoke a previously executed Cmdlet. Start-Process - Start one or more processes, optionally as a specific user. SS64 PowerShell How-to.This is similar to using Invoke-Expression for string commands.

The secret of success with Invoke-Command is to pay particular attention to these three parameters:. Get-Help When investigating the scope and parameters for any new command, I call for Get-Help followed by the name of the cmdlet, this is how I learned about the above parameters. Before you run the script block on a remote computer, I always like to get it working on the local machine:.

Remote Computer Now we are ready to progress to a remote computer. Please substitute a computer on your network for Victim1. Note 2: If the ScriptBlock does not do what you want, and you wish to append string commands, try Invoke-Expression instead.

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Using the -FilePath parameter is an alternative technique to employing -ScriptBlock. The idea is that you store all the PowerShell instructions in a.

Note 6: Talking of files, you could also store a list the servers, which you want to run the instructions, in a file and then call that file. Jobs and -asJob For scripts that take a long time to complete you could consider appending the — asJob parameter. This has the pleasant effect of running the commands in the background. However, to actually see the results, you need to master the cmdlet receive-Job.

As an alternative to -asJob you could be to employ the -session parameter then run Start-job. However, from a learning perspective, I normally like to concentrate on one technique at a time and combining Invoke-Command with start-Job is a tricky task for a beginner.

Thankfully the utilities are displayed logically: monitoring, network discovery, diagnostic, and Cisco tools. A typical scenario is where you can typing command-line instructions, but now you want to execute the same string using PowerShell. With Invoke-Expression you can either save the string values in a text file, then execute them, else append the string directly to Invoke-Expression.Things can get tricky when an external command has a lot of parameters or there are spaces in the arguments or paths!

With spaces you have to nest Quotation marks and the result it is not always clear! In this case it is better to separate everything like so:. There are multiple ways to use the Create method. Office Office Exchange Server.

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PowerShell: Running Executables. How do you know which one to use for the job? Here is an outline of the methods with examples and general use. Table of Contents. Runs a ping, no. A test app that is run from the local folder but must be prefixed with the. Runs Get-Process. This will return the directory listing as a string but returns much faster than a GCI. ExitCode to find available Verbs use the following code. ProcessStartInfo -args PowerShell.

Process]::Start "notepad. ReadToEnd. Opens a notepad process using [wmiclass] accelerator. Opens a notepad process with process startup configuration to hide the window using [wmiclass] accelerator. Properties[ 'ShowWindow' ].

Opens a batch file process using [wmiclass] accelerator on remote system. Typical Return object showing processid and returnvalue. ProcessId : ReturnValue : 0. In V3 you can use the stop-parsing symbol.The Start-Process cmdlet starts one or more processes on the local computer.

By default, Start-Process creates a new process that inherits all the environment variables that are defined in the current process. To specify the program that runs in the process, enter an executable file or script file, or a file that can be opened by using a program on the computer.

If you specify a non-executable file, Start-Process starts the program that is associated with the file, similar to the Invoke-Item cmdlet. You can use the parameters of Start-Process to specify options, such as loading a user profile, starting the process in a new window, or using alternate credentials. This example starts a process that uses the Sort.

The command uses all of the default values, including the default window style, working folder, and credentials. This example starts a process that sorts items in the Testsort. Any errors are written to the SortError. The UseNewEnvironment parameter specifies that the process runs with its own environment variables. This example starts the Notepad. It maximizes the window and retains the window until the process completes. This example shows how to find the verbs that can be used when starting a process.

The available verbs are determined by the filename extension of the file that runs in the process. The example uses New-Object to create a System. ProcessStartInfo object for PowerShell.

Both commands start the Windows command interpreter, issuing a dir command on the Program Files folder. Because this foldername contains a space, the value needs surrounded with escaped quotes. Note that the first command specifies a string as ArgumentList. The second command is a string array.

On Windows, Start-Process creates an independent process that remains running independently of the launching shell. On non-Windows platforms, the newly started process is attached to the shell that launched. If the launching shell is closed, the child process is terminated. To avoid terminating the child process on Unix-like platforms, you can combine Start-Process with nohup.

The following example launches a background instance of PowerShell on Linux that stays alive even after you close the launching session. The nohup command collects output in file nohup. In this example, Start-Process is running the Linux nohup command, which launches pwsh as a detached process.

start- process vs invoke- command

For more information, see the man page for nohup. Specifies parameters or parameter values to use when this cmdlet starts the process. Arguments can be accepted as a single string with the arguments separated by spaces, or as an array of strings separated by commas. If parameters or parameter values contain a space, they need to be surrounded with escaped double quotes. Specifies a user account that has permission to perform this action. By default, the cmdlet uses the credentials of the current user.

If you type a user name, you're prompted to enter the password. Specifies the optional path and filename of the program that runs in the process.

Enter the name of an executable file or of a document, such as a. This parameter is required.


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